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PostPosted: Sun Jun 17, 2012 8:20 pm 
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MCS Mixture Control Solenoid Availability VS Usability.

Anyone that owns and maintains an 85-88 MK1 Sprint knows, the carburetors on these cars, mainly the Hitachi DFB306 feedback unit, are not the most popular where carburetors are concerned and near impossible to find parts for. However, if properly maintained and rebuilt, they offer great performance and some of the best economy any car has ever offered even to this day.

One of the key elements that makes its impressive performance possible is the Mixture Control Solenoid, aka MCS. This tiny electro mechanical device works wonders where those impressive mpg numbers come in to play. However, in recent years trying to obtain a new one that works and fits seems to be getting near impossible. I’ve heard all sorts of stories about how many among the 3 cyl crowd have purchased what they are lead to believe is an exact replacement, only to find out that it doesn’t work. Many to abandon reviving the car due to the fact they can’t find the proper part. Of course many never go down the path anyway due to the fact they can’t stomach to spend the cost of the part, on a car they only paid pennies more for. Sadly, it is no doubt why so many of these impressive little cars ended up in junk yards. Me personally, I’ve never heard exactly what it was that didn’t work until I myself recently went on that quest of obtaining a new one. What I am about to share is my research, purchase, and eventual modification to make a readily obtainable one work.

If one does an internet search to no end, one will commonly find what the carburetor parts industry refers to as the MX40. According to all sources this is the MCS for any 3 cyl Suzuki engine from 85-88. Prices range anywhere from $108-$279. All of these claim to be brand new units. All sources depict a photo of the same exact unit. I was told by a few here at teamswift, those that know the carbs well, that the unit probably would not work and good luck with the purchase. Most of the suppliers of these devices tell you the parts are non-refundable, (Many electrical devices in the parts industry are this way) such a purchase situation sways many. Of course, non-refundable aside, if you desire to get the carburetor back going what option does one have but to order and see, and then make the thing work or tear something up in the process. I chose to not give up, buy the thing, find out if it would work or if it wouldn’t. If it would not work, then do whatever it took to make it work. If my approach worked, share it here with the rest of you that periodically go on the search.

At first glance they look 100% identical. Overall specs of the metal bore are identical. Internally they are both identical. Coil resistance is identical with both in the 40 ohm range. The first noticeable differences are the Jets that occupy both ends. They are clearly not the same as the old units. My old unit had a #75 on the bottom and a #160 at the top, obvious by stamped numbers. The new one, with no stampings had both at quite a bit larger. I never obtained the exact numbers, but using drill bits as reference could clearly see a difference. Obviously such a difference brought up concerns. If an orifice for flow is set at a certain value in the form of a jet, then obviously it is set at that for a reason. Or so common sense would lead most to think. I did successfully disassemble the old unit to see if those jets could be removed. Also, to learn more about how the internals of this device worked, and could the DIY rebuild one if they wanted to.

Here is what I found on the disassembly. The jets are installed using red Loctite. Red Loctite can only be loosened in one way that is to apply heat. Obviously as heat is not exactly a friend of electronic coils there was concern. Looking at the metal bore one see’s two areas, one at the top and one at the bottom that looks to be a beefier ring type area.

Image

Using this tougher area, I placed the MCS in a vice so as to try and not crush the thing. Also to hope that the vice would work as a heat sink to avoid any coil damage. Using a heat gun vs. a torch I was finally able to remove the jets. Extreme patience is key here, these jets being brass strip very easily. That and no one ever seems to have just the exact screwdriver by which to get them out. But, with heat and patience it does happen. If I ever were to reinstall a set I would use blue Loctite vs. the red. Here is a picture of what the insides of an MCS look like.

Image

Really not much one can DIY at all. There are two small rubber pads on each end that act as seals mounted to metal pads, otherwise it’s a piston rod, an a spring. I guess maybe the rubber pads could be replaced. In the case of mine, the piston rod itself was quite galled, leading me to believe that possibly it was binding in the bore. As for the electronic coil itself, I see no way possible the DIY would ever remove one and rewind it, if necessary, without total destruction of the metal casing. OF course, this is all for education purposes and to aid in finding out how to make this NEW, supposed won’t work/fit unit actually work. My goal was to see if these mismatched jets could be swapped out, and this much I did prove. However, I chose to just for the heck of it install the new MCS as it came with its oversized jets, worst case if I can’t tune the carb, or economy is affected, I’ll remove it and swap jets. But, different jets, is the least of this MX40’s compatibility problems. As stated first glances can be deceiving, as I tried to physically put it in place the real difference popped up, that being its ability to identically mount

Image

Image

The Original MCS has a small rubber boot that slide over the wires and provides some sort of dirt sealing at the top. This boot mounts all the way against the hard black plastic mounting tab found in the the middle of the MCS. The New MX40 has a similar boot, but larger in diameter and the plastic mounting tab has a raised area that is raised approximately 1/8” higher than the old MCS. This raise makes it so that this unit will not fit the top lid of the carb. Though the wires can be unsoldered, this raise cannot be ground down without damaging the wire housing. However, what can be altered is the carb housing itself. There is plenty of metal stock in the carbs lid to do what I planned to do. The old rubber boot is still used, that way the base factory hole stays the same. In the event someone were ever to actually find an exact replacement, leaving the base hole the same allows the use of the old style MCS, However, an o-ring would be needed to make up the depth of the new hole.

The tool I used to accomplish this was a standard drill press, set on high speed, and a Dremel 9900 series tungsten carbide cutter.

Image

I used a 4x4 with a hole drilled into it to hold the carb lid level. The stem that normally holds down the air cleaner is placed in the hole in the 4x4 and acts as a decent holding platform. Set the proper depth of the bit to accommodate the rise in the MX40’s mounting tab. Take your time and grind away.

Image

Image

Image

I also found it necessary to elongate the mounting holes slightly in the body of the MX40. Place a small amount if dielectric grease or Vaseline on the o-ring’s for the MCS and mount. Now all else goes together just like it should. My carb housing can accommodate both the old extinct MCS and the new mx40.

Image

Now came the real test, that is will it run properly. Aside from some other problems with a possible vacuum leak, etc that I won’t go into, The new MX40 performed great. Setting dwell was just the same as with the old style MCS. Even with the larger jets in the MX40 all seemed to do great. Time and MPG will tell just how compatible it is. Worst case I’ll remove it, and use the jets out of the old MCS.

The main point behind all of this was to prove that this NEW MCS, MX40 could be made to work in the Hitachi DFB306. Not a lot of effort to get it done. Does not alter the carb against using original stuff if ever found. But, this is not a task for the squeamish or totally lost in a work shop person. Ultimately you have two choices, do this or sell the car or car or carb. The best of us that still believe in carbs just can’t find a source for the OEM. DO you think you know where one is, please share your findings. It would be interesting to hear if anyone else out there ever bought one of these MX40’s and it fit perfect. I cannot vouch for the fact that all Carb lids are the same.

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Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Sat Jul 28, 2012 3:47 pm 
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Just a little over a month since this alternate MCS approach. Roughly 1500 miles of road usage and so far so good. The biggest difference I have seen is in the area of dwell (base mixture) setting. The FSM states to set dwell in the 23-27 range, though many including myself actually find the 27-30 range more effective. This new/alternate MCS has the engine running very rough/too rich at these settings. In using old fashion carb tuning techniques, that is to find the sweet spot between too rich and too lean, I find that the best running conditions are at what correlates to a dwell in the 37-40 range.

As for how it runs? about the same. Prior to this work I was in the 38-42 mpg range. Since then, and including the fact I am also running my AC near all the time, the mpg is in the 34-38 range.

These values are with an Automatic transmission and running speed limits or less, mostly highway running.

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Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Jul 30, 2012 4:36 pm 
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I have to say thats a impressing post/adventure in carb rebuilding. This has to show others how loved these little cars are. I'm very impressed with your work and thank you for this DIY fix for the viable MX40 MCS. This may save a few more sprints from the junk yard. Keep up this post. Are you going to go back to the OEM jets?How much was the dwell off , with larger jets? I'd like to know how well the OEM jets work in the MX40 MCS. Great post and awesome work!!!

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1985 chevy sprint 5speed 1.0 Mk1 (Blue). 1999 Geo metro 5speed 1.0 (Silver). 2003 XL-7 2.7l V6 AUTO (White). 2005 XL-7 2.7L V6 AUTO (Cobalt Blue). 1996 mercury cougar 4.6 auto (Goldish?). New to the family 1998 VW new Bettle 2.0 5speed (Black) Restord <--- (hers)<---- Gone to a new home. Replaced with 2003 Turbo 1.8T 6speed (black) ... In One 1986 chevy sprint ER (White) In line for a restore <---None runner <---(parts). Thats 7... So I'm under a hood alot... Why? Kuzz we love cars!


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PostPosted: Wed Aug 01, 2012 7:37 pm 
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glacierburst wrote:
I have to say thats a impressing post/adventure in carb rebuilding. This has to show others how loved these little cars are. I'm very impressed with your work and thank you for this DIY fix for the viable MX40 MCS. This may save a few more sprints from the junk yard.

It has the potential too..if nothing else a way to revive just spare carbs.

Keep up this post. Are you going to go back to the OEM jets?

I was only planning to go back to the OEM's if it wouldnt run worth a crap or the economy was way off....so far its not off enough to really justify going back in. As Ive been told many times, the automatic trannies on these old 3 bangers at best used to avg 32-36 at the very best. As mine has always been in the 36-42 range, I figure mine is doing impressive. Oh yeah I tweak things here and there to try and make it better, at times, but it seems to stay in that range. Still looking fwd to my 5 speed upgrade, or restore of my 5 speed car, whichever I finally find time to do.

How much was the dwell off , with larger jets?

I am running the dwell more in the high 30's now. I found that the factory high 20's had the mixture screw near all the way in to achieve those settings. I have it set by ear at the moment and all seems to be running just fine. 02 cycles as it should, plugs look great after a good run, economy is about the same, just off a bit probably due to the AC running non stop these days. As for smog checks, I dont have that here and cant vouch for that. But I have no doubt if you were to use this approach and try to run it using the FSM tuning specs, you would be running way too rich.

I'd like to know how well the OEM jets work in the MX40 MCS.
They should make it perform identical to an OEM MCS as internally these things are identical. Only the jets were different. If I ever decide to go back not to worry I'll post the effects....and thanks for the vote of confidence,

Great post and awesome work!!!

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Tue Sep 04, 2012 2:04 pm 
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mkc1962 wrote:
glacierburst wrote:
I have to say thats a impressing post/adventure in carb rebuilding. This has to show others how loved these little cars are. I'm very impressed with your work and thank you for this DIY fix for the viable MX40 MCS. This may save a few more sprints from the junk yard.

It has the potential too..if nothing else a way to revive just spare carbs.

Keep up this post. Are you going to go back to the OEM jets?

I was only planning to go back to the OEM's if it wouldnt run worth a crap or the economy was way off....so far its not off enough to really justify going back in. As Ive been told many times, the automatic trannies on these old 3 bangers at best used to avg 32-36 at the very best. As mine has always been in the 36-42 range, I figure mine is doing impressive. Oh yeah I tweak things here and there to try and make it better, at times, but it seems to stay in that range. Still looking fwd to my 5 speed upgrade, or restore of my 5 speed car, whichever I finally find time to do.

How much was the dwell off , with larger jets?

I am running the dwell more in the high 30's now. I found that the factory high 20's had the mixture screw near all the way in to achieve those settings. I have it set by ear at the moment and all seems to be running just fine. 02 cycles as it should, plugs look great after a good run, economy is about the same, just off a bit probably due to the AC running non stop these days. As for smog checks, I dont have that here and cant vouch for that. But I have no doubt if you were to use this approach and try to run it using the FSM tuning specs, you would be running way too rich.

I'd like to know how well the OEM jets work in the MX40 MCS.
They should make it perform identical to an OEM MCS as internally these things are identical. Only the jets were different. If I ever decide to go back not to worry I'll post the effects....and thanks for the vote of confidence,

Great post and awesome work!!!


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PostPosted: Tue Sep 04, 2012 2:32 pm 
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I am new to the Team Swift Forum, and like all of the valuable information that I have found here. A quick background of the car, I rebuilt the engine, and resealed the transmission about a year ago. I didn't touch the Carb. because it intimidated me.( By the way the carb. has 181,000 miles on it, standard shift) Last week the car left me stranded at an intersection, and I could not get it to re-start, I either flooded it in vein, from pumping like mad or something was majorly wrong. On preliminary checks the lower section had become loose from the mid section, and I could hear a minor leak after finally getting the car to start up. I rebuilt the carb, and wish that I had seen this forum before I had rebuilt the carb.
Currently the car idles, but after approx. 1 minute of idling it just stalls, no reason. I do know that the idle down micro switch circuit has been bad for awhile, so I am not convinced that this is the whole problem. ( The check engine light would come on at Wide Open Throttle no codes)( I ordered the micro switch today, as I found the link on another page on this website) However since I have to take the carb. back apart to fix the MCS. I would like to replace the following to.
1. -Carb. Float
2. -Carb. MCS. ( MX40?) solenoid
This is the only carb. Sight that I have found so far & do not see the MX40 listed
http://www.carburetion.com/search.htm
If you could post the resource for the MCS. I would appreciate it, I haven't had much luck myself.
Additionally would like to replace the float with a new one, as I can't find it anywhere either.
3.This part is totally unrelated, but noticed it needed changed out to was the Low Gear Transmission switch. I went ahead & replaced the inner CV boot because it was torn & noticed that this switch was broke. ( This explains why the Shift up light quit working) I can only guess that something got caught on the Half shaft rolling down the highway. Thanks any help would be appreciated.


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PostPosted: Tue Sep 04, 2012 6:49 pm 
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how is your EGR valve ..?


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PostPosted: Tue Sep 04, 2012 7:02 pm 
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The EGR Valve has been disconnected for years. ( I was in search of a vacuum leak & never reconnected it. ) Secondly , you can actually watch the flow of fuel stop, just before the engine turns off, I believe that the MCS, is either intermittently shorting out, or internally binding up.


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PostPosted: Wed Sep 05, 2012 5:40 pm 
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87chevrolet wrote:
I am new to the Team Swift Forum, and like all of the valuable information that I have found here. A quick background of the car, I rebuilt the engine, and resealed the transmission about a year ago. I didn't touch the Carb. because it intimidated me.( By the way the carb. has 181,000 miles on it, standard shift) Last week the car left me stranded at an intersection, and I could not get it to re-start, I either flooded it in vein, from pumping like mad or something was majorly wrong.

If this ever happens again. Try holding the pedal to the floor vs all that pumping. But regardless sounds like you had quite an impressive vac leak.

On preliminary checks the lower section had become loose from the mid section, and I could hear a minor leak after finally getting the car to start up. I rebuilt the carb, and wish that I had seen this forum before I had rebuilt the carb.
Currently the car idles, but after approx. 1 minute of idling it just stalls, no reason.
Try increasing the idle speed to keep it running, then proceed with some serious vacuum leaking checking. I find that removing ALL vacuum hoses, Blocking off all vac ports, then reconnect each one, one by one, the guilty one usually will cause the engine to stall. Like JVS stated the EGR is often a culprit. But if yours is blanked off...It is blanked off right. Not just disconnected? If still there it could still possibly be a source of a leak at its base.

I do know that the idle down micro switch circuit has been bad for awhile, so I am not convinced that this is the whole problem. ( The check engine light would come on at Wide Open Throttle no codes)( I ordered the micro switch today, as I found the link on another page on this website) However since I have to take the carb. back apart to fix the MCS.
I would recommend searching for vac leaks prior to assuming the MCS is the culprit.

I would like to replace the following to.
1. -Carb. Float
2. -Carb. MCS. ( MX40?) solenoid
This is the only carb. Sight that I have found so far & do not see the MX40 listed
http://www.carburetion.com/search.htm

You can try, http://www.rockauto.com or http://www.walkerproducts.com. Most Oreilly auto parts carry walker items. There are also several other web sources for the MX40. If memory serves me I got mine from Rock. Walker claims that they had an exact replacment MCS. However, I actually spent a few hours on the phone with a rep from that company. He pulled all of the items that they show fit the early sprints and none did NOT have the lip I was forced to machine out up above. Walker's prices are a bit high as well. That being said I opted for the commonly found $109 unit (mx40). When I get h ome tonight I will try to be exact on my source jsut cant reach much form here at work.

If you could post the resource for the MCS. I would appreciate it, I haven't had much luck myself.
Additionally would like to replace the float with a new one, as I can't find it anywhere either.

Walker or Oreilly will have that.
3.This part is totally unrelated, but noticed it needed changed out to was the Low Gear Transmission switch. I went ahead & replaced the inner CV boot because it was torn & noticed that this switch was broke. ( This explains why the Shift up light quit working) I can only guess that something got caught on the Half shaft rolling down the highway. Thanks any help would be appreciated.


Another suggestion. You constantly read about folks having torn boots on cv shafts either right after replacing or even right after a new shaft assembly is installed. Not to say your was that way. But Many of these boots and shafts have sat on shelves for god knows how long. Rubber gets a bit stiff as it ages. Start to flex it a lot and it will tear. CV shafts definately flex. Power steering fluid is specifically designed to aid in keeping rubber seals pliable. If you will take the time to coat your boots in PS fluid prior to any replacement, you will find that they will last a very long time. Apply several heavy coats to the outside of the boot, similar to the way you would apply numerous coats of say armorall or similar to faded plastic. You will notice the that the rubber will actually absorb a lot of it. After several coats over a period of say an hour wipe off the excess and install the boot. I had a friend that used to professionally restore old vehicles and such for a museum that shared this tip with me over 20 years ago. Since that time I have rarely had a premature boot failure.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Wed Sep 05, 2012 5:50 pm 
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87chevrolet wrote:
The EGR Valve has been disconnected for years. ( I was in search of a vacuum leak & never reconnected it. ) Secondly , you can actually watch the flow of fuel stop, just before the engine turns off, I believe that the MCS, is either intermittently shorting out, or internally binding up.



What do you mean you can see fuel flow stop?...bowl window goes empty? You do realize the MCS controls Air flow not fuel?.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Wed Sep 05, 2012 8:29 pm 
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Location: Eaton Ohio
mkc1962 wrote:
87chevrolet wrote:
The EGR Valve has been disconnected for years. ( I was in search of a vacuum leak & never reconnected it. ) Secondly , you can actually watch the flow of fuel stop, just before the engine turns off, I believe that the MCS, is either intermittently shorting out, or internally binding up.



What do you mean you can see fuel flow stop?...bowl window goes empty? You do realize the MCS controls Air flow not fuel?.


O.L. I did notice that the fuel level was to hi, in the glass window. (I have to pull the carb & reset the fuel level) During the idling of the engine I seen a light spray of fuel from one of the upper jets, I thought that this was the injection of fuel from the solenoid. Am I wrong on that operation? I thought that the MCS injected fuel sort of like a fuel injector, if its' not, then I still would prefer to replace the MCS because I spent most of the day Sun. putting the complicated thing together. I don't want to have to take this carb. off a 3rd time. I want it to be fixed after the 2nd time. That is why I decided to go this route, that & this car is my daily driver. As for the EGR, the EGR valve vacuum port I just plugged it off. I will probably just go ahead & order an EGR valve & gasket since I am in that area just in case. The only other possibility would be the vacuum booster and it is a 1 year old reman. unit. That is the only other thing that I haven't tried to block off. It looks like this next weekend is going to be busy.


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PostPosted: Fri Sep 07, 2012 8:06 pm 
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Quote:

O.L. I did notice that the fuel level was to hi, in the glass window. (I have to pull the carb & reset the fuel level)

Proper fuel level is at 1/2 site-glass with engine running. Yes proper level is very crucial to proper running. Personally I like to set mine while level on the work bench. If its right there, its right on the engine.

You say your new to TS. Here is the advice a dozen or so of us will give you, I cant believe i have beaten Phil to it...If your going to own one of these cars, work on it yourself, and have it running proper you really need to obtain a Factory service manual...Not a Haynes or Chiltons but the OEM chevrolet manual. Do a search on ebay they are commonly found for under $10. Things like this topic of fuel/air flow and hundreds of other topics are clearly explained there. You will get all sorts of help here if you show that you have made some effort to learn some of it on your own. We all started that way.




During the idling of the engine I seen a light spray of fuel from one of the upper jets, I thought that this was the injection of fuel from the solenoid. Am I wrong on that operation?
Yes, fuel can be seem when looking down the bore coming from one of the small pipes. But no, this is not being forced out by the MCS. Engine vacuum along with air mixture facilitate this flow. The MCS controls air flow.

I thought that the MCS injected fuel sort of like a fuel injector, if its' not, then I still would prefer to replace the MCS because I spent most of the day Sun.

Suit yourself. But unless you find the cause of your stumbling and take dwell readings on the MCS during running you wont be accomplishing anything.

putting the complicated thing together. I don't want to have to take this carb. off a 3rd time.

I Know you hate it....we've all been there. But unless you know the thing inside an out and understand why its doing what its doing. along with knowing for a fact that the MCS is operating properly and the micro switches are set proper, and all the other parts and pieces of the carb are doing what they are supposed to do...The your just wasting even more time. Yes they can be overwelming and complicated, But anyone with Patience AND the FSM can handle it. But then there are some that never can. The Hitachi carb and lack of patience is why so many of these little jewels hit the junkyards. I am not trying to discourage you, I am trying to help you follow the path in the correct direction.

I want it to be fixed after the 2nd time. That is why I decided to go this route, that & this car is my daily driver. As for the EGR, the EGR valve vacuum port I just plugged it off. I will probably just go ahead & order an EGR valve & gasket since I am in that area just in case.

Well that or make a plate to completely block it off. But, it is there for a reason. Also if your in a smog testing state I cant vouch for your ability to pass without it....either way it can be a source of a vacuum leak even if unplugged.

The only other possibility would be the vacuum booster and it is a 1 year old reman. unit. That is the only other thing that I haven't tried to block off. It looks like this next weekend is going to be busy.

Like i Suggested earlier. remove ALL vac hoses from the carb and intake. Plug all ports. IF the carb is properly built it will run just fine without all of the hoses connected. But you may have to idle it up. If its idling rough with no hoses connected, then you probably have some sort of leak in the base gasket. Once smooth idling with no hoses, then 1 by 1 connect each hose. Pay attention to what each one does or doesn't do to idle.....Just for the heck of it, IF you get it to idle fine with no hoses, at this point you can check your dwell of the MCS. Checking Dwell of the MCS is the only known way to determine if its any good or not. Search the forums, I wrote a very long thread on the topic of Dwell some time back.


_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Sep 10, 2012 11:51 pm 
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Many things can stop these cars dead. I doubt it's the MCS because these can rarely stop a car from running. I doubt it's a vacuum leak because your issue seamed intermittent and you said it absolutley won't start when it happens. I had a float stick once in one of these carburetors causing the float bowl to go completely dry thus making the car not start. The only time you should see mist coming out of the venturis on these carburetors is when you open the throttle.

Maybe I am going over the same things here but, Have you checked your float level. There is a tiny sight glass at the front of the carburetor by the throttle switches. The fuel level should be at the white dot on the sight glass at all times. sometimes rocking the car back and forth helps to reveal the fuel level in the sight glass.

Have you checked for vacuum leaks? spraying starting fluid at a potential leak source will cause a change in engine speed if there is a leak.

When the car is idling, if you spray carb cleaner or starting fluid in the throttle bore does the engine briefly rev up or slow down?

Maybe this should continue on in another thread, because MKC1962 just got his topic hijacked.

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PostPosted: Tue Sep 11, 2012 9:15 am 
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Stampy wrote:
Many things can stop these cars dead. I doubt it's the MCS because these can rarely stop a car from running. I doubt it's a vacuum leak because your issue seamed intermittent and you said it absolutley won't start when it happens. I had a float stick once in one of these carburetors causing the float bowl to go completely dry thus making the car not start. The only time you should see mist coming out of the venturis on these carburetors is when you open the throttle.

Maybe I am going over the same things here but, Have you checked your float level. There is a tiny sight glass at the front of the carburetor by the throttle switches. The fuel level should be at the white dot on the sight glass at all times. sometimes rocking the car back and forth helps to reveal the fuel level in the sight glass.

Have you checked for vacuum leaks? spraying starting fluid at a potential leak source will cause a change in engine speed if there is a leak.

When the car is idling, if you spray carb cleaner or starting fluid in the throttle bore does the engine briefly rev up or slow down?

Maybe this should continue on in another thread, because MKC1962 just got his topic hijacked.


A lot of good advice; consider this:
-an MCS can stop a Chevy Sprint dead in its tracks. Few other things can do this, but in general:
a.)Mechanically, a broken timing belt might do the same.
b.)Electrically, a problem in the distributor, or secondary wiring might also cause a quick but temporary death.
Most other problems will let you know in advance, so you have a chance to repair them.
-not all sight glasses have a white dot.

The point is, the Forsa/Sprint/Firefly NA is very reliable.

Getting back to the MCS, it is still a difficult part to find and a good one to stockpile.
Modifying the carb body top is but one way to adapt so you can use the more readily available parts currently available and the gist of this thread.

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Once you get the cars dialed-in (compression, leaks, bearings, alignment, brakes) swap in new rubber and glass, you've got something which should last for years!


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PostPosted: Wed Sep 12, 2012 10:26 pm 
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Location: Eaton Ohio
O. K. I haven't gotten to the carb. last weekend, so I am hoping to this coming up weekend. Just so you know, I do have an OEM Chevrolet Service manual, I bought it 2 years ago. It is full of great information. Secondly my shipment of parts did finally come in. My MCS, Float( I am not sure it is the correct one it is a Standard P/N FL65. It has an appendage at the end of the topside that rises up, where as the original one did not) I got my two Micro switches, ( I know for a fact that the idle one is bad) .

Now, after I get the car back to running proper, does anybody know if you can still find, or adapt a switch to work for the three wire transmission shift switches??? One of mine has bit the dust, and judging by the looks of the other one it isn't long for this world either before the wires break away from the switch.


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PostPosted: Sun Sep 16, 2012 12:40 pm 
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O.K. I am working on Carb. rebuild # 2 ( second attempt) it turns out that the problems are ads follows, (1) fuel level to hi, (2) Faulty Micro Switch, (3) Napa rebuiltd kit only comes with 2 throttle plate gaskets- can one be modified to work?


Sixth: One very unusual problem I've run across is the gaskets under the carburetor. There is supposed to be an insulator below the carburetor (thick piece of 'plastic'). Above and below it are two DIFFERENT gaskets. Recently, someone was having problems with their car, and no amount of PMs could repair the problem. When I took off the carburetor, I found that the local mechanic had used the gaskets in the generic rebuild kit, but had put two of the same gaskets on the insulator - one above and one below. Again, the insulator should be fitted on the intake manifold with two DIFFERENT gaskets.


I am working on this today, please reply with responses, meanwhile I will be setting the float level by allowing gas to flow into the carb. & by re-wiring & installing replacement micro switches, and MCS Valve. Have a great day & thanks for all of the advice. Additionally please respond to my above post question about the float, and the transmission switches. If the replacement float won't work I will re-use the old one.


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PostPosted: Sun Sep 16, 2012 11:01 pm 
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Cant tell you anything at all about that trans switch.

as for the float # also not a clue, I have not ever bought a replacement. But as you have the original, compare the new one to the old one. as for setting the float. Yes with actual gas, on the bench, level as possible is the best way. No need to screw down the lid just put the gasket in place and sit the top down as it should be, shoot for 1/2 glass.

As for your base gaskets. If your kit does not have the proper one then modify what you have or get some gasket paper and make one.

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Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Sep 17, 2012 12:29 am 
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Location: Boise ID
New to the board and probably won't post a lot, but found something that may be of use. We own an '88 Sprint that we keep for a commuter, and I managed to find another option for the MCS. The company that has them is called The Carburetor Refactory and they're in Richmond CA. Their part number for it is MCS-18. It's a direct fit with no modifications to the carb top necessary. It also fits the '86-89 Sidekick or Samurai with the 1.3. It's not the same at the top as the MX40 that I've seen other people use.

I had a conversation with the owner about the fitment, and he says yes, the jets are slightly larger than the original Sprint jets. However, the top jet is an air bleed, and the lower jet is the main jet, and the relationship between the two as far as percentage of flow, is the same as the Sprint carb. Since it's a feedback unit, the computer will adjust duty cycle to get the A/F ratio it wants, it will simply be slightly biased to a lower duty cycle than the OEM MCS. He's been building these carbs for quite some time and says the original Sprint MCS is long gone.

I installed the MCS-18 in our carb this morning, and it cured the driveability problem we were having which was surge at cruise. I had leaned out the mixture screw all the way in order to get it to idle, and was sure the MCS was internally stuck. I can also now get a dwell reading out of it, which I couldn't before. It drives like it should now. We were pretty sure ours was stuck in a way that was allowing too rich of a mixture.

The cost for the MCS-18 was $129. If you send off your Sprint carb, they'll rebuild it for $480 and that includes testing everything and they always replace the MCS the owner says. Also re-doing the accel. pump is included. Wish we'd found that earlier, as I'd sent it off to a major rebuilder down in FL that charged us $199, and then I've had to have it apart 2 more times to repair what they didn't. Finally fairly happy with how it runs again. Really wanted our 50MPG car back!


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PostPosted: Mon Sep 17, 2012 7:02 pm 
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Location: Eaton Ohio
O.K. can anyone post a picture of the two different gaskets, and show what ports need to be connected where? I seen one that curves around the secondary, to a screw hole. but there is no place for the small hole that I found on the primary base area in the primary circuit.

If anyone doesn't have a source for a replacement float, then I am stuck re-using what I have got, after about 3 adjustments the fuel is sitting directly in the center when gravity fed. I am convinced that the next time the Carb. has to be removed that I will have to replace the float because I believe that the float is saturated with fuel, and don't know how long it will last this time, this could be what caused my problems in the first place. HEY TRAVELLER, do you suppose you can ask one of the Carb. re-builders where they are finding the Carb. Float at? I would like to purchase 1-2 for future use. Most of the auto part warehouses aren't being of any help around here. They look at you with a blank stare & say, our computer doesn't go back that far.


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PostPosted: Mon Sep 17, 2012 8:36 pm 
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There should be a Napa part number for that float in one of my posts.

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Once you get the cars dialed-in (compression, leaks, bearings, alignment, brakes) swap in new rubber and glass, you've got something which should last for years!


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PostPosted: Mon Sep 17, 2012 9:23 pm 
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I was looking at the page: Hitachi DFB306 carburetor woes...( page 2 ) http://teamswift.net/viewtopic.php?f=22&t=53897&hilit=insulator&start=25 I was looking at the gasket setup for this vehicle, mine is identical to this, except that it is for a Chevrolet sprint what modifications do I need to do to make this gasket work?


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PostPosted: Tue Sep 18, 2012 12:01 am 
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Sorry don't have any pics or actual gaskets to photo....the one with the arched loop in it goes beneath the insulater against the intake.. The other goes on top against the carb.

Your FSM should clearly show the proper placement.

TRAVELLER,

shame you didn't take a picture for comparison purposes. I know I spent over 2 hours on the phone several months back with WALKER manufacturing, comparing every unit they had for identical compatibility and they didn't have anything that was identical. Though I did what I did, I can still use the exact if found. There are many of us here that would truly love to find the exact fit, but many have tried and never found. Would really like to hear some feedback from you on the Dwell setting you went with along with your MPG results after a few tanks.

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Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Fri Sep 21, 2012 12:15 am 
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Location: Boise ID
mkc1962 wrote:

TRAVELLER,

shame you didn't take a picture for comparison purposes. I know I spent over 2 hours on the phone several months back with WALKER manufacturing, comparing every unit they had for identical compatibility and they didn't have anything that was identical. Though I did what I did, I can still use the exact if found. There are many of us here that would truly love to find the exact fit, but many have tried and never found. Would really like to hear some feedback from you on the Dwell setting you went with along with your MPG results after a few tanks.


It looks externally identical to the OEM one which is what I removed. The jets are not marked for size unlike the OEM version which had the 160 air and 75 main jets. The wire terminals are flat blade style, so they wouldn't work on my '88 which has the round pins in the 6 pin connector. I used the good butt splices that shrink to fit when heated, then seal. We drove it around town after the repair and it's MUCH improved as far as driveability. Did find one thing I wasn't happy with though. The previous rebuilder didn't replace the disc on the accelerator pump from all appearances. I'm REALLY not happy with the rebuild. About the only thing they did was clean everything and put it all back together with a new float and gasket set. The old MCS appears to be stuck.

Set the dwell on 25. The mixture screw is about 3/4 of a turn out from where it was before, and it fired right up and ran great with no issues after the fix, so I knew that it was improved. The surge at part throttle cruise at 45, 55 and 65 MPH is gone, so I'm sure that was the problem. We'll have to see what the mileage will be after a couple tanks. It was getting 40 commuting with the MCS not working, but would sometimes hit 52 on a 150 mile round trip. Only if you kept driving it and didn't do much town mileage, as it would load up because the float level would go too high.

If nothing else, it certainly runs a ton better. One issue cropped up the other night though. Now the water pump has decided to leak. I have a new one for it, just not looking forward to pulling the timing cover off and putting the new pump on. I think that's about the last thing that can be replaced on this car. It's in great mechanical shape otherwise. I'll be changing the pump this weekend and then one of us will commute with it for a week to see how it does. Maybe take a trip with it in a couple weeks. Thinking Boise to Spokane to visit some friends. That's an 840 mile round trip, so should get a good idea of mileage.


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PostPosted: Fri Sep 21, 2012 12:21 am 
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Location: Boise ID
I can find the float right away on the NAPA website. I have one that I picked up just in case. CRB 2549 is what it shows. $12.17. I grabbed one just in case the needle and seat wasn't the cure for the first problem I had, which was the fuel level drifting too high after the rebuild. Worked good for a couple weeks (the fuel level, nothing else was right) then it changed.


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PostPosted: Fri Sep 21, 2012 4:40 pm 
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Thanks for the feedback and explanations. As for the accell pump. All the kits I have obtained from either Rockauto or Oreillys have had the complete accel pump in the kit. I always make sure that a kit I buy does have it. However, there are also lesser kits that don't.

Be interested to here of your mpg results with the settings you have after a few tanks.

All this summer after my above mod I have run a consistent 36-37 mpg. But my car does have the Automatic trans, and most of teh summer was with the ac on and still occasionally is.. With the old MCS I was avg 36-40. 36 was the best that an automatic performed back then. to do 36 with today's fuel is probably a better accomplishment.

To run mine with the factory dwell specs in the mid 20's drops my economy down to 30-32. With this new MCS, Dwell that fluxuates from 35 upward nets me the best mpg. IF I go as high as 37 as the low and upward from there once again it drops. I personally have never seen an MCS that would do more than 56.

I run the timing at factory 6 deg.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2016 Outback, 06 Expedition, 87 Porsche 911, 87 Turbo sprint, 82 Brat, 73 gmc 4x4, 69 camaro, 99 Gl1500 Honda Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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