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I am looking for a carb overhaul kit for my M38. Several years ago I purchased two kits from a well known MV parts supplier.... that did not fit very well at all. The gaskets and the diaphrams were all off enough that I could not use them at all. I trashed one kit and tossed the other up on a shelf. Bad experience. I paid $50.00+ dollars for them also.

Now...who has any experience with purchasing an overhaul kit that actualy fits. That the gaskets are manufactured so that they line up properly with the carb castings and the diaphrams will fit without stretching and tearing?

Recomendations? Anyone?

There's only three vendors selling the modern kits. Midwest Military, Army Heep Parts and Ron Fitzpatrick's Jeep parts. I've used both kits and they work just fine.z

The kit I bought from Midwest Willys was installed in a carb for a M38A1, still running well 3 years later.

OK...I needed to hear THAT... I have two M38 carbs to rebuild now,,,and did now want to get stung again...Thanks.

The kit from MWM and AJP is a dual service kit in that it contains both M38 and M38A1 parts to rebuild one carb.

The G503 Ron F kit is model specific.

Both use modern rubber parts.

Remember when rebuilding the M38 (YS650S) carb the illustration of parts in the TM 9-1826A shows one diaphragm spring in the wrong sequence. Also since the TM 9-1826A was printed in 1952 it does not include the illustrations, part list and specs for the M38A1 carb (YS950S). I have included them in the manual exerpts on our downloads page and have included a corrected drawing of the YS637S.

A caution on parts. Though both carbs are similar the 950S has the larger bore and throttle plate, it's throttle body is indexed differently from the 650S and it's porting between the throttle body and the bowl is different ad are it's metering rod and diaphragm springs. So be careful and layout your old parts neatly to use as an aid in ID'ng correct new parts.

Thank you. All very good and useful information.

I don't see anything re M38 carbs in the downloads section...am I not seeing it?

Again...thank you.

I have received my carb kits, two of them from MWM @ $55.00.

Allow me to air some problems and questions I have about these, made in India... available... carb kits and the YS carb.

Here are some common problems I am finding with these carb kits.




NOW...for the record...which side of this diaphram does the spring go on?


In fig #58 0n the PDF for the YS carb...an illustrated cutaway view...the spring is illustrated as being between the diaphram and the cover. Like THIS:




And which spring goes where...there appear to be three different springs with the kit...


Thanks any help would be usefull in the extreme.

This is why I said to use caution with your dis-assembly and to lay out your old parts carefully. I also pointed out an error in the TM 9-1826A diagram on one spring location. The copy of the pertinent parts of that TM included my doctored illustration which places the springs in their correct locations. The simple answer to the spring positioning is "ALWAYS PLACE THE DIAPHRAGM SPRINGS BETWEEN THE DIAPHRAGM AND THE LID.".

I agree the workmanship/quality control on the diaphragms is poor but I see no reason why they wouldn't function just fine.

The softer spring rate goes with the metering rod and the harder spring rate goes with the accelerator pump. I also believe the 637S uses a shorter accelerator pump spring than the 950S.

I appreciate the extra effort being taken with this topic. I will be rebuilding two YS M38 carbs which have BOTH apparently been assembled incorectly...by persons unknown/former e-bay owners?

I am going to have to modify the diaphrams to get a correct...wrinkle free...stretch free...fit between the main body of the carb and the diaphram cover. It seems that by enlarging the one hole...it/they, can be made to fit in an acceptable, leak free manner.

Now to mount it and give it a try...SUCCESS! My pea shooter flathead idles fine and seems to have good power.

I just finished rebuilding the second M-38 Carb using the other carb overhaul kit from MWM. I expected a poor fit of some parts..as in the first kit I used. This was not the case. The second kit...well...the parts fit well enough that it was an easy rebuild. I wonder why the two kits were/are so...different.



On THIS carb...on teardown...for overhaul, the diaphragm for the accelerator pump was mostly...disolved. I looked as if the rubber product bonded into the fabric of the diaphram...just..disolved.
Must be this wonderful new fuel that is keeping us all from melting from global warming. ???