YS Carb Rebuild

blaze · Post by **blaze** » Sun Feb 13, 2011 10:38 am

Hi Everyone. Still at it . My engine started and ran till the gas ran out that I poured down the carb. It seems that the carb is not pumping any fuel into the engine. I removed the line to the carb and cleaned a very clogged filter. I reconnected the line and tried pumping the accelerater,but no sign of fuel. I then removed the top of the carb and there was fuel in the float chamber. This tells me it is time for a rebuild. Does any one have a diagram for a ys carb ? The kit I purchased does not have a breakdown sheet included.This would be my first attempt to rebuild a carb.

Blaze

MODIFIED · Post by **MODIFIED** » Sun Feb 13, 2011 3:06 pm

This Carter YS rebuild manual is found in the "Download" section:

http://www.willysmjeeps.com/downloads/YScarb.pdf

-play close attention to the proper location of either pump springs.
-correct float setting for M38A1 Carter YS 950s carb is 9/64"
-correct float setting for M38 Carter YS 637S carb is 1/4"

Make sure you check for vacuum leaks at base of carb when re-installing to motor. good luck

Cacti_Ken · Post by **Cacti_Ken** » Sun Feb 13, 2011 4:49 pm

On the YS carb., It doesn't do any good to pump the accelerator pedal to get gas in the throat nor actuating the butterfly on the carburetor because it doesn't have an accelerator pump in the carburetor.

GPA · Post by **GPA** » Mon Feb 14, 2011 1:26 am

It does have an accelerator pump, but it is vacuum operated.

blaze · Post by **blaze** » Mon Feb 14, 2011 10:07 am

Hi Guys
Can't thank you enough for your input and technical assistance. It sure gives one confidence to see that we can tap in to so much knowledge and most of all the willingness to help strangers with the same hobby. Again special thanks to all.

Blaze

Post by **wesk** » Mon Feb 14, 2011 2:20 pm

Blaze,

You said the filter was plugged up. This means you have trash in your fuel system. You will need to resolve that issue first. It may be that enough of that trash has entered your carb and plugged up the small passageways in it.

If this is true then fix the trash issue first which most likely is corrosion in the tank. Then make sure the pump is delivering fuel at at least 2.5 PSI. Then clean out the carb and blow the passageways to make sure they are not plugged. Then reassemble the carb and try running it.

In the illustration below from the carb rebuild manual I have corrected the positions of the two springs that operate the diaphragms. Be sure you use this diagram or the one from the M38/M38A1 parts manual.

As mentioned above, unlike the civvy carbs the accelerator pump you are used to seeing squirt gas into the throat of the carb on the civvy carbs will not on the M38/M38A1 carbs. They use a vacuum operated accelerator pump and they also use a vacuum operated metering rod.

DanS · Post by **DanS** » Tue Jul 17, 2018 4:29 pm

So Wes;

What was the correction in the diagram? I am having trouble with my newly rebuild M38 carb. It floods very easily. Please advise.

Dan

Post by **wesk** » Tue Jul 17, 2018 11:11 pm

The diagram of the YS637S in the Carb TM 9-1826A (Fig 60 page 114) shows the metering rod bellows spring (Item BB) between items AA & CC whereas it belongs on the outboard side of the diaphragm between DD & FF. This is the illustration with my edit:

AFB · Post by **AFB** » Sat Oct 02, 2021 12:18 pm

Wes, Thankyou fort admitting me to this board there looks to be a lot of info on here, I'm bringing up an older post on these YS carbs, I just rebuilt one on an M38 and needed it to go for a quick show but I have it back in the shop as it doesn't want to run at just above an idle unless you pull the choke out about 1/2 in, above an idle it runs good and at idel it runs well, and it seems to stumble upon acculartion then clears out I'm guessing a vacume leak but did not think to check for that before I pulled the carb off, but what did bother me was there is a port on the top of the fuel bowl on the opoisite side of the ball and weight with a keyhole looking indention leading to it, I have tried blowing air thru it but it doesn't come out any other opening, it seems odd that the port would be there and not go anywhere, am I missing something.

Thank you
Aaron

Post by **wesk** » Sat Oct 02, 2021 10:46 pm

The fuel bowl has a vent port on top that attaches by tubing to the air induction crossover pipe. This port must remain unobstructed for proper ops of the carb.

AFB · Post by **AFB** » Sun Oct 03, 2021 10:04 am

Thanks Wes I'll try that, I think i may have found a problem I had the orface with the check ball in it was stuck, I did not replace it when I rebuilt the carb, reason being was that the other orface that screws in at the metering rod was not made the same as the orginal, it was longer and did not fit so I used the old one there and just used the old one in the acc pump also.
I'm still wondering about the drilled port that seem to go nowhere on the edge of the fuel bowl opisite side of the check ball and weight.

Post by **wesk** » Sun Oct 03, 2021 5:59 pm

If you review the TM 9-1826A dated DEC 1952 closely you will note that pages 108 thru 112 have very detailed passageway illustrations.

You can download PDF copy of needed sections on our downloads page. Also I have the illustrations loaded in my photo album under the M38 Fuel System where you can review them. It helps to be able to read the narratives that are there to walk you thru each illustration.

Here's an example:

AFB · Post by **AFB** » Mon Oct 04, 2021 7:43 am

Thanks Wes, I had looked thru those and didn't see the port I'm asking about but I'll go over them again, but its starting to look like its a go nowhere port on this carb, as the corresponding matchup in the air horn does nothing either, I'm wondering if it is for a different applacation.

Post by **wesk** » Mon Oct 04, 2021 8:52 am

A picture is worth a thousand words!!!!

Post a photo of the two faces and mark the hole you are curious about.

keats · Post by **keats** » Mon Oct 04, 2021 9:50 am

I believe there are two versions of the m38 carb. one does have an unused port . the outside castings are different. Wes has photos of these two casting somewhere I'm sure, as I bought them up to him years ago.