Flat spot in acceleration? Metering rod jet

joebuck · Post by **joebuck** » Tue Oct 22, 2013 10:17 am

troubleshooting my manuals for the cause of a flat spot in acelleration, i took the metering rod housing off Carter Carb. well something sounded like it click! drop...not sure...but when reasembled I didnt notice a metering rod jet?.....it looks threaded so could it have pulled out when i pulled Metering rod housing and components out?

reasembled and jeep still runs exactly like it did , for what that is worth

also booklet said cause could be "worn or damaged plunger leather" what and where is that?

Post by **wesk** » Tue Oct 22, 2013 10:25 am

You should tell us what model jeep and/or carb. Sounds like you are talking about the WO or YF civvy carb. No leather in a M38 or M38A1 YS carb.

joebuck · Post by **joebuck** » Tue Oct 22, 2013 10:27 am

1952 m38 carter model y-s 637s

joebuck · Post by **joebuck** » Tue Oct 22, 2013 10:37 am

i see in my booklet the metering jet is screwed in.....but how would i adjust the metering rod?

Post by **wesk** » Tue Oct 22, 2013 11:27 am

Then my next question is what book are you using? There is no leather in a YS637S.

The seat for the metering rod is item AA in this illustration and it is threaded into the carb body. Perhaps what you hear drop was the retaining pin item EE that connects the metering rod to the metering rod diaphragm.

joebuck · Post by **joebuck** » Tue Oct 22, 2013 11:44 am

I am using the Ordnance Maintance Carburetors ( Carter) Excerpts ( Carter model y-s 637s for M38 1/4 ton)

on page 28 under Trouble Shooting

e. Engine Falters or Pops Back through Carburetor on Acceleration
(2). Worn or damaged plunger Leather. Replace Plunger.

where is plunger?

EE.... i think you are right!!... let me tear it down again and see....

Post by **wesk** » Tue Oct 22, 2013 11:57 am

Be careful using the illustrations in that manual. The blowup in that manual shows the metering rod spring on the wrong side of the diaphragm.

The troubleshooting pages are generic to all Carters covered by the manual. The plunger leather being referred to is the acclerator pump plunger in the WO series and the Ball & Ball series Carters.

As an aside the acclerator pump in your 637S is also vacuum operated and if that diaphragm is deteriorated or punctured/perforated it will also cause a flat spot in acceleration.

joebuck · Post by **joebuck** » Tue Oct 22, 2013 12:01 pm

thanks Wesk......i did lose that EE pin.... i guess i could fabricate one from a brass tack or something couldnt I?

just reread your post......you are right.... the spring was on different side......i will flip around and have spring on diapragm to give it pressure.......thats probably my flat spot!!! fingers crossed... thanks so much Wesk!! off to hardware store to make a brass pin.....gave up trying to find in my drive way

wilfreeman · Post by **wilfreeman** » Tue Oct 22, 2013 5:45 pm

Hey joebuck,

Make sure you follow up with your outcome. This is the type of info that we need on the forums. There are alot of people that ask for help here, then we never here another word about the outcome. Thanks for your help in this matter.

joebuck · Post by **joebuck** » Tue Oct 22, 2013 5:53 pm

Winner winner chicken for dinner......it worked... No more flat spot. Previous owner had the spring on wrong side of metering rod just like Wesk said. he had apparently assemble carb like the manual I listed. ( which he gave me) showed a pic . But it was WRONG............. Still learning how to adjust carb to lean screw to maximize out put but this spring reversal took me from 48 to 54mph...yahoooooo

wilfreeman · Post by **wilfreeman** » Tue Oct 22, 2013 6:08 pm

COOL! Thanks for the followup Joe, and for the suggestion Wes. Now, would this happen to apply to the M38a1 also? I just rebuilt my spare carb a few months ago and have a flat spot also. I done remember if I used the manual or just put it back together like it came apart. I might just have to pull the cover off and check it.

Post by **wesk** » Tue Oct 22, 2013 8:04 pm

Although the A1's YS950S carb has a larger bore it's circuits are almost identicle as are many of it's parts. The metering rod has a different part number but it all goes together the same way and the same mistakes on the spring location will yield the same symptoms. Don't forget what I said above about the affect a bad accelerator pump has on acceleration. Both are vacuum operated and both are sensitive to diaphragm deterioration.