M38 Cdn Carb Help

[Peter Phillips]

Thought I'd try this community to help troubleshoot my carb issues. Here's the situation:
1. Jeep wouldn't idle when coming out of hibernation but "ran when parked".
2. After talking to the PO, it was determined that the existing carb rebuild was over 10 years old but still worked OK last Fall.
3. I had a NOS kit from Brian Asbury which I installed after blowing out all the ports etc with carb cleaner and compressed air.
4. I set the float to 1/4" with a homemade cardboard gauge across the carb top with the float resting on the needle and spring.
5. Air idle screw set to 1 turn out.
6. I checked the delivery from the fuel pump and it seemed to fill a mason jar easily while cranking.

Still wouldn't idle but seemed to run fine with the choke almost completely closed but very rich as you can well imagine. The throttle response is very crisp when it does run.
Here's where I really started grasping at ideas including a few more tear downs and full blow outs and even resorted to swapping back to the original needle and seat and re-adjusting the float height.
I even ran it through the ultrasonic cleaner to see if that would help.....nada.
I'm outta ideas here folks. I'm no stranger to carb work and I've tried all my tricks to no avail.
I do have a parts carb that I may clean up and try...can't hurt.

[Mike Kelly]

I guess this is a original Carter ?

There is a guy on the G503 forum (scoutpilot)) who runs a business, he rebuilds these , he knows more than any of us will ever know. He will freely offer advice.

Is the throttle shaft worn ? A slight slop in the shaft and air will be sucked in. This air leak upsets the idle citcuits.

Also, a inlet manifold air leak ?

Have you seen this https://oldjeepcarbs.com/

Edit. Looks like a YS Carter was fitted. The old gaskets from a NOS kit will have shrunk , might not be sealing ?

[rob love]

A common problem I run into on the Jeep carbs is that, with todays ethanol poisoned fuel, those two little diaphragms on the front and rear of the carb will crack or puncture and you will not get a good running engine. Usually though, that is more of a flooding situation. I have had better luck with the ethanol resistant kits from places like midwest military, but even better is to stay away from the ethanol fuel as much as possible.

Note there are also conflicting illustrations in the manual on which side the little spring goes on one of those diaphragms. I also go 5/16 on the float level by using a long shanked bolt.

There is some good carb info here: http://www.willysmjeeps.com/v2/modul...wtopic&t=11341

[Peter Phillips]

Originally Posted by Mike Kelly

I guess this is a original Carter ?

There is a guy on the G503 forum (scoutpilot)) who runs a business, he rebuilds these , he knows more than any of us will ever know. He will freely offer advice.

Is the throttle shaft worn ? A slight slop in the shaft and air will be sucked in. This air leak upsets the idle citcuits.

Also, a inlet manifold air leak ?

Have you seen this https://oldjeepcarbs.com/

Edit. Looks like a YS Carter was fitted. The old gaskets from a NOS kit will have shrunk , might not be sealing ?

Hi Mike,
Original YS carb
Throttle shaft is tight...in fact while I had it running I sprayed carb cleaner around every gasket mating surface and the shaft to hear a change in engine rpm, nothing I could tell.

The new base gasket was definitely garbage and leaked. I used the old thicker gasket with success.

I will look into those references you mentioned, thanks!

[Peter Phillips]

Originally Posted by rob love

A common problem I run into on the Jeep carbs is that, with todays ethanol poisoned fuel, those two little diaphragms on the front and rear of the carb will crack or puncture and you will not get a good running engine. Usually though, that is more of a flooding situation. I have had better luck with the ethanol resistant kits from places like midwest military, but even better is to stay away from the ethanol fuel as much as possible.

Note there are also conflicting illustrations in the manual on which side the little spring goes on one of those diaphragms. I also go 5/16 on the float level by using a long shanked bolt.

There is some good carb info here: http://www.willysmjeeps.com/v2/modul...wtopic&t=11341

Hi Rob,
I thought about the ethanol attacking old components but figured in the short term this thing should go for the summer at least until I get a newer one ordered....could be wrong here, lol. I'm thinking a newer kit is in the making and I'll definitely try the new float height at 5/16".
I'll look into the WillysM Jeep link, thanks!

As an added conundrum, I took another YS carb and gave it a thorough cleaning and adjusted the float and the jeep runs the same way which I found ironic. Could a fuel pump ever be able to overpressure past a needle and seat?
BTW, great to bump into you again at the Calgary Gun Show

[rob love]

A fuel pump is way more likely to produce less to no pressure than too much. They regulate by the spring under the diaphragm. Springs get weaker, not stronger.
A common problem, even in service, was the very fine particles of rust from the tank would make it through the course in tank filter, and either unsent the checkvalves in the pump or lodge in the float valve, causing flooding. The solution is to install an online filter, either before the pump or at the carb. The telltale sign this is the problem will be a very fine reddish sediment in the bottom of the float bowl.

If you used an original gasket kit, and the rubber was not happy with the ethanol, the bad results can occur quickly. Overall, they are a simple carb with little that can go wrong aside from those two diaphragm.

The calgary show is a great place to meet the guys from out that way. Only problem is there are way too many buyers vying for my time which cuts into the visitation time.