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I have had my M38 for 43 years and two years returned it to military. The fuel pump , carburetor and gas tank were rebuilt at that time. It is on page 4, bottom center right of the photo gallery. I was heading to a car show and it suddenly started to run rough and back fire. I pulled the choke out half way and it began to run fine. I continued to the show and back from the show to home with the choke half out, and it ran fine.
Since then I have replaced the fuel filter in the tank and the front carb diaframe but not the rear one. test driving it today it did the same thing again, so I loosened the gas cap, thanking the sealed system could be the problem. It did not Help. Has anyone else had this problem and what needs tobe fixed? Thanks Bob Major[/b]

Hello Bob,


Needing the choke to run means either:

1: Too much air.

Look for vacuum leaks with the carb base gasket, intake to block gaskets, intake cracks being the primary culprit. This is easiest done with propane enrichment method.

2: Not enough gas.

Check fuel supply all the way to the tank. This includes a Pressure and Flow rate check at the output of the fuel pump. Make sure there are no small leaks allowing air into the fuel plumbing between the pump and the in tank filter. (these will cause the pump output to be reduced because it can suck in air though the leak.) Make sure the in tank filter is not plugged, Inspect the filter stand pipe for rust holes causing the pump to suck air as the fuel level drops and exposes the holes.

Then move on to the carb float setting. metering rod installation and diaphragm. Then with the carb air horn up also check for evidence of any sediment in the bowl. If any is found remove the carb and clean all passageways out. I like to use a can of spray parts cleaner with the skinny straw and squirt it in each orifice and confirm I have flow at all outlets of the circuit.

Thanks Wes, I did replace the intank filter and stand pipe. The intake manifold was replaced when I put it back Military(Still could be Bad). The suddenness that this occured, bothers me. I belive the problem in the fuel delivery system. I checked the float and in carb screen, all looked ok. I will do the propane test when I have time this week and let you know the results. Thanks again Bob

You posting says you replaced the intake manifold...

I have a suggestion to try... start thejeep, spray the intake around the block with starter fluid... if the jeep idles up there is your problem... I had a vacumme leake real bad in that area...

I finally fixed it by taking both manifolds and the gasket that goes between them to a machine shop; I had them put them together and then machine the block faces as one... solved my problem...

The intake and exhust manifolds were not seating properly...

I installed a new manifold gasket and have not had a problem since...

Hope this helps...

Hal,

That's what is essentially done with a propane enrichment test. It's safer with the propane gas being sucked in and enrichening the mixture. Spraying wet starter fluid can result in an open fire if it hits anything really hot and can back flash to the can and blow the can up. With the propane bottle an accidental ignition will only flash back to the nozzle which is designed to allow a burn. .

Wes,

A person uses what he has available, I was taught to use starter fluid or some other spray can type of fluid... the point is to find the leak and get it fixed...

My symptoms prior to the repair were the same as described in the post...

Just making a suggestion...

I totally understood that. My point was simply the propane torch is safer. And this was offered to Bob as a better and safer choice and was not meant as a chastisement of you methods.