M38 help needed

[Schultzie]

Have a 52' M38 that is giving me fits and I am curious if anyone could possible help with this issue.

I can get the jeep started and it will idle well however, as it warms up and as you try to drive it will lose power, hesitate, pulse, backfire and want to stall. I had found a crack in the exhaust manifold with a leak so that has been replaced with a new manifold with the heat riser setup. Also have replaced the intake, new/rebuilt YS 637 carb, new dual action fuel pump, new fuel pickup and sender, new water pump, new distributor cap (was cracked) and new 24v coil, condenser, rotor and points and 24v plugs. Have had it to several places to fix, they have timed it but the problems continue. Any thoughts?

Could it be that the heat riser is not installed correctly?
Or the vent lines to the distributor needs replaced or blown out?
Or the brass bushing that the distributor shaft runs through worn and creating wobble at high speed and not contacting the points?
Could it be the new carb?

I am at a loss and need some expert advice as no one seems to be able to figure this out...anyone ever heard of such problems and what might the correct solution be? Thanks for looking and thanks for any insight given.

[mdainsd]

Welcome to the forum!

Scroll through this forum "Technical Knowledge Base", there are many threads on exactly this subject.

BTW, when you say new coil, it is chrome? These are suspect at best, and often exhibit this behavior.

Valve lash adjustment comes to mind when problems like this are temp related.

At any rate the threads I mentioned have many good suggestion to help you figure this out.

[wesk]

First and easiest to check is the fuel tank vent system. Drive it with the gas tank cap removed.

If the problem goes away fix the tank vent system or if you have the early cap with a selectable valve in it select the vented position.

Make sure both fording valves are in the open position.

Check the resistance on the coil, both primary and secondary, both cold & hot. A big change when hot in resistance will dictate a new coil.






The M38 uses this diffuser at the base of the carb. Many fpolks forget to replace it.


Intake fording valve in open position.


Crankcase fording valve in open position.


Ohm testing coil


These are the two different heat riser spring arrangements found most often on the L134 intake/exhaust manifolds.


Make sure the purple bowl vent line and ports are not plugged.