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I got my m38 out from winter storage. The changes I have made since last summer is a new carb from midwest, and a re-rebuilt fuel pump. The jeep starts just fine, but will not idle with the choke off, it is about 1/4 to 1/2 on. I have disconnected and plug the vacume system to see if I had a vacume leak there with no change. Anybody had any ideas on what I need to check next?

-Bill

Hello Bill;

I had a problem similar to my M38. in mine case that the problem were gasoline lack, after changing 2 times of fuel pump without success than I finished identifying that the problem was in the rod of the fuel pump that did not make the course enough to pump the gasoline for the carburetor. To decide this problem I had that to increase the thickness of the rod of fuel pump.
I hope that you understand my explanation.

Best Regards;
Ederson from Brazil.

Make sure you don't have a vacuum leak under the carb at the base gasket. They are famous for this. I had to make paper gaskets for both sides of the block and put star washers under the nuts or they would loosen. If that doesn't help, do a check by spraying a little carb clean into the carb while running and see if it picks up the dead spot. If it does, your new carb isn't delivering fuel through the idle circuit. Mine had a small fuel hole plugged brand new. New doesn't always mean it is ready to go. A small passage could be plugged or blocked. Don't get carb clean on new painted surfaces or it can wreck the paint! I sprayed the carb clean into the inlet tube between the air cleaner and the carb. It ran so nice until I stopped spraying. John

I will check that and report back thanks for the carb cleaner idea.

You can also go the propane enrichment method. Using a bottle of propane gas release a slight flow of raw propane gas near joints and gaskets in the induction system and any increase in RPM or smoothness means that spot has a vacuum leak.

Even though it's a fresh carb and pump did you physically inspect the interior of the carb (all passageways), the carb float level setting, the correct springs on each side for the diaphragms and their correct orientation, make sure you have the correct part number metering rod, check fuel pump output pressure with an accurate gage and did you use the correct fuel pump to block spacer?

The block spacer is correct. It is the same pump I was running last year, Just the vacume side was not working, so I took it apart and now the vacume side works fine. I will have to test the fuel pressure. I am leaning towards the carb base gasket right now but will try some other things first, such as the propane trick. I will also get a fuel pressure test done when I find the right tool to do so. For the heck of it I did a compression check and every cylinder is pretty even with number one being the lowest at 105, with all the others around 108

Ok I took the carb off to send in for repair, when I got the carb off the base gasket crumbled into about 3 parts. I called John up and before I send the carb in he is going to send me a new gasket. If that fixes it I am good to go.

ok still having problems. I sent the carb back to get checked out. I got the carb back and put it on. Now it will idle better but still not great. It has plenty of power. If I come to a stop sign the engine will have a real high idle and then slowly come down to almost stalling. The jeep however only stalled once on me tonight, and that is just as I was pulling in to park it. I opened the hood and I could her a strange sucking sound coming from the back of the block, the engine was not running at this time. Any ideas? I am going to put a vacuum gauge on it this weekend, any one have a chart to make sure I am reading the gauge correctly?

Problem is all fixed. John sent me another carb. Thanks John for the great customer service and helping me track down this problem