Stuttering

MajBen · Post by **MajBen** » Sat Jul 03, 2010 2:18 pm

Hi All, it's been awile since I posted. With a very few exceptions, I finished restoring my M38 51 in late 2007 or 08; it has been setting evry since due to health problems. My son and I are nearly sure we are going to put it up for sale as he does not have time for it and I can no longer be involved due to health problems.

We started it this morning after nearly a year and it ran and purred like a tom car over thick cream and then it began to stutter or cut out when it got to temperature. If you are near the accelerator an pump it it will come right out of it but if not, it will usually die. It is definitely a heat related problem and it has been with me since I had to quit. I have posted this probem before but never had time to follow through so if anyone has some suggestins, I would appreciate you posting them. As those of you know who helped me so much during my restoration, except for the USMC green paint it is almost factory with so many new parts and lots of NOS at that. So, I need to do something with it, but sure would like to get the stutter out first. Thanks and Semper Fi Ben

Post by **wesk** » Sat Jul 03, 2010 7:26 pm

Hello Ben,
First place to look would be the heat riser. Is it stuck in the heat position. This will get the manifold at the base of the carb very hot and at idle it will get too rich and stumble and die unless you rescue it by popping the throttle open and getting more air in.

Wiltshireboy · Post by **Wiltshireboy** » Mon Jul 05, 2010 11:30 am

Hi Wes, I have a problem similar to this with my M38A1, (but i can drive (towing a trailer) for about 12 miles and then she splutters a lot and i can keep it going by reving it but she really struggles and eventually stops and I have to wait 20 to 30 mins before she starts again), so am interested that the heat riser may be set in the heat position. Thing is I dont know where the heat riser is or if I have one. Andy

53a1 · Post by **53a1** » Mon Jul 05, 2010 12:37 pm

No heat riser on the A1. Mine would sputter before I got the thermostat situation under control. It would happen around 220-230 degrees then I would shut it down. Probably vapor lock.

Wiltshireboy · Post by **Wiltshireboy** » Tue Jul 06, 2010 2:22 am

many thanks, i am going to have a look at it tonight, the engine temp doesnt seem to be going that high though (around 160 -180). andy

Post by **wesk** » Tue Jul 06, 2010 10:05 am

When the engine runs fine for a short while and then starts to act like it is short on fuel I would first suspect a plugged tank vent system. Remember your tank is vented at the top adjacent to the pickup line and through the cap. So the easy troubleshoot way is just remove the cap and drive it. If problem goes away either the cap vent is bad or you have a selectable cap and someone has selected the fording position on the cap, or the tank's vent fitting and/or lines is plugged. Early M38A1 had the vent from the top of the tank plumbed to the air cleaner so it can be plugged at the tank or along the line to the air cleaner. Later M38A1's just had a little hooded vent valve on top of the tank.

This is the late A1 plumbing system. Note the small vent valve that screws into the vent housing on the tank.

Here's the inside of the selectable fuel cap vent.

Another note of caution, when the ignition coil gets hot if it is a weak one it will start to cause some of the symptoms you are experiencing. If restricted fuel venting is not your issue then you will have to ohm the coil both while it's hot and cold.

This illustrates the testing of your coil. Make sure the two wires are disconnected before using your ohm meter and make sure your ohm meter is either aut-ranging or that you select the correct range.

Wiltshireboy · Post by **Wiltshireboy** » Wed Jul 07, 2010 2:46 am

Thanks for this info Wes, I drove the jeep last night till it failed and we found there was a weak spark. this improved as we waited for it to cool. i had already checked the venting of the tank which is of the early type you describe and it was clear. I will now check the coil ohms, hot and cold, later today. many thanks. Andy

Wiltshireboy · Post by **Wiltshireboy** » Fri Jul 09, 2010 2:16 am

My readings on the coil were: Cold: 5.9 ohms and 9.63 K Ohms. Hot but not stopping the engine: 7.5 Ohms and 12.15 K Ohms.
Does this mean the coil is on the way out? or do i need to re do the hot readings when the engine fails? andy

Post by **wesk** » Fri Jul 09, 2010 8:32 pm

Are both vent lines properly plumbed and connected to the distributor?

Wiltshireboy · Post by **Wiltshireboy** » Sat Jul 10, 2010 2:04 am

Thanks Wes. Plumbed fine and clear. Good suction on the pipe on pump side of distributer, not very much suction on the air intake side. lines seem clear. Possible block inside the distributer that I will look at later today. Are these vents simply to cool the coil? andy

Wiltshireboy · Post by **Wiltshireboy** » Sat Jul 10, 2010 3:04 pm

I have now checked inside the distributor. I little oil like liquid at the bottom on the coil and in the casing. have cleaned this and put it back. there were no blockages on the vents. I will driven the jeep today for 14 miles with no problems but guess the real test is with the trailer on the back. Thanks for all your help. Andy

Post by **wesk** » Sat Jul 10, 2010 10:21 pm

Oily substance can be one of three. From the engine side oil. From an overfilled oil bath air cleaner. From a leaking coil.

Primary purpose of the vent line is to remove ionized air from the distributor housing. Secondary purpose is to help cool the distributor coil when outside air temps are high.