M38A1 Ignition system question

Casey B · #1 23-09-11, 08:22

Need to know what you think. I last ran the jeep about 2-3 weeks ago with filthy fuel in the old fuel tank and since then have changed out that tank for a clean one. When it ran before it was slightly rich but no missing or really rich smell. I ran it today with new fuel and the new tank and it started really well and was on choke then when I let the choke off and it was warm it still ran rough missing and sputtering. I checked the plugs and the first was fuel soaked so not sparking the next black with soot, so too rich.

Any thoughts on why it ran well...better with the crappy fuel and dirty tank and now it is not?

I was thinking that it may have been set to run rich as the feul was old and probably the pick up was slightly clogged with rust?

Any ideas on where to get a decent price on spark plugs for this as well?
M38 A1 1953/ford built engine..Hurricane

I will try to regap the worn plugs to see if this helps first.
Fuel mixture adjust is on Pas. side of carb correct?
No manual yet so working blind here but getting there.

Thanks for any suggestions and Info!

So close yet so far...

Hanno Spoelstra · #2 23-09-11, 09:34

Casey,

Please use a more specific thread title in the future. I changed it for you this time. This is primarily a CMP forum, other vehicle types are welcome too, but please be more specific so the readers know what the question is about.

Thanks for your consideration.

Regards,
Hanno
MLU Administrator

rob love · #3 23-09-11, 14:32

Any rust particles moving through the fuel system will cause the engine to flood. If you lift off the top of the carb, and find what looks like miniscule particles of red sand, then the rust is your culprit. The needle valve will not tolerate these pieces. Install an inline fuel filter before the carb, and even a second one before the pump. I have seen instances where the sediment from the tank will even case the seats in the fuel pump valves to remain open.

There is a course filter inside the fuel tank, but it is not enough to prevent this type failure.

Casey B · #4 23-09-11, 16:15

Thanks Rob I'll do just that..and some new plugs couldn't hurt...This problem isn't just an M38A1 problem then eh...?LOL

Comox Air Force Museum · #5 23-09-11, 18:27

Casey, you might also want to check your distributor cap. M38A1's are notorious for cracking if the screws are overtightened holding the inner bakelite cap in. That might explain the wet plug.
Rob

SteveJ · #6 24-09-11, 05:16

Also you might want to check the ignition harness. Sometimes when they are unscrewed they bind up and twist off the wire.
Ive always run the resin filter in the tank of my M38 and have had no problems. but changing it or cleaning it as the TM describes would a good idea. The carb has only basic idle air adjust but the idle circuit is sensitive to contamination also a diaphragm may be perforated. If all else fails you might want to do a carb kid. Midwest military has a good one.

rob love · #7 24-09-11, 13:22

In your first post you asked about decent prices for the spark plugs. Depending where you buy them from they can be very expensive. One of the modern replacement numbers for the old plugs is Autolite 2243 for the old AR5S, and 2245 for the old AR7S. Rock auto lists both the 2243 and the 2245 for $6.63 each. That compares very favorably with the $15 plus that many dealers list them at.

The 2243 is the colder plug, the 2245 is hot. Engine condition along with type of usage would dictate which plug to use.

Casey B · #8 24-09-11, 19:14

Awsome advice ! thanks guys i have a sunny day all day to work on it and the wife is away at a course so freedom as well! thanks again. we'll seeLOL

Casey B · #9 25-09-11, 05:34

Took the carb apart yes lots of red dust rust dust that is but flushed the lines and put the in line filter in before the pum and it caugh a little rust not much ...so cleaned the carb and it all looked pretty good so took a chance and it fired right up and ran really well!...for about 2 mins LOL! Ordered a rebuild kit and some plugs for it. I figure there is a hole in the diapham and when it builds up pressure when you step on the gas that's it it floods out and runs rough and rich...so I wait a week while it wants to rain...?
Might have to get a top for it soon?