Posted: Mon Feb 22, 2010 5:42 pm Post subject: Plugs Fouling
Ok, I am having a problem with plug fouling. Dry carbon fouling is what I think it is called. A lead up to this is, m38a1 was running a little rough, and not a great spark. Replaced coil, condenser and points, rotor and cap, as well as 4 new plugs. Also, rebuilt the carb and cleaned 40 years worth of gunk out of it. It was def. running rich before, but it seems good now, ie. no black smoke. I also dry tested the compression and it was good, about 120 across the board.
I drove the jeep for about 20 mins, and let it idle for about 5 mins, and at that point it started to miss and sputter again. Took out the plugs, they were black and sooty. Cleaned the plugs and it purred like a kitten again. The air fuel screw it turned right in and blacked off a half turn.
Joined: Feb 18, 2008 Posts: 113 Location: Wauchula, Florida
Posted: Mon Feb 22, 2010 9:26 pm Post subject:
I had kind of similar problems with my M38 recently. I had a newly rebuilt Carb and everthing was running great then my problems started. Running rich, fouled plugs and so on after going over everthing imaginable I came back to the carb and found that the diaphragms were bad and after only 6 months and 5 - 10 gal of gas BUT sure enough they were BAD!!!
The carb rebuild kit I used was purchased from Debellas and is considered the minor overhaul kit.
The diaphragms were grey in color.
I live in Florida were the gas is mixed with less than 10% ethanol as advetised.
I purchased a new master overhaul kit from Midwest Military.
These diaphragms were red in color.
After rebuilding it again it is now running great like before.
I also changed it diet and found some non ethanol 87 octane gas and mixed it with 100LL avgas ( 4 gal of 87 to 1 gal of 100LL ) and it seems to like what I've done.
AH HA! CHeck the little things first.... The bolt at the back of the carb next to the valve cover had worked a little loose and was letting air in. Tightened up, reset the float again, and purrs like a kitten.
Last edited by mcafee on Tue Feb 23, 2010 1:03 pm; edited 1 time in total
Joined: Feb 20, 2007 Posts: 606 Location: Illinois
Posted: Tue Feb 23, 2010 1:02 pm Post subject:
As you noted you may have some other problems not related to the spark plugs but if the fouling continues you may also want to check if you have the right plugs for a M38A1 - 2245's and that the thermostat is working properly. If you don't have a thermostat installed or a 165 degree thermo, that can prevent the engine from warming to it's normal operating temp which can lead to plug fouling. A 180 degree thermo will help. Good luck! _________________ 1951 M38
Loose carb base bolt allowing air to leak in results in a lean mixture which does not leave soot on plugs. The lean mixture burns very clean and hot leaving the plugs a grayish white.
A plug that is truly fouled (shorted out) will miss or not fire at all.
It is quite common to get a soot covering on plugs when the jeep is operated only a short time or distance and wasn't given enough time to warm up to normal operating temp. If you drive the jeep at least 30 minutes with a thermostat installed and working and timing set correctly then shut it down immediately (not allowing it to idle) the plugs should be clean and dry. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Sep 14, 2006 Posts: 20 Location: Maumelle, AR
Posted: Mon Mar 08, 2010 8:47 pm Post subject:
I bought a new set of plugs few years back. The prices have gone up a bit but aren't as bad as some people were reporting (upwards of $18 each). Here are the links depending on which ones you need/want.
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