M38 idle

jerry72 · Posted: Sat Dec 10, 2011 10:38 am Post subject: M38 idle

Having trouble with the idle when engine is hot. Just installed rebuilt fuel pump so that wasn't the problem. Replaced both carter ys dia. with new ones able to tolerate the ethanol in fuel. That wasn't it either. New fuel filter. Mixture adjustment, still having idle problems. Any ideas???

Jerry

wesk · Posted: Sat Dec 10, 2011 10:55 am Post subject:

It helps to also describe the idle problem. Lopes, surges, uneven, dies off. misses and etc. Also a little background is always helpful. Just rebuilt the carb, was running fine until today, has set for a long time and etc.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

jerry72 · Posted: Sat Dec 10, 2011 11:32 am Post subject:

Surges, uneven, dies off. I've had the idle problem for a long time. Thought it was the dia. in the carbt.the problem went away for a short time then came back. Next had the fuel pump rebulit by then & now, (The dia. were cracked and fuel was getting into the oil), works fine however still have the idle problem when motor is hot. The engine does not miss or backfire just dies when in idle. Example I'll be coasting to a traffic light and the engine dies without any warning. I read somewhere (don't remember where) that this could be caused by the different materials between the carb. and manifold. Has to do with warping of different metals causing vacuum leak. Has anyone had this warping trouble??

Jerry

wesk · Posted: Sat Dec 10, 2011 2:38 pm Post subject:

No warping in this jeep.

There can be several explanations for the problem.

1-Fuel pedal linkage is changing with motion and at times letting the engine idle way to low so it quits.

2-Idle mixture adjusted way to lean.

3-Heat riser stuck open.

4-Throttle shaft worn excessively.

5-Vapor lock.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

jerry72 · Posted: Sat Dec 10, 2011 3:33 pm Post subject:

Thank you Wesk, I'll check all the items you mentioned.

Jerry

wesk · Posted: Sat Dec 10, 2011 4:08 pm Post subject:

On the vapor lock issue the Army published a bulletin for the M38 rerouting the line between the carb and the fuel pump further from the exhaust manifold.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

Cacti_Ken · Posted: Mon Dec 12, 2011 11:47 pm Post subject:

You might take out the idle mixture screw and inspect it for wear.
And the reason I say this is because my so call rebuilt YS had a worn out screw in it. Of coarse I couldn't get it to idle right and it ran rich.
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Tropical Veteran
35th Inf. Reg. "CACTI" 4th I.D. VN
Amateur Radio K5XOM

AeroE · Member Joined: Aug 31, 2008 Posts: 49 Location: SE MN

Is the re-routing bulletin available?

wesk · Posted: Wed Dec 14, 2011 1:21 pm Post subject:

The TB 9-804-6 supplemented the first M38 Operator's Manual TM 9-804 published in 1950.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

skyjeep50 · Member Joined: Feb 20, 2007 Posts: 606 Location: Illinois

Coil that's starting to fail?? Getting hot at slow temps when less air is moving through the engine compartment. My M38A1 had those symptoms until I changed the coil.
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1951 M38

Cacti_Ken · Posted: Wed Dec 14, 2011 10:32 pm Post subject:

When I tubed my pump outlet line, I turned the fitting 90 degrees horizontal from the position shown in the picture in order to get the line away from the motor and manifold. Straight toward the fender then bend upward to fit to the carburetor fitting. I Have done a lot of hot weather driving with no problems.
_________________
Tropical Veteran
35th Inf. Reg. "CACTI" 4th I.D. VN
Amateur Radio K5XOM

jerry72 · Posted: Fri Dec 16, 2011 11:03 am Post subject:

Found the problem or I should say problems.
Heat riser was in the open possition. Embarassed

after closing it the engine idled much better until I went out for a test drive. It started to miss again but not as bad as it had been doing, so I looked into the vapor lock trouble. I insulated my fuel line with aluminum foil just to see if this was the cause or did I have something else to worry about. With the insulation in place the engine ran great, no idle trouble so as you can see it was a combination of problems. Now that I confirmed the vapor lock issure, I will reroute the fuel line.
Thank you guys for your help and expertise.

Jerry

jerry72 · Posted: Fri Dec 16, 2011 6:34 pm Post subject:

ok now I'm confused. I recently had my fuel pump rebuilt by then & now and I noticed on the post above(tb 804-6) the output fuel line to the carb. on mine that has become the input line from the tank. When I received the pump I installed the fuel lines as is correct on this outline tb 804-6 however the pump would not pump fuel. I inverted the lines and it pumped. Is this reversal of input/output normal or has then & now assembled it wrong??

Jerry

Cacti_Ken · Posted: Fri Dec 16, 2011 6:51 pm Post subject:

Normally the suction port on the pump where you would connect the line from the fuel tank should be on the upper left side like the picture shows.
_________________
Tropical Veteran
35th Inf. Reg. "CACTI" 4th I.D. VN
Amateur Radio K5XOM

jerry72 · Posted: Sat Dec 17, 2011 7:00 am Post subject:

Ok then why has mine changed from the left to right???
My pump is the same as in the picture and is the exact pump I sent to then and now. Can pumps be wrongly assembled to change the suction to output????


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