M38 engine loping, need help

[MajBen]

Hi Guys, I know this question has been addressed numberous times, but I am posting it again seeking fresh suggestions. I have a different situation than one who is just trying for the first time to start and adjust a recent overhaul---somehing has gone wrong after running correctly.

During the past 6 months, I have started Leatherneck numberous times in the shop. The engine from the beginning purred and sounded great. Recently on a trial run for about 10 miles, she drove and ran great. But, at the last mile, the engine started loping. Now, in the shop, the engine runs at about 1000 rpm but won't idle and is extremely rough.

During restoration, everything about the engine was either replaced new or rebuilt. It acts to me somewhat as if it has a vacuum leak although, from my limited experience, it is far too rough. Yesterday, I checked all vacuum lines and fuel line connections. It does not act to me like it is a timing or point problem.

I really think it is a fuel/vacuum problem combination. Both fuel pump and carb were overhauled by professinals---I have never personally worked on either before. I have a feeling that it is something that would be very obvious to many of you.

Your suggestions by prioriity will be greatly appreciated. Semper Fi Ben
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Semper Fi Ben

[wesk]

Ben,
Probably fuel delivery issue. Do the simple things first.

Check for loose manifold and carb parts.

Run it with the tank cap removed.

Check fuel delivery pressure.

Blow the line clear back thru the tank.

Check and record vacuum readings with engine running.
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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

[MajBen]

Hi Wes, thanks for the come back. These are good suggestiions and will do as I want to do all the obvious before I have to get serious. SF Ben