M151A2 won’t stay “lit”

[Crux444]

I just replaced the exhaust and intake manifold gaskets on my M151A2 - great, no more “farty” exhaust leak from under the hood. Upon doing a start check, the jeep that used to run like a top now doesn’t seem to want to stay lit. I have to keep the choke open at least 1/4” and throttle on as it stalls out at low idle.

I have checked all of the connections and they are tight, and there’s no parts left in the shop cart. What gives? (And don’t say it’s because infantry officers shouldn’t play in the first line combat service support sphere!).

Any insights are welcomed.

Thanks,
Sean

[Rickf]

I will bet you have a large vacuum leak at the intake manifold. It is being held out away from the head and gasket by the exhaust gaskets. Get it running and pull the hand throttle out to the point where it will stay running. Now take some carb cleaner and spray around the intake manifold where it meets the head. Be sure to get underneath of it also and be sure the hose from the car to air cleaner is on. If the engine changes at all during this test you have found a vacuum leak. Did you follow the torque specs in the manual to the letter? The light duty head and heavy duty head have different specs. Basically the A1 never used gaskets for the exhaust so when used you have to use double intake gaskets. This is not usually a problem with the A2 but if the upper bolts are tightened to tight they will crush the thin exhaust manifold and rock the intake on an angle to the head and you have a leak. If this is what happened you will also need a new exhaust manifold.

[muttguru]

I just replaced the exhaust and intake manifold gaskets....Sean

Sean,
please describe the ehaust manifold gasket(s) that you replaced. Are they the square fiber type with the tags that bend into the manifold?

And here are some supplementary questions:-
1. Did you check the exhaust manifold openings for deformities / crushed edges using a steel ruler edge?
2. Did you use a new exhaust manifold or re-use the old one?
3. Did you use the complete exhaust manifold kit?
4. Did the kit contain the instruction sheet for installation?
5. Did you use a torque wrench to tighten the bolts?
6. Did you tighten the bolts in the correct sequence?
7. What torque settings did you use for the bolts?

Ken

[Crux444]

Ken, I didn’t check the exhaust manifold for deformity, but I did use the complete gasket set (the one with the fold in tabs for the exhaust manifold), and I replaced the intake manifold gaskets, the one on the carb, and the exhaust pipe.

What I did NOT do was use the proper torque settings in the stated sequence (DUH!), so have ordered another gasket set and will do it properly now that I have a torque wrench so I don’t just use the handrailic guesstimation method.

It’s only $$$, right? Note to others: don’t be a dumb-@ss like me…

[Rickf]

Did you do the vacuum leak test before you take it all apart to make sure this is actually the problem? And I will add on hint, if you get a kit with new stainless steel bolts throw those bolts in the trash and go to a Tractor supply store and get grade 5 anodized steel bolts the same size. You will never again have to worry about broken bolts removal from the manifold. Whatever wizard thought of using stainless bolts in cast iron was a moron! The stainless steel bolts are soft so the threads gall as they go in and you end up with reverse fishhooks on the threads. The harder you try to remove them the harder the bite in. And penetrant just makes it worse because they are not rust seized and lubricant would be much better than solvent.