The Stovebolt Site Forums The Shop Area Engine Shop Back pressure problem

I’ve got a 47 Chevy panel. Just did a valve job and cannot get the exhaust manifold to line up with the exhaust flange. Therefore there’s a big leak there. I’m going to have to take it to a muffler shop to get this fixed but in the meantime I need to move it. It starts but will only run at full choke. Take choke even halfway off and dies immediately. My question is does this lack of back pressure cause it to only run at full choke? Thanks for any help! David

Sounds like you have a leak at the intake manifold. Did you replace the alignment sleeves on the intake? Are they seated in the intake and head right? Did you take the intake and exhaust apart? If you did separate them, when you re assemble them leave them loose till the are secured to the head then tighten them.

Sounds like you have a leak at the intake manifold. Did you replace the alignment sleeves on the intake? Are they seated in the intake and head right? Did you take the intake and exhaust apart? If you did separate them, when you re assemble them leave them loose till the are secured to the head then tighten them.

The alignment sleeves as Tommy states are definitely critical and can be a REAL pain at times. It is absolutely important to wire brush the rings and the head / intake manifold then grease. Wiggle, wiggle and don't cuss. Doc

"lack of back pressure": mythical problem

Yes I used the original alignment sleeves and made sure they were in. Is there a particular position they should be in; like All the splits all needing to be In same position?

All the sleeves do is position the manifold in relation to the head. They don't seal vacuum- - - -that's what the gasket is for. If you're talking about the head pipe between the exhaust manifold and the muffler not sealing, it has NOTHING to do with how the engine runs. Find and fix the vacuum leak you created during assembly, and it will run properly with or without the exhaust system connected. I use an unlit Propane torch moved around all the mating surfaces between the carburetor, intake manifold, and head to find vacuum leaks. The engine will speed up or smooth out when the gas gets sucked into the leak. Acetylene works for leak testing, also.
Jerry

Thanks much for that tip Jerry. I will try the propane torch procedure. I’m also wondering if something might have stuck in the carb, as I had the carb and manifold assembly bungeed off to the side and it was laying on it’s side.