B&M 144 vacuum leak at the manifold

I have an old 144 blower on a 400 SBC. The blower is rebuilt and so is the engine. The engine was built specifically for that blower. It won't idle below 1000 rpm and when I put it in gear it stalls. The transmission is fine and it has a new B&M torque converter.
When it's running, if I spray carb cleaner at the point where the blower attaches to the manifold, the rpms jump about 300-400 rpm. Must be a vacuum leak. Mostly at the front and passenger side. I pulled the blower of and put a straight edge (several straight edges) on the manifold and found a high spot at the center, but it was less than .002". I took a stone to it anyway any removed the high spots.

I put it back together with a new gasket and there still appears to be a vacuum leak. Anyone have any suggestions? I torqued the bolts to 11 ft lbs, the instructions say 10-12 ft lbs.

thanks

It sounds to me like you're doing everything correctly. Have you tried applying any sort of sealant to either side of the intake gaskets to see if that helps seal off the leak? I know that's not normal practice, but it might be a way of solving your problem.

Are you certain the issue is a gasket leak? Maybe the blower housing has a hairline crack? It's a long-shot but it might be worth having the blower examined for cracks in the suspected area.

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Originally Posted by Madpickinskills

I have an old 144 blower on a 400 SBC. The blower is rebuilt and so is the engine. The engine was built specifically for that blower. It won't idle below 1000 rpm and when I put it in gear it stalls. The transmission is fine and it has a new B&M torque converter.
When it's running, if I spray carb cleaner at the point where the blower attaches to the manifold, the rpms jump about 300-400 rpm. Must be a vacuum leak. Mostly at the front and passenger side. I pulled the blower of and put a straight edge (several straight edges) on the manifold and found a high spot at the center, but it was less than .002". I took a stone to it anyway any removed the high spots.

I put it back together with a new gasket and there still appears to be a vacuum leak. Anyone have any suggestions? I torqued the bolts to 11 ft lbs, the instructions say 10-12 ft lbs.

thanks

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have the heads been milled, this will sometimes cause sealing issues.
what gaskets are you using? some gaskets are thicker and will compress more to seal up irregular differences in gaps
ie; if the angle of the head intake surface is not exactly at the angle of the blower intake surface... ::topsy_turvy:
for a sealant that could handle the boost also; look into pipefitters dope for sealing steampipes...