Taller Intake Manifold Question

[Paul Schooley]

I changed out my stock intake manifolds (one was broken at the mounting holes to the engine) with taller ones (1 inch taller) that say REM on them. I 'think' they're PMO's but not sure. Regardless, I've noticed on the shakedown run that when I get on the throttle it's great but if I take my foot off the loud pedal the engine will die. I was under the belief that I wouldn't have to rejet the carbs for a taller intake manifold. Is this right? Or should I be looking for something else to be the culprit. It also runs kinda crappy at low rpms. Any advice is appreciated.

[Steve@Rennsport]

My best advice would be to look for a vacuum leak or two between the manifolds and carbs and/or manifolds and heads.

[ljowdy]

The best method for finding vacuum leaks is via a can of carburetor cleaner. Spray at every connection (ie, manifold to head, carb to manifold, hoses, etc.

I used to use ether and try to detect an increase in RPM's but found that carb cleaner causes the engine to stumble and is easier to detect..

[Paul Schooley]

Carb cleaner sounds good. My buddy suggests a small propane torch (without the flame obviously). That should raise the rpms a bit if the propane gets sucked in to a leak. I'll try both. First I'm going to remove the air cleaner assy. and recheck tightness at all mounting points. I used all new gaskets and checked tightness 4 times before firing up the engine the first time. I'd like to use a torque wrench but it's difficult to use in some of those locations. Anyone know the torque specs for the carb/manifold and manifold/engine mounting points? Webers on top.

[ljowdy]

I've also experimented with propane and as I said above, ether.. It's easier to detect a stumble in the idle with the carb cleaner than it is to detect a small increase in RPM's using propane or ether