Low vacuum
 

After a center carb rebuild, I am only getting 8" of vacuum from the fitting that is on the carb base. The carb does have the hot idle compensater. Only change I made was I switched from the base gasket with open center to the one with the 2 holes. Would this gasket change cause this problem? 65 setup, Thanks

Easy enough to check. Just install the original type gasket.

Small base 2 GC w/HIC may use this throttle body gasket.

I might of Mis-spoke, I changed the gasket between carb base and manifold

Open or 2 hole flange gasket will not affect the vacuum signal.

Thanks for the info

Did you have good vacuum before the carb rebuild? If so, there is likely something plugged in the idle circuit, probably the venturi cluster. Idle tubes, idle bypass restrictors, are the ones with small holes that could be plugged. If you give us the parameters of the engine--cam, C.R., cubic inches, etc., we can tell you what the idle circuit orifice sizes need to be. A moot point if it ran OK before the rebuild. PM if you need to.

Also, I've had low vacuum with a carb-to-manifold gasket with holes in it outside the two throttle bores. The base of the carb will not seal to the manifold with the "Chev" style gasket. You need to use a solid base gasket with only throttle bore holes and carb mount holes. As Kenth pointed out, the open or closed gasket makes no difference.

OP: Sorry to hijack your post.

Hello Dick,
Is the 66 center carb gasket the same requirement; with just venturi and post holes? I suffer from low vacuum for the front disk brakes and this maybe the cause. I run the tripower with a 455 with a big thumper cam. .560 lift.

Thanks
Joe

Has the center carb been calibrated for your cam? Let us know your engine parameters and we’ll tell you how to modify your center carb for decent idle, which equates to higher vacuum.

Hello Dick,
I've been away from the site for awhile and just picking up your message. Thank you for your offer. I'd like to take a raincheck as I'm working on putting her all back together with trim and badges from a new paint job. Then new tires and rims. Then I can concentrate on the tripower.

Once again I appreciate the offer on guidance. Joe