carb swap - now engine shakes slightly at idle, etc.

[enferno]

early style 302, c4, rpm air gap intake, holley 4160

i had a 4160 double pumper on the engine, but 2 of the bolts in the metering block were stripped and started leaking. i got another 4160, but with vac secondaries, rebuilt it and popped it on. it idles and runs fine, got the idle mixture set properly with a vacuum gauge, however there are 2 things i'm noticing.

at idle, the engine shakes more than the double pumper did.

also, in park/neutral, if i rev the engine, the rpms will dip below where it idles (idles at ~1000, dips to 700 or so), then comes back up to ~1000. also, when driving, the engine seems to slow down in rpm a lot slower than the old double pumper. what might cause this? is this even an issue, or normal behavior for a vacuum secondary?

thanks!

 

[bacfire]

Sounds like you may have a vacuum leak in the new carb. Could be a worn throttle shaft, a warped metering block or baseplate, or possibly even a porous casting somewhere...usually a metering block. Or maybe (hopefully) you damaged a vacuum line elsewhere during the swap. Does the idle speed change much when you adjust the mixture screws? Try spraying a little carb cleaner around the baseplate and throttle shafts and see if the idle changes or smooths out. If so, you found a leak.