I blew one on this carb!! It is why I had someone else rebuild it! Of course, the NASCAR 390 is a lot different from most of the other 390 Holleys.
It looks more like the old 850 double pumper. It is all mechanical. No vacuum secondary. no choke. Not even a choke horn. No vacuum ports of any kind.
If you're dealing with one of those with the vacuum secondary, you can change the spring in the secondary servo/dashpot to open faster or slower to tune the stumble or bog, or to bring the secondary in faster. I've also seen the vacuum passage drilled or bushed to increase or decrease the vacuum signal.
Last edited by Blackwater; 03/06/1706:58 PM.
Never use a minor caliber bullet on a major caliber adversary
