This may be simple to some, but, I'm struggling with some tuning issues on my 64 C10 with a 292, and a Rochester monojet. Under heavy tip in (romping on it) it, it backfires through the carb. I'm guessing this is a timing issue, and have done some work on the distributor. A general tuneup all around, etc. The vacuum advance can is new, and all the advance system cycles freely. I also had the Rochester Monojet gone though by a local well respected carb guy. After purchasing a vacuum gauge the other day to fine tune the air/idle mixture, I decided to check what kind of vacuum I was getting to the vacuum advance on the distributor. I'm not getting ANY. I'm getting 21" of manifold vacuum from the manifold, but, NONE from the carb. I am assuming that this is all hooked up factory, as the carb has a hard steel line with a collet threaded into it next to the air/idle adjustment screw that runs down to the vacuum advance with a short rubber line, but, when I check at the distributor end of that line with my gauge, I get no vacuum reading. Even up over 3,000 rpm. I can understand nothing at idle, but, thought I would get something once I ran up in the RPMs. I can unhook the steel line at the carb, and move the vacuum advance drawing in with my lungs, so, I know the line isn't blocked internally. A lack of advance would explain a backfire at tip in. Is this the correct location for the vacuum advance to be hooked too, or do I need direct manifold vacuum? Sure wouldn't think so, and it's not like there's a ton of locations to get vacuum from. I'd think that carb would be providing ported vacuum as the vacuum port on the carb is just above the butterfly, anyone have any ideas why it wouldn't be?
The Jalopy Journal
