I know very little about carburetors. The Q-jet I run is way too rich for my build, but I'm afraid to mess with the adjustments, because I don't want to lean out the mixture too much and burn up the engine. I bought a vacuum gauge, but I don't know which port to hook it up to, and I'm not sure what I'm doing. I bought the "How to rebuild and modify Rochester Quadrajat Carburetors" by SA design, but it doesn't say anything about adjusting them. That's kind of the reason I bought the book, so I could get my adjustments where they need to be. Any help is greatly appreciated. -Josh
Connect the vacuum gauge to any port that has vacuum at idle; tee it in if you have to so that whatever accessory it's supplying vacuum to is still functional. Adjust the idle mixture screws for highest vacuum; re-adjust curb idle speed; re-adjust both idle mixture screws for highest vacuum, re adjust curb idle speed--you get the idea. When the mixture screws have highest vacuum; and the idle speed is nearly perfect--turn the screws "lean" about 1/8--1/4 turn (each), just enough to reduce vacuum about 1/2 inch. Touch up the idle speed screw if needed. The final lean-drop will make a HUGE improvement in emissions while not making much difference at all in idle quality. Remove the vacuum gauge; install the air cleaner, shut the hood, open a beer.
Do your self a Favor and send the carb to John Osborn ,,He is the man , told him what i had and he built my Qjet , It is so responsive Very impressed Worth every cent of the $300 for the overhaul r,ebushing ,rejetting and mettering rods and what other Majic he does Awsome Dave
good start point for a stock Qjet is turned all the way in, then 1.5 turns out on both the idle mix screws. Should get you close to start.
Josh, Experimenting with idle mixture adjustments won't hurt the engine. Following Schurkey's advice is a great way to get the good idle and off-idle manners back if that's what you're trying to do. If you're working on primary and secondary mixture adjustments, those adjustments involve jets and metering rods. Before you go to that extent let us hear from you. Devon
