When I try to adjust the idle mixture screws on my Q-jet, the motor seems to run better when they bottom out, IE - all the way in.. If I turn them out more than a single turn, the idle degrades too. What would cause this? I am in the process of getting another Q-jet and am going to rebuild it as the one I have is for a 72 Buick 350 and it's sitting on a 71 455. I found one for a 73 455 that I plan on throwing a kit into. My problem is I'm also running a 200R4 and need the TV hookup on the carb and most Buick Q-jets are missing this special hookup, the 73 has the same as the one I have now, so it will be an easy swap. Thanks for any info on this idle issue. Keith
Haven't played with a 350 carb, but it may not have the idle air bypass curcuit. On a big motor without this, the throttle may have to be open too far at idle to get enough air to run the motor, thus bringing you out of the idle curcuit and into the transition curcuit.
That makes sense, thanks for the reply. Strange thing is, it actually runs fairly well like this. Idle is OK, no bogs or flat spots, starts excellent. I just hope the new carb runs as well once I get it swapped. Keith
You might want to check if your idle speed screw is turned in too far that it's cracking your primary throttle blades open.
When I had the stock 76 2bb I had the same problem when setting the screws. Mechanic tried it with a vacuum gauge and said there was carbon buildup in the carb. A shot of carb cleaner and some running it with the screws removed can clean it out. Then you put the screws back in and try again, it may not be your problem but it wouldn't hurt.
I'd be looking for plugged (or partially plugged) air bleeds into the idle circuit. At any rate, the idle is too rich. There's something wrong. You just need to find it and fix it.
