I just installed an 800 CFM carb on my 350. I drilled out the bypass in the baseplate, and the body, as well as drilled out the idle needle seats both a little larger than stock. I also trimmed the power piston spring. The motor is 10:1 Hyperutectics / TA intake. The specs on this cam are 488 / 502 230/238 @50 on 110 degrees, so its pretty lopey. It has all kinds of power in the upper band, and loves this 800 CFM carb with the 75 jets. The problem I am having is I cannot get the idle mixture right. No matter where I am setting this thing it doens't seem to have the fuel I need for an idle. However, the exhaust is very rich, but if I lean it out, it stalls. Am I missing something? I am tempted to go to a holley, but I have always gotten good performance out of the q-jets, and would like to stay with it. Thanks guys. -Jon
This is one of the biggest problems with the q-j carb. The idle circuit is just in adequate for any much over a stock cam. If you can start to close the choke and the idle gets better, you know it is too lean on the idle. The carb needs some re-wrk in the idle circuitry, you may want to contact some of the q-j specialists to wring this thing out. Jim Burek P.A.E. ENTERPRISES
Found a great web page to do this!!! I did some research on how to modify the carb, and I found this web page. If you have this same problem, and your not the type to pay someone else for the work(cheap like me.. )follow these steps, and it will be night and day! Thanks for your advice Jim! I will paste the link below, it was very helpful to me, and solved my problem. Thanks, -Jon http://personal.clt.bellsouth.net/clt/m/g/mgervin/garage/qjetidle.htm
Jon one of the things I personnally discovered wile ruining uh modifying the 800 qj is that most of the times opening up or using at all the idle air bypass ports results in a too lean condition thru out the opperating range. I block with lead shot(fishing weights) the holes cast into the main body aswell as the baseplate itself then i drill holes in the leading half of the primary throttle pltes starting at 3/32nds and going larger from there. The carb on my 350 right now that has a little smaller cam than yours at 224/235 and I had to enlarge the primary hole to .140 to get some adjustability back without having to crank the idle speed screw way up. You only want a very small amount of transfer slot showing and this one small modification helps in that area. You apparently already have the Roe rochester carb book judging from youre previous posts.
