Cant get this thing to idle!!!

[71ConvtSkylark]

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

[buick535]

71ConvtSkylark said: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

[71ConvtSkylark]

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

[David Butts]

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.