I just rebuilt my original 350-2 with a rochester 2-jet in a '71 skylark. It started up well, I broke it in, and it runs well, however, it has a big stumble off idle, which causes it to stall in gear when hitting the gas as you normally would. when you gas it about an inch at the throttle linkage, when it's warmed up and the choke is open, it stumbles out, the vaccum drops, tha\en it catches and revs up fine. if you gas it very slowly, it usually won't give this problem. It has most the symptoms of a air leak. I capped everything off, including the vaccum diaphrams which I found to leak, sprayed carb spray all around carb, intake and ports, no more leaks. and it idles fine. Ignition and dwell is at exact factory specs. I tried every fuel mixture from 1-4 turns out. I did rebuild the carburator, in a parts cleaner and blew out every port. the strange thing is, the problem does not occur when I manually close the choke to about an inch open, again making me suspect an air leak, but an increase fuel mixture will usually effect that when richening, and it does not. I rechecked the float, right on, and even messed with the accelerator pump by manually operating it, no change. I checked the plugs, no oil, so I don't think it's leaking from underneath. the only thing I have left is the fuel pump. it is running 5 psi pressure when hooked up directly to the guage and not the carb. when I hook it inline with the carb, it runs 4.5psi. I know that's a little out of spec, but figured it would still runn Ok since some cars have 4-7 psi as spec. I don't want to waste the money on a new carb if it's not the problem, and it is a numbers matching car with all the paperwork, so I really don't want to replace the carb. by the way, where can I get new choke vaccum diaphrams? any help would be greatly appreciated, no body seems to be able to help me with this, i have been stuck on this for over a week and I need to move on to the body. also, does anyone know what the cone shaped screw going into the back of the main body is for? I've seen many other 2-jets that do not have this, I 've tried adjusting this to, no results. thanks
The cone shaped screw...does it have vacuum fittings on it? If it does, then that is where you hook the PCV valve and another vacuum line coming out of the firewall up to the carb. RE: Choke vacuum diaphragm (choke pulloff) go here: www.carbsunlimited.com RE: Stumble... Check your timing and bump it up to 10*. If that it too much, then back it off until it's just enough. How old are your points?
the cone-shaped screw is above the pcv port, on the main body. it is like a jet that screws in beyond the outside surface of the body. it uses a small flat blade screwdriver to drive it in, and seems to go accross or into some vaccum port by looking at the bottom of the carb. I tried turning it all the way in and pulling it out a bunch, and I didn't notice any changes. 2.) I set the timing at 10* initial as specs call for, I also experimented with more advaced and more retard figures, and with and without the vaccum advance hooked up. I also put a vaccum pump to the distributor to hold the advance on the vaccum drop, also did nothing. I got the car from a friend who had it sitting for four years, but the points looked like they were rather new, it had a lot of meat on the contact surfaces, and didn't have much of any pitting, lookied better than a supposedly rather new contact my friend had. I also starts up within the first turn of the crank.
I had a similar problem and it turned out to be one of the weights in the distributor was egged out and the springs were bad. Just an idea. Kurt
