OK, I ordered a rebuilt Q jet from Auto Zone. It is spec'd for a 1970 Skylark 350 4 bbl with manual trans. I have an assortment of Sec rods and hangers, and plan to go richer on the rods and "higher up" on the hanger hole for earlier secondary enrichment. Do you think I'd need to mess with the primary circuit? Or anything else? My specs are High Comp 350 .030 over .480" I lift, .500 E lift 112 lobe centers, 278 I dur, 282 E dur advertised. T/A Intake, Hooker Headers 2.5" exh that FLOWS, home ported heads, low rear end gears. The 750 DP Holley I have worked very well, but is now giving me sticky float issues. I always wanted to try to go back to a Q Jet anyway, but an slightly concerned about giving away some HP. Thanks! Andrew
The '68-'70 350 manual carbs all came with a .073 main jet and a .043 main rod. In my opinion that's plenty fat enough for most 350s.
I would run it out of the box and cross your fingers (after making your secondary changes, of course), but be prepared to go into it. Quality control on assembly line reman carbs is not the best. I got a Holley-rebuilt Q-jet and found the wrong power piston installed. Worked a lot better after I discovered/fixed that.
Wow. That's a weird problem, and one that I don't know if I would have caught. What were the symptoms that you had before you fixed it? Also - were the throttle shafts fairly tight? My old Q jet is loose as a goose.
It had NO throttle response. Turns out they used an earlier power piston without the APT pin sticking out the bottom, so it was sitting way too deep in the hole, and taking too long to come up on the power circuit. Throttle shafts are fine, I think.
Ditto on the assembly line rebuilds...better off going over a decent core and building/kitting it yourself.Later,Tony.
I understand. My old q jet must have the proper piston, then. It has the peg sticking out of the bottom. Funny thing is that I do have a weird lean condition at part throttle anyway. Idle is ok, and full throttle seems ok, but part throttle, the car acts like it's trying to breathe through a 1bbl made for a lawnmower.
This problem sounds like a lean off-idle condition. You might try adjusting the adjustable part throttle slightly richer, though I think it will require some different metering. How does the heavy throttle metering feel before the secondaries open? If the entire primary system feels lean, a one size larger jet might help. These changes should be made one at a time, in order to keep track of the changes made. Are you sure that the power piston is not stuck? These carbs were well known for this. Be sure that this is not the case before making changes. Let me know... Ray
Turns out that it has lean primary jets and rods. My fault. I have a Q Jet on order at AutoZone, which I hope to try out tomorrow. Yes, my fingers are crossed, since this is a Champion rebuilt carb. They don't have that good of a reputation
If you have a loose throttle shaft, you'll always have idle & tuning issues. Try the link below. He can rebush the throttle plate. (Ohio) http://www.cliffsqjet.com/ The wear on the throttle plates was accelerated by GM's mounting of the return spring facing rearward. Between it and the throttle cable, it acted like a saw over time. I always mount my return springs forward now, towards the radiator.
