tru-blue 442

Has anyone ever seen this type screw in this place on a quadrajet?
All the ones I have ever dealt with had a plug, like a small frost cap
in them. Any idea of the function?

rob1960

That's the primary part throttle adjusting screw that someone modified. You're correct they were set at the factory & then capped off with a staked in plug.All the early q-jets, except the '70 256-255 "W30/31 carbs, had them. It should work out well for you since you can now "tune" the primary circuit. If it's too lean your car will surge at part throttle,just turn it in a little at a time to raise the stop & road test it 'til it runs smooth. Of course if it's too rich it'll suck gas like a pig. I'd put some kind of sealer on the threads so you don't get a vacuum leak. If you know anyone local that has a dyno with an exhaust analyzer that would be the way to set it up.

tru-blue 442

Thanks for the info Rob. Any idea how far to back it out after turning it all the
way in to get started with the tune?

rob1960

That's a pretty long screw. I'd probably start by turning it in until it contacts the metal lever stop piece & you can feel it start to raise up(since the factory setting was lost it's trial & error). Maybe go another turn & see how it runs. You should be able to get it close just by running the engine off idle(around 2000rpm) & turn it in or out until it runs the smoothest. Then take it for a road test. I did it this way on my girlfriends '76 Salon. The '76 carb is a little different as it has a separate part throttle jet & metering rod. The car's cat-con was long gone & I put '73-4 dual exhaust on it. It was way lean & ran like crap. I raised the stop screw(the service manual says do not adjust!) a little at a time & the car runs super.

tru-blue 442

Thanks again sir. It will be awhile until it's on a driver.