I have had my carb rebuilt not long ago, and I would like to adjust the mixture screws. The covers have been removed so they can be accessed. I cannot see which hex? should be used. Any input would be appreciated.

 

If this is a computer-controlled one, don't bother. They have virtually no "authority". I'm not sure why they're even there. I just set them to 7 turns out (they're an EXTREMELY fine thread) and leave them there, on every one of those I ever build; then tune the idle with the IAB valve, which has MANY times the amount of effect that the screws do.

 

I agree with Sofa, the IAB has a huge difference on the CC Qjets. Just make sure your lean and rich stops are set at 4 turns and the MCS has 1/8" travel.

 

So the mixture screws do little on cc q jets compared to mechanical carbs? Do you know which hex size the are?

 

I think it's more like 3-4 from seated. You only need to move them if you run out of adjustment room on the iac.

And they're not hex. I dont remember what it's called, it's more like a rectangle. You get the bit when you buy one of those flexible-shaft carb adjustment screwdrivers. Or if you take the carb off you can use pliers to remove them then saw a notch in it to use a flat head screwdriver.

 

Alright Sparky, I just wanna know what the **** I'm doing. The guy who rebuilt my Q jet, told me he put smaller jets in it for better primary performance. He would adjust it if I got frustrated, but I would like to do it myself. It does have good throttle response. Better than before.

 

Double D - that's that name of the adjustment tool bit. Turn in clockwise until seated. Stock adjustment is set by turning counterclockwise 3 & 3/8 turns out. If it's running good might turn 'em in (count turns) and then turn back out plus a little more.

 

OK, the double D. The bits are not marked, but I noticed four of them are called hexes, and one double D Two are male hex bits, and to female bits which are hex design of different sizes. The other must be the double D. Why do you recommend turning them in first and then backing them out?

 

You turn them all the way in so you know your starting point. 3 3/8 yes that was the official number for my 85. I'd usually put them at 4 or 4.5 because the iac would be a little too far in on mine if it was at 3 3/8, but my shortblock had been replaced so maybe it had a hungrier cam.

 

I'll try your specs. I do not know for sure if the cam has been changed. It runs very well for a 5.0. Would I get any more performance if I went beyond 3 3/8 if it were a stocker?

 

No, it's just that when you have your dwell meter hooked up, adjusting your IAC to get your dwell cycle where it should be, if your IAC is turned in as far as it can go and your dwell still isnt right (I dont remember anymore whether you turn it in to increase or to decrease dwell), thats when you back the front screws out then readjust the iac. I think the manual says try about 1 additional turn at a time.

Theres something else that people do to increase fuel flow on the primaries, they adjust the lean stop screw or give the needles more than 1/8 travel or something. I neverm essed with that because my car didnt have any part throttle flat spots.

 

After the carb rebuild, I have no flat spots, no hesitation, no nothing. It almost runs as smooth as a fuel injected engine. Been very happy with performance. The mileage seems thirsty.