does anyone no about how many turns out the idle/mixture screws should be on a Q-jet........factory setting perfered but what ever people think is good????

 

2 to 2 1/2 out from seated.

 

ok i have it our right now about 3 1/2

 

If it's a computer-controlled Q-Jet, set them to about 7 turns out (they're some VERY VERY VERY VERY fine thread), and epoxy over them or something; because they don't do anything anyway. That's not how you adjust the idle mixture on one of those.

 

yeah its a computer controlled......

then what are those screws for???

 

They're the "gross" metering system. The carb kit I got said 4-1/2 turns, which is where I put them and left them. The final adjustment is made with the IAB valve (idle air bleed) in the choke housing. You need a dwell meter on the 6 cyl setting hooked up to that green connector by the AC housing that doesn't connect to anything, adjust the IAB in small turns, letting it settle down before turning again, to around 30 degrees warm at idle.

 

so i have 2 1/2 turns, 7 1/2 turns and the i have 4 and 1/2 turns does any one else have any opinions......

 

Kid: what exactly does the IAB do ... i dont think i should mess with it... im just gonna leave it were its suppose to be...

 

They do about as close to nothing as possible; so pick the number you like, set them there, and forget them because they don't really do anything.

2½ is good for a non-CC Q-Jet. Leave that one out.

You've got 4½ from one carb kit, and 7 from another. Try something in between, like 5 or 6; and then leave them alone because they don't really do anything.

Oh, and did I mention; they have almost zero effect, no matter where you put them.

You WILL need to mess with the IAB. That's what actually controls the idle, and has a big effect on part throttle as well. Once you set and forget the useless screws in the throttle plate, you tune the idle with the IAB.

I'd suggest about 3 turns backed out from fully bottomed as a starting point; then tune from there until it's into the range where the ECM has control over it. Ideally you'd want it around 30° of dwell on a dwell meter reading to the 6-cyl scale; but different motors will run best with slightly different settings. As long as the ECM has enough authority to actually CONTROL it, i.e. the dwell is between about 15° and 45° at idle, it's close enough to work with.

 

i Dont have a dwell meter and also do you have a picture of the IAB that i can see.... Were would i buy a dwell meter...

 

Dwell meter=parts store. Do a search on some recent threads on adjusting the ccc-qjet and there's tons of info. Set your idle mixture screws between 4 and 7 turns out until the IAB affects dwell readings. My rule of thumb is higher than 7 or lower than 3 and the rich and lean stops need adjusting.

No need to epoxy over them, changes down the road may require some tuning of idle mixture to allow IAB adjustment. The idle mixture screws can help bring the mixture within the narrow band O2 sensor range for closed loop operation and IAB adjustment. Pretty simple system but there is more going on than a simple # of turns out that will work for everyone.

 

I picked up a new CC controlled Q-Jet from Jet Performance Products, rest my timing to stock, I think it was 9* BTC at idle and had to adjust my carb idle about 7 turns or so in to get my idle back to 800rpm or so (Auto Tranny). The way it came set it idled at about 400 and every time I revved the car at idle, when the RPM's dropped the car would die...it wouldn't catch itself to stay on. I don't know, it just seemed that 7 was a bit high especially since the directions said 3-4 full turns which just wasn't enough. Anyway, that's my experience with the Q-Jets. My old Q-Jet, just for the record, looks to be set about half as far in as this one is. Strange if you ask me.

 

i cant take the screws more than 3 1/2 turns out or else they pop out and fall out....

 

Non-computer controlled q-jets used a coarser thread on the idle mixture screws and 3 1/2 turns may be max travel. Sure you got a ccc?

Ozz1967 may be confusing idle speed set screw with the two idle mixture screws at the carb base?

 

Those are the screws im talkin about the two at the base of the carb once i get to about 3 to 4 turns it pops out!!!!!!

 

Following the directions that came with the carb, I'm pretty sure I got the right screw...I"ll double check just to make sure. I could have it completely wrong...

 

What carb do you ACTUALLY have? Part # please, not "stock", "off a Vette", etc.

Part # is on the driver's side of the fuel bowl casting, on the flange right above the sec throttle shaft; will have the format 702xxxx, 704xxxx, 1705xxxx, or 1708xxxx.

 

Ozz1967: I'm sure you got the right screw to adjust curb idle, it's just that chevyman is trying to adjust the idle mixture screws which are at the base of the carb and regulate the amount of fuel allowed into the idle circuits. At least that's what I think he's working on....

 

naf:

You're right, looking at my carb now I see the ones Chevyman is trying to adjust. Sorry to cause any confusion.

 

i will try and get the part # up tonight......
its on an 84 camaro z-28... i conferted the 305 to a 350......
it cost me 450 bucks... the guy at carquest told me the reason its so much money is because all the computer electronics it has on it!!!!!

would those idle mixture screws cause my car to have a hesatation????? getting on the gas there seems to be an hesitation......
also i have my timing at 4 degrees...Is that ok?

 

If the mixture is off, yes, it could affect it (putting to much gas in or too little). As for how much it cost, that's a bunch of crap. THe price difference shouldn't be more than $50 to $100 between the two.

 

wel l it seems like eveyrone is sayin to pull them screws out farther then they are..... but the screws dont want to go out... so im gonna take it back down there and have them look at it..... is my timing ok

 

I want to say 8* is where your timing should be. That's what my Haynes Manual says anyway. Mine is set at 9 and runs great.

 

ok ill put it to about 9 then.......