Wierd Idle???

[mudbog42]

I just had a new carb (q-jet) installed on my truck and this problem has happened twice now on cold startup. When I start the idle jumps to like 2000 RPM's and when I go to kick it down it doesn't budge and will sometimes stick at 2500 RPM's. I'm thinking that there is a sticking throttle linkage or something but don't know why it does this.

 

[stevos67k20]

is it a new holly? cuz those carbs piss the heck out of me with the electric choke crap. my little bros truck did the same thing and it grew out of it. same with my friends new 383, he had a holley 600 that didnt the same thing, but doesnt any more mysteriously. the only thing i can say is make sure you have a constant 12volt source going to you carb with the ignition on. my truck has a mechanical choke and i never use it. maybe you can remove yours and not have to deal with it????

or it could be your throttle linkage. again, my bro and friend had trouble with throttle linkage. they had to put a loop in it for the holley carb.

 

[mudbog42]

No its not a holley, its a quadrajet that I had built by jet performance

 

[stevos67k20]

ohh....maybe give them a call and see what the hecks up? try to disconnect you throttle linkage and pull it in and out to see if there is any binding. make sure you have it located near where it hooks up to the carb so its a better simulation. other than that, i'm in over my head. have you ever tried to let it warm up by itself? let it completely warm up before you blip it down. dont worry youll figure it out.

 

[dirtynails]

I think I read somewhere recently that the most commonly misadjusted thing on the q-jet was the choke. Let's assume for a minute that's all it is. Way down low under the choke coil housing is your fast idle set screw. It's hard to see, just as if they were trying to hide it. The screw on the upper area near the choke coil is for how wide the the choke blade opens. So ajust the fast idle screw to a lower setting I like about 1000 rpm on mine, I think the book says 1200 or 1300. The choke isn't going to let off to a lower rpm until until the coil figures its done its job. That only takes about a minute and a half or 2 minutes or so and then the cam weight will start dropping down while you are into the throttle a little bit. Sometimes the fast idle screw takes a torx or allen kind of fitting. Checker sells a carb adjuster "screwdriver" that comes with different fittings. I have one, it seem OK. Get that book "Rochester Carburetors" by Doug Roe, it helps a lot. If you are getting a superfast fast idle on one day and a slow one on another day be sure to check the linkabe for binding and any gummy build up. Spray with carb spray. If you have a 1 inch riser between your carb and your air cleaner that can sometimes be mispositioned and interfear with your linkage controlling the butterfly.

Enjoy learning about your q-jet, they are fun and it is becoming a lost art.

 

[Russell]

There is a small screw on the upper front passenger side of the carb, on top of a vaccum acuator's linkage. Back that off about half a turn or so, and it should drop the high idle to about 1200 rpm. The high idle won't kick off with the pedal unless it is warmed up enough, otherwise it'd come right off high idle as soon as you tried to drive, and cause it to bog like crazy.

Sounds to me like your high idle is actually working for once, and you think something is wrong, lol! I've actually only had one truck with a high idle that worked, and it was really nice! You could actually hop in, and go right after firing it up, didn't have to wait for 5 minutes till you could even think of putting it into gear.