Q Jets Q's

[Clod_King]

I just got a Edlebrock rebuilt Q Jet, but idle while the choke is on is waaaaayyyyy to high. I don't have the Tach hooked up yet, but the engine sounds like it's on the highway... I can get it to idke nicely when I disable the choke though.


Oh and this is a divorced choke unit, and I do not have the choke in my hands yet. It was back ordered, and I'm still waiting for it to come in. So I have been operating everything by hand for now. Would the choke make a difference?

 

[tRustyK5]

If you don't have the divorced choke yet, then it's hitting the max choke step when you're setting it by hand. The high idle is generally controlled by a stepped cam, so if it's not terribly cold the choke may activate enough to hit the first step and only slightly raise the rev's. When it's really cold, it may hit the third step. That what you'll need to adjust when you get your choke assembly.

With temps as they are right now you could run without a choke no problem.

Rene

 

[Clod_King]

I had the truck running and warmed up, and set the idle as low as I could. I think I need to set it a little bit higher to get it running with out the choke though. Because right now if I kick it down the engine just dies.

So I need that choke to do any real permanent tuning then correct?

 

[tRustyK5]

Yes...

Rene

 

[Clod_King]

I got the choke. Can I only adjust the choke setting by bending the little connecting rod? And how do I know how much to bend the lil sucker?

 

[tRustyK5]

I've only ever messed with the electric choke style. Try it as is first, it may be close...

Basically there is a bi-metal spring in there. As the temp goes up the spring tries to unwind, which pulls the choke open and pulls the linkage off the high idle step.

With summer temps the choke should be not even completely closed when cold, and you should be able to watch the choke open relatively quickly. So, fire it up and let it warm up until the choke is completely open, then set your idle speed. Then you can start messing with mixture.

Rene

 

[Clod_King]

The engine still seems to be running like a banshee on first start up.

I have to do a bunch of stuff before I mess with the fuel mixture settings... I need to adjust the ignition timing, and that vacuum advance thing on the dizzy, and also fuel pressure. The fuel pressure is currently sitting between 5psi, and 6psi. I think it should be around 7, correct?

I'm dedicating this weekend to the truck, so I'll get the timing done, and I'll hook up my tach as well. That should be pretty helpful.

 

[tRustyK5]

5-7 psi is the right range. Carb's aren't terribly senstive to fuel pressure, as long as it's not too high. That can overwhelm the needle and seat and flood it out.

Rene

 

[Fordum]

Check to see what hits the fast idle cam on the side of the carb. Its the three step brass cam that is turned by the choke. On most of the carbs, its an adjustable screw.
So, you have an idle screw on one side of the carb, and a choke/fast idle screw on the other side.
You need to adjust that screw until it is fairly fast on the fastest step.
It may not have an adjustment, but most do.
J.

 

[K5dreamer]

well... my carburetor is invisible, so its really hard to work on...

but i had a 1977 oldsmobile with a Q-jet back in high school. first off congrats on getting the best dang carburetor ever made. If i ever run a carb again it will be a Q-jet design.

Now, if memory serves, my olds would have a really high idle at first start up, sounded like it was trying to take off. in fact if i put the car in gear and let off the brake that big ol boat would drive down the road at 15mph at idle until it warmed up, or untill i kicked it down with the throttle. Id assemble everything and test it before you start bending anything. from my memory of a decade ago, seems to be running the way i remember on my olds.

 

[Clod_King]

I'll check for a screw. But if I cannot find it. I'm gonna start taking pictures, and hopefully someone can point to it.

My '79 scottsdale never did this. Atleast not in the summer, that's why I am asking this.