Lars,

Got your paper on tuning them this week. Just did that and put it on the car.

The carb hasn't been run in a couple of years, so I don't think it is a tuning related problem.

The problem is I'll rev it up and the rpms will jump up and on the way back down they'll stabilize around 2000-3000rpm and stay there. I can get the rpms to drop after playing with the throttle. The primary throttle plates are closed, the secondaries look closed.
Could the power piston be sticking?

Any other suggestions? Troubleshooting procedures?

Thanks for the help.


p.s. Your paper on Tuning the q-jet is great!

 

Hi Mike I had the same problem. I found the rod to the acc pump was catching slightly on the throttle linkage. Also Lars had helped me and suggested the linkage on the fast idle may be hanging up. Of course Lars is the master and I hope I did not just misquote him.

 

Mike -
A stuck/defective power piston setup will not cause a hi-rpm problem as you describe. I'd look for one of the following if I were you:

First, get the problem to occur. Then shut the engine off (it may diesel and run-on a bit when you shut the ignition key off at 3000 rpm, but it'll die eventually).

1. Take a look at the fast idle/choke linkage. See if the fast idle screw (located on the passenger side of the carb under the choke linkage - head facing forward) is on one of the ramps of the fast idle cam. The fast idle cam should freely move up and down, but it's easy to get it jammed when assembling the carb. The cam should be dropped all the way down so that the fast idle screw is not in contact with it. Check the rest of the choke/fast idle linkage and assure that it's operating freely.

2. Check your accelerator pump rod where it attaches to the throttle linkage. It's possible to get the rod partially inserted into the key-lock hole, causing a bind.

3. Check to see if the throttle is fully closed or not: is the throttle stop resting up against the idle speed screw on the driver's side? If it's not, you simply need to keep looking for the mechanical obstrauction/bind-up that's keeping the throttle open.

4. If you have verified that the thottle really is all the way closed, up against the idle screw, you have some massive vacuum leak. This can be from the PCV port, power brake port, or from using an incorrect base gasket. However, since you're able to get the idle down by playing with the linkage, I tend to believe that you have a sticky linkage problem and not a vacuum leak situation.

5. Be sure to check the throttle linkage itself: Disconnect the throttle cable from the carb and see if this allows the throttle to close further. Often, the cable itself is an issue.

If you continue to have problems, let me know, and I can give you a call and chat with you about it if you'd like.

 

Thanks Lars, Gonna go out and play with it now.

 

Looks like it needed a night to unstick everything. Went for a ride to get the throttle to stick, but it won't.

I forgot how much torque I had! The edelbrock and holley don't compare to a tuned Qadrajet. If The edelbrock was mine, I'd spend some money and tune it to see how well I could get it working. The Holley, which is mine, is just way to big for a small block.

Now of to tune out that of idle hesitation.

Thanks for all the help Lars.