Tripower problem- 1964 1964 Pontiac GTO

I recently purchased a 1964 Pontiac GTO with Tripower on my 389. From the outset, I noticed a stumble at takeoff, and under light acceleration, a surge in every gear of my 4 speed, but more noticeably in 3rd gear at about 1800-2000 rpm. However, it only surges (or cuts out would be a better description) while trying to hold it at a cruising speed. I replaced plugs, wires, dist. cap, and had the center carb rebuilt. Upon rebuilding the carb, we found that one check ball was missing, the float level was too low, and the accelerator pump cup was split. We thought we had found the problem. However, rebuilding the carb, and replacing the ignition parts not only didn't cure the problem, it didn't help at all. Fuel filters have been replaced and the center carb seems to be getting good fuel flow. Any thoughts of where to look now?

 

What's your fuel pressure ? At idle and cruise when it's cutting out
Senseless to do anything carb related without knowing this .

Now a surge, a stumble, cutting out, a random misfire, and breaking up are all different things with different causes. Some more description will help

 

I have not measured fuel pressure, only due to the fact that upon acceleration, there is no cutting out at all. The cutting out definitely feels like a starvation for fuel rather than an ignition missfire. However, my next step was to check fuel pump pressure. The next step, after eliminating that, is to place it on a Dyno to simulate the actual cut out under load. My only thought was that someone may have run into this same situation before. The car also has an electronic module replacing the points in the original distributor. I have not elinated this as a possible cause either.

 

If someone doesn't solve this for you here, you should check out the PY (Performance Years) tech forums. If you can't get your help there you are in deep sh** as it's all Pontiac and just about anything you would want to know about a Pontiac can be found there!

 

Thanks Poncho60. I know about the PY tech forum, and I will definitely try that.
Thanks again.

 

First, are the carburetors original, or just something someone scrounged together to make a tripower?

If you have points and condenser available, you might put them in as a check. If that doesn't help, and you are in love with the electronics, you can always change again. Fully 50 percent of the "carburetor" problems we see today are from electronic conversions, generally in older vehicles with a generator which doesn't provide a stable voltage. It seems like most of these issues show up either at idle or at a constant speed. I don't ever recall an issue at WOT.

A compression test would eliminate a possible valve condition.

If the compression is good, the carbs are correct for the application and points/condenser doesn't help; I would check the orifice size of the main metering jets in the center carb. Use a set of orifice drills to measure the actual opening; pay ZERO attention to what is stamped on the jet.

It would also be useful to know the cam specs. LOTS of Pontiac guys go for HUGE camshafts that require MAJOR carburetor re-calibration. If cam specs are not available, vacuum readings at idle and the RPM with the surge would be useful.

Jon.