Hesitates on launch from light

[Charles P.]

A 72 with a stock quadrajet I was driving recently seemed to miss a beat occasionally when starting out from a light. Not a huge problem because it only happened when starting out ant only a "heartbeat" or two and after that pulls as good as a tractor. I run premium 93 octane. What would be the most likely culprit(s) for this. I have yet to check the fuel filter but it has an amazingly clean fuel tank. Floats/carb rebuild time? Thanks

[Joe C.]

Re: Hesitates on launch from light

Accelerator pump problem.

[Michael W.]

Re: Hesitates on launch from light

or secondary air valve problem

[Wayne W.]

Re: Hesitates on launch from light

It maybe checking for on-comming traffic, or maybe the fuzz.

[Terry R.]

Re: Hesitates on launch from light

I had a new '72 El Camino with a quadrajet, every so often I would have to put a little Berrymans B-12 Chemtool in the bowl vent to get it to come off idle without stumbling. It acted like the accel. pump wasn't working but it was visually. Have fun Terry Robertson

[Gary C.]

Could be vacuum leak or idle circuit problem

as well. Good luck, Gary....

[Robert Willis]

Re: Hesitates on launch from light

Mechanical or Vacuum advance sticking ?

[Jim T.]

Re: Hesitates on launch from light

Charles if your 72 is original the engine was designed to use lower octane. Used 93 octane in my 85 (more computer assisted ignition) until I got additional data from GM on my engine stats. It was designed to run on 87 octane according to the specs and I started using 87 octane. The 85 runs great, really have not seen any performance difference between the different grades during the last 5 years, just less costly at the pump. 85's compression ratio is 9-1.

[Joe C.]

Re: Hesitates on launch from light

The '85's ECM optimizes the spark advance......so it will advance to the point of detonation, then back off a tad.
When my '85 was brand new, I was surprised, if not embarrassed and pissed (gas was about a buck/gal then)at the thought of a CORVETTE running on regular unleaded. I tested the fuel mileage using regular, and hi-test, and calculated the cost-per-mile for each grade. The cost-per-mile was actually LESS with premium fuel. I've been running premium ever since.
Besides that, because the ECM likes the extry octane, and bumps the timing to show its gratitude, the engine responds by making more power

Joe

[Charles P.]

Re: Hesitates on launch from light

Is their a quick fox for the accelerator pump or is a carb rebuild in order? If that does not fix it move on to repalce the vacum advance on the distributor?

[Bill E.]

Re: Hesitates on launch from light

My '74 acted the same way on fast acceleration from a stop. It would also stall when first started. I changed the fuel filter (it was clogged) and that solved the problem. My theory is that if the filter is clogged the by-pass doesn't operate fast enough on start-up or acceleration but once open the car runs fine.

[Patrick H.]

Re: Hesitates on launch from light

Adjusting the secondary air valve takes but seconds and is where I'd start first.

After that I'd think about swapping the accelerator pump IF you're familiar with the internals of a Q-jet.

The third thing is that I've found many base motor 72 act like yours to some degree. So, some of it may be "natural" if the advance curve and other issues are still stock.

Patrick