74
 

OK here's the deal.
74 still is breaking up on both sides under load.
Starts and runs fine until I give it 3/4 pedal or more.

New plugs and wires
New HEI distributor/set timing
New fuel filter and new gas

Carb is HP 700CFM DP
Turned mixture screws in and engine died, means power valves ok

I give up Any ideas welcome

My experience w/ that type of problem has usually been on the electrical side. Moisture in the dist., cracked cap, bad wires, etc. I know most of those are new but sometimes new parts are bad.

Shark,
It did this with the old stuff now it is doing it with the new stuff.
I would think even if I had a problem with the new stuff it would be a little different.

I am going to swith carbs and see if I still have the prioblem.

Maybe it could be vacumn but that would make the idle rough


This ones got me good

Didn't realize problem existed before new parts. Going back to old carb is a start. Or did the problem exist w/ it too.

BTW what's an HP carb?

This is a new problem that started after I had the Vet painted.
Infact it started the same day I picked up the Vet.

HP carb, I meant HDP Holley Double Pumper.

This problem on happens when I get heavy on the gas.
I am think that maybe the seconday power valve is sticking?

Anyway I am going to try switching carbs and see what happens.


Stay tuned

Don't know what mods you have on the engine but a DP may be too much carb. Is it a 750 cfm? Mechanical or vacuum secondaries?

If you've got a working Q-jet that'll fit the manifold, I'd try that.

700 cfm holley mechanical secondaries

Does it continue to break up if you stay in it or does it level out at a constant throttle? I'm think maybe the mechanical secondaries are dumping too much gas in it. A 350 at WOT takes about 650 cfm.

If I stay on it just keeps gettin worse.
This carb has been working fine for 5 years.

Sort of sounds like mine before I tore it down and found the rear cam lobes worn down. It just wouldn't run over about 3,500 rpm. Sounded like crossfire in the wires but they were new. Haven't reinstalled so don't know if rebuild fixed the problem.

OK, if anyone is interested I finally found out what was making my 74
break-up under a load.
This is after I replaced the distributor, set timing, new plug wires, new gas and re-gapped plugs and also went over the Holley 700 cmp, dp.

The problem was a KINK in the 3/8 rubber gas line that comes from the fuel pump to the carb.
When the guy in the body shop put my engine back in he replaced the rubber gas line with a different type of rubber line.
Very soft and wound up with a kink in it.

**** happens.

A rubber hose on the pressure side is a bad idea. There's a good reason that it was a steel line originally. Recommend you replace it w/ a steel line or at least use the hose used on high pressure FI systems.

Corvettes and fire don't work well together. Glad you found the problem.