The Stovebolt Site Forums The Shop Area Engine Shop tuning question

well hi there ,new guy here ,just a question on tuning .a little history first i have a 1961 gmc 4x4 4 speed, with a transplanted 292 6cl .it is a .030 over bore 9.5 comp. stock pistons ,230 cylinder head with the smaller 1.72 and 1.50 valve's ,clifford 4brl intake langdon's cast iron headers ,holly 4460 4brl carb.i have not had it on the road yet but run's enough to drive it around the yard a bit ,will idle good but will break up under a loaded run . i have done everything i can think of verified cam timing and distributor timing ,even changed from hei to point dist.changed camshaft ,carb's no difference . any body got any wild idea's

Old dog,

Welcome to the Stovebolt. When I see a four barrel carburetor stuck on a 6 cylinder engine, I automatically blame it for most problems. This might not be accurate thinking though.

You said it breaks up under load. To me, this means it will come up to full RPM while just sitting in the driveway...no problem at all.

Things fall apart when you accelerate up a hill or when you lug the engine...is this what you meant?

If that is the case, ignition would be my first thought. If that particular carburetor has a circuit that responds to low vacuum that could do it too.

Knowing if the rig runs perfectly except when heavily lugged or loaded is the key to finding the problem. A little more explanation would help with the puzzle.

Stuart

yes when it is lugged under load,free reeving is no problem .it worked with a 600 holey when i had a rv cam in it ,just wanted a bit less gas .this is a smaller carb ,kinda like a economaster ,the same carb work's just perfect on my dad's 1940 1/2 4 speed with a 235 .the on extra performance part's he has is fenton headers with a offenhauser intake .it howl's on it.my vacuum is good i think about12 inches at idle ,the vacume advance work's also .

old dog,

It still sounds like ignition to me. I would check and/or think about replacing the plug wires....unless that was just done! Under a load, cylinder pressures increase. This means it's tougher for the spark to make the big jump.

If the ignition is marginal, it can fail under a load. It could still be a carburetion issue that dumps a bunch of fuel under load (low vacuum) and makes it difficult to ignite.

If the plug wires are old, that might be the place to start. I would also make sure the wiring to the coil was proper. If you had a HEI then you probably ran a full 12 volts. Did the point style coil you stuck on require this, or did it require a ballast resistor.

I have seen bad motor mounts allow the engine to torque over slightly under a load...just enough to tug on a primary lead wire and screw things up. This is a real long shot but it never hurst to keep your eyes open.

Good luck and keep us posted on your progress.

Stuart

well i had two dist.point stock, new point's ect wires cap . hei rebuilt with all new components and wire's no resister needed there is a resistor wire in the harness .mounts are not a issues new with fabbed cross-member for 292.