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stumble on accel./1964 394


Guest mortsciguy

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Guest mortsciguy

My 64 Starfire has a slight stumble on initial throttle. If you hit it hard it even does a little internal backfire. Timing is set at 3 to 4 degrees BTDC, to compensate for 92 octane premium. Car is running a Pertronix Ignitor. Vacuum is good. I suspect carburation, the accelerator pump in particular.

Once the big beast is rolling down the highway, life is good. Less than agressive throttle application is much smoother. Any help/ideas would be appreciated.

Kelly

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Guest mortsciguy

Thanks Pontiac 1953. Time to head out to the garage to try an idle mixture tweek, before I move on to accel. pump. I hope an increase in richness will cure stumble.

Kelly

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With the engine off and the air cleaner (top at least) removed look down the carb throat and excercise the throttle. You should be getting a small solid jet of fuel. If that's happening and you still have a stumble on aggressive acceleration, check your manual and see if there is not a longer pump stroke adjustment for the accelerator pump. Many carbs can be adjusted that way. Joe

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Make sure the distributor advance weights and mechanism is free and operating.

A slightly low float level will cause this headache too, as will a 4GC with the wrong gaskets between throttle plate and fuel bowl. You might make sure the secondary throttle valve is not opening too quick (or too slow) on hard standing start acceleration.

Then again I never did get that off-line stumble totally tuned out of the blue Starfire's original 4GC. That one got so bad at one time it was impossible to get going from a standing start on a hill, and taught me a valuable life lesson: When a 4GC is good, it's great. When it's not, throw the thing in the trash.

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Guest mortsciguy

Can anyone verify the application code on this 4-Jet? Tag has it as 7024050.

Sound correct for a 64 Starfire 394?

Kelly

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Try setting the timing to factory specs. It sounds like you don't have enough advance at idle.

My 1961 Starfire manual calls for 7 1/2 degrees BTC with premium fuel. At my altitude(6500) feet I am running at 10 degrees BTC. Runs great at all speeds and gets good economy @ 16 MPG on the Interstate. The car has pertronix installed.

Good luck, Dave

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Guest mortsciguy

Thanks, Dave. That will be easy enough to try. Today, it belched a big blue flame out of the carb when I was tweeking idle mixture... timiming is what jumped out at me. But I have been so nervous about piston detonation with current fuel, I am running less than spec on advance. I'll give it a shot.

Kelly

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Guest mortsciguy

Dave,

Set timing to specs. No spark knock . More power, less stumble... a lot less!

Thanks to all for feedback.

Kelly:D

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Guest mortsciguy

Thanks again, Dave. I am only about 750' above sea level. I might bump it up a few just to see what it does.

Kelly

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