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I have a strange problem with my jinxed 66 389. It has been overhauled bored .030, mild cam HO manifolds rebuilt tri-power, Pertronix Ign. 4 or 5 times if I got on it enough to open the carbs but not hard enough to brake traction the engine would then run rough and shake and act like it was flooded (loading Up) It would almost die. I could shut it off and wait maybe a half hour and restart it and it would idle smooth. It did this after the Pertronix was added and before and after the carb restoration. Is it ignition? all but the last time it did it getting on it. The last just cruising about 50 after driving about 30miles. Incidentally , I had Mikes Tri-Power rework the carbs -this man knows his carburetors.
 

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First I would make sure your choke is operating correctly,.......if it sticks closed at speed it will over richen the mixture.....

Next make sure your Petronix ground, inside the distributor is hooked up, clean and tight....Petronix is very susceptible to poor grounding

Next I would Re verify the Petronix gap.....10 to 60 thousands......your rough running could be misfiring at speed if the gap between the magnet ring and module is not set right.....

Next I would make sure your weights and springs are not binding up, and when you add throttle and rpm’s your timing lags back and won’t advance....when you mess with the Petronix ring and washers etc not that hard to bind up those weights........if they stick you could get those symptoms.

No problem at idle because they do not need to advance at idle.....only when you add throttle....

Some easy things to check out first,...could be other things, mixture, misfire, plug Wire routed wrong, cracked distributor cap, corroded rotor tip, etc, etc

Let us know how you do!:nerd:
 

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I would initially say it is a flooding issue only because if you let it sit (which evaporates the excess fuel) it fires right up. It sounds like it runs fine other wise, just when you stomp it.

I assume you have mechanical linkage on your outboard carbs and not the dreaded vacuum can activated outboard carbs.

Disconnect the end carbs and try it just on the center carb. As Lemans guy stated, when the engine is warm, pull the center air cleaner and take a look into the carb to make sure the choke is fully open. Then check to make sure it has tension on it so it isn't being sucked close when you open the carbs.

Who adjusted the valves? You could have a lifter pumping up and holding the valve(s) slightly open which could also do this. The lifter will bleed down after it sets.

Who measured the pushrod length when the engine was rebuilt? Machining of the bock/heads can call for a different length pushrod. Might be too long and cause the valves to hang open when the lifters are pumped at at RPM.

Incorrect valve springs for the cam. Weak springs or not enough pressure for the cam lift selected could be adding to the above mentioned valve related items.

If this all checks out, then I'd be looking at something electrical/ignition. Did you hook 12-volts up to the Pertronix conversion?
 

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"It did this after the Pertronix conversion....." I would re-install the stock distributor and see if it still does it. Ten minute job, and sounds like it wasn't doing it before you 'upgraded' the ignition. I run the stock points dizzys in all my old cars, and have been driving my GTO's that way for 40 years without issues.
 

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X2 on reinstall the old points distributor.

Sound like the pertronix is having a problem at higher RPM and the dwell circuitry.
 
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