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High speed misfire

June 12 2017 at 4:23 PM
John  (Login Argess)

I posted about this a week ago and at that time thought it was only at light loading. My mistake... twas coincidently when I shiffe4d. Let the throttle go higher and major misfire.

As I could hear gas igniting in the left muffler, (possibly the right also, but didn't hear that)and sort of firing out the exhaust. So I'm ruling out fuel.

Happens just after I pass 4500 rpm. Problem gets worse as engine fully hearts up.

I thought I had a bullet proof ignition system. Pertronix replacement for points as well as their recommended coil. New Autolite 45s... well... all is almost new, only a few years old, but only about 2000 miles on it all. Accel 8 mm spiral wrap wires.

I only checked one sparkplug so far. Porcelain was off-white (not bone white as running too lean). Electrode was same white from about halfway up electrode (vertical) and all of (horizontal) part. Rest, and circle around base was back.

So that's easy enough... just throw enough money at it and replace wires, coil, plugs, cap and Pertronix unit.

I'll check inside the dist cap next, then inspect all plugs, and eventually remove valve overs. I did have an outer spring break from this set once. Not likely, but makes me nervous.

Any thoughts? I just find it weird it pulls so hard until about 4500 rpm.

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