Stumbling at 4000-4500rpms

[Danno]

Just noticed it on the way to work this morning.

Had some problems yesterday with a non-start while warm at the gas station (vapor lock?). Had a lot of stumbling after I finally got it going again. Went home, opened up the dizzy and adjusted the points, then noticed that the wire to the condensors was loose. so I reconnected that. That was probably the problem all along, BUT I had already adjusted the point gap. Would a gap that is too small create a stumble at high rpms? Seems to be running smooth as butter at every other engine speed up to 4K.... Any Idears?

[Tappy]

i've had the same , but running on double webers , the jets where a little coroded ... so maybe your carb ?

[Danno]

I might be running a little rich right now, i guess I should have mentioned that. Checked plugs yesterday and they are pretty black, nothing horrible, but enough that i can tell.

[So Cal Mark]

the black plugs may be a clue to the hot start; fuel may have been boiling in the float bowl and flooded the engine after shut down. I'd pull the top off the carb and check float level and the needle and seat.

[rlux4]

Mark, please edify me. (In the intelectual sense.) When you say boiling in the float bowl, is that actual boiling, or a term for flashing, or what? And what causes it?
Ron

[So Cal Mark]

gasoline is made up of a variety of molecules; from heavy to light. The light molecules will boil at room temp, that's why gas will evaporate if left in an open container. That's also what causes vapor lock; fuel boiling in the line. If the float level is too high, vapors or liquid fuel can run into the venturi, then end up in the manifold and cylinders with the engine off. Makes hot restarts very difficult

[rlux4]

Ah so. And after the lighter molecules have evaporated, that's why you end up with a varnish-like goo?
Thank you oh venerable wise one.
Ron