Help with 306 problem.

Hello, New guy here with first post.

Need some help diagnosing a problem with my 69 302.

Motor has 2k on it after rebuild and was running fine until a week ago. Before that I had re-sealed and gasketed the intake due to oil leaks, removed 1” carb spacer, changed float settings on a new eddy 600, and moved the brake booster vac line from carb to intake tee.

Problem: When I start it up in the morning it idles fine. Get underway after a couple minutes of idling and it does OK until the nose pitches down (downhill to the stop sign, or applying brakes level or uphill), then it stumbles and starts to die until I let off the brakes and it recovers instantly. The interesting thing is that this problem gradually goes away as the engine warms up to 180 degrees (15 minutes) until it stops altogether. I figure it’s either float or vacuum, but it’s pulling a solid 17 inches at idle with no needle flutter. Ran great before I resealed the intake, blocked off exhaust crossovers, removed carb spacer, and moved brake booster vac line to intake tee from back of carb (have now routed that back to carb to eliminate that possibility).

Electrically grounds are tight, have spark at plugs, battery charged, cables tight, new ignition switch, and pertronix installed (swapped back and forth to points –has no bearing on this problem). Sorry so long but hoping this info suggests something.

Thanks for any reply.

Lowering the floats a bit should cure it....,,,,also, what are you running for fuel pressure?? With the blocked crossover, stumbling and bad idle cold is a trade off you have to make for not having all that hot air running under the carb!!!!

Thanks for quick reply Dave! It's a stock type but new pump which is supposed to put out 5-6 psi. I'll get a guage on it soon to check.

Y'know, I think you nailed it on the crossover. I had been having some exhaust leakage into the adjoining cylinders through the gasket due to wrong (way too much rtv) install on my first rebuild. To eliminate that possibility and living in FL I decided to block off the x-overs. I do remember now reading some posts about slower warm up without the heat.

I'll go ahead and reset the floats anyway since it was running fine before with the out of box setting.

Thanks again.