one lean plug

[Anonymous]

howdy friends... you may recall posts from a couple months ago when we were discussing damage my engine suffered to pistons 3 and 4 presumably from detonation or a lean condition. Had the engine (200ci) rebuilt, and upgraded to a durasparkII. Also switched the carb jet (1940 style) from a 61 to a 68. Welp... the #4 plug still looks lean with about 500mi on the new egnine. I've got a Holly/Weber 32/36 to try, but I can't see how one plug could run lean because of a carb? Had all the mating surfaced re-faced. Had an experienced ear listen and reported nothing unusual... Did a timing curve as recommended on this site on previous posts, have timing set at 8 deg BTDC and it advances up to about 38-40 total at about 2500rpm. Perhaps the carb has a vac leak. Any thoughts??? David SoCal

 

[CobraSix]

Did you have the head rebuilt?

My best guess would be that you may have something blocking #4. Usually #3 and 4 run richer on the log head then any other cylinders.

Slade

 

[Anonymous]

they went through the head, I suppose you could say rebuilt it, took it all apart and replaced one valve they said was no good. I suppose I'll have to ask more specifics.
I can't imagine what could block the flow to the cylinder? Thanks..