Thread: Black spots on driveway

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68 Chevy, 327, 4 barllell. When truck cranks it puts two big black spots on driveway, just under tail pipes. This is ofcourse carbon. What could be causeing this? Thanks, John.

Common floor coating behind a 371 Olds with J2 power. I just move the cars around to keep the coating uniform.

thats only a problem if shes doing that after shes warm...... when its cold it should run rich thats what the chokes job is, to choke it of air, once engine is up to temp it should pull off the choke and not be running rich anymore.... if it still does it... then you might need to adjust your idle mixture a little bit

Only on start up with a dead cold engine. Nothing spitting or smoking after warm up. Still a little rich, but haven't had time to adjust. Been sitting since November, but will be re-activated soon.

alright try leaning out your idle mixtures a little bit and see if that cures it some.....

My straight 8 was doing that on my old carb that someone had set up to use a manual choke instead of auto. A new rebuilt with an auto choke helped but not at first till I got the choke setting dialed in right which gave enough richness to run but not puke carbon. Had to back off the original idle flow settings to more lean too.