Lately I've noticed that when I'm just sitting there and I rev my engine it will backfire once in a great while. Also some brought to my attention that when I floor the pedal in a race I produce lots of black smoke. Any ideas on why this is happening or if the 2 issues are related?

 

Black smoke is carbon build up, not good but not bad. If it was white then your in trouble.

Backfire... Might want to try some fuel injector cleaner. Should help with the carbon as well.

 

do you think it has anything to do with nitrous or the fact that I use 91 octane

 

bump

 

plugs could be going. check the gaps to make sure they are still in spec .054

 

I just changed my plugs and gapped them at 37 to retard the timing

 

Black smoke = rich.

 

What causes it to run rich?

 

your Mass airflow cencor could be dirty causing it to read wrong and making to car rich. its not good to run rich or lean.

 

also my friends supra was running rich because a vaccum line fell off of the engine causing a sensor to read wrong, check the vaccum lines.