Originally posted by RClover
The black diposites on the alumminum piston usualy means trouble with heat above 250 F'.
For me that is 50 F' hot and I get all the power in 200 that others get at 250. so you probubly need to tune properly or add fuel to the mixture.
Got this off from another forum, is this guy telling correctly?
I have those dark brown deposit on the piston head while my pipe still spitting fuel from stinger, and the car not very fast.
Is that caused by too lean..?
It could actually be the other way around. If you run too rich (4 stroking) the motor will run too hot. If this is the case the top of the piston will look a dark brown colour like it is burnt. I any case, it sounds like you need a tune. Set the motor back to factory and then bring it out another turn top and bottom. Creep up on your tune from there. It also sounds like you may be too lean on top, and too rich on bottom.