Hot Plugs!!

[rossthaboss11]

tuning up my ski and the motor and head arent hot, not nearly as hot as its been in the past. but the plugs are very hot to the point where water sizzles off of them. its a stock head with stock compression on a 650 sj. so im not sure if its lean or rich. the plugs are a darker brown but they arent to new. also im at 145psi compression, how much do i mill off the head to get about 175 psi?

 

[SharkB8]

I can't really answer either question, but you should post what type of plugs you're running. If they are NGK plugs, I believe B8HS is the recommended plug. (Or maybe BR8HS? Basically the same plug.) The 8 is the heat range number. 7 is hotter, 9 cooler.

 

[rossthaboss11]

does the 7 meaning hotter mean that it can be run at hotter temps? i do have the NKG BR8HS or whatever

 

[SharkB8]

A 7 produces more heat. If you're jetting your ski and starting on the safe (rich) side, running a hotter plug will help burn off the excess fuel/oil. I ran a 7 in my 701 for the first few tanks of gas until I remembered, then switched to an 8.

I'm pretty sure you can't tell whether you're lean or rich by how hot the plugs are.

If you're running a stock 650 with stock carb, just put it back to stock jetting and you know your jetting is good.

I would guess 25 thou off the head for an extra 30 PSI of compression but it is only a guess. I wouldn't start modify anything though until you're sure about the jetting. A stone-stock 650 would be a good machine to go through the jetting process on. Very forgiving.

 

[rossthaboss11]

yea i was also thinking about 25 to 30 thou as well i did a little research. good guess!! this isnt a stock ski however. 61x cases, 46mm carb, riva red pipe, msd, all tthe goodies. but i know these 650 cylinders are forgiving so all i need now is more compression and to be tuned and im set. thanks for the help. i just dont know why the plugs are so hot and nothing else really is