I changed the spark plug and the old plug was solid black. My 2001 trail boss is completely stock. Went riding after the plug change and noticed an improvement in power. Why is the plug so black? Is it running to rich? How do I go about making a carb adjustment if in fact it is running rich?
The air filter is new also.

 

i would say ur plug just needed changing. if i keeps fouling plugs then there might be a problem. i have a 300 2x4 that i change the plug about every month or so, even if it doesn't need it ( goes for my cars too) i feel a power improve ment everytime i add a new NGK hehe, if this keeps foulin reply back and we will c what we can do

 

black means rich. You need to lean it up. Open the air screw, lower the needle clip.

 

Also important is at what throttle range is it black at, because idling will throw off the reading anyway. Have you done a plug chop or does it just look black after idling a while?? Need more info to help you.

 

1) take it for a full throttle run at top speed turn of the quad stop and check the plug if it is black the main jet is rich drop back a size,
2) let it idle for a bit shut it down check the plug if it is black you will have to turn your fuel screw or air screw depending on the type of carb you have an easy wat to tell if it is located ahead of the slide tower toward the motor turn it in counting the turns till lightley seated then turn out staying have a turn in from the setting it was (ex if you counted 3 turns in till lightley seated then turn out 2 1/2) the more you turnout the richer the mixture will get .
And airscrew is located behind the tower toward the airbox and it is the opposite the more you turn out the leaner it will get so if it was 3 turns out you would go 3 1/2 .

Hope this helps