I just installed a K&N, a pipe, and a Dynojet kit on my 660 GRIZZLY. There was a noticeable power increase on the low end but it seems like I've lost some mid range and top end. After riding an hour or so I pulled the spark plug to check for a lean/rich condition. The base of the plug where the threads were located was black but the tip of the electrode was light grey. This brings me to my first question.

1. What color should a properly jetted 4 stroke's spark plug be?

2. Does a lack of mid range through top end power (no noticeable smoke) indicate a rich or lean condition.

After cleaning the plug I did a series of plug chops to determine where in the fuel circut there could be a problem. My results where:

1st Run: Idled for approx. 10 min. plug color: greyish brown
2nd Run: 1/2 throttle for approx. 1/2 mile plug color: light grey
3rd Run: full throttle for approx. 1/4 mile plug color: light grey

Thanks for reading my post and any help would be greatly appreciated!

 

well i am no expert but ill try to help, if you lost some mid to top end i would
say you need a bigger main jet. did your kit come with a pilot jet? the pilot jet
controls your mid. your plug should be light brown.

01 BLU 660R

 

I am not familiar with the grizzly setup, but maybe I can help. first off here is how the fuel circuit works air/fuel mix screw-->idle maybe a bit more, pilot jet idle-->1/4, needle jet 1/4-->3/4, and main jet 3/4-->full. Your description suggest a problem with the needle jet. some things to try: if you have holes in your airbox try taping them closed (richen the mix) you can also try that on the filter itself. hope some of this helps

 

Thanks for the suggestions. I'll richen up the needle jet and put the 160 main in that came with the kit (running a 155 now).