I have a 2003 400ex. How often does the spark plug need to be replaced. It seems after severel hard riding trips some power is lost. The hill I could get up after I replaced a plug is almost to hard to climb a month later. The parts people claim I shouldn't have to replace that much. Anyone else have that experience?

 

when u take the plug off, what does it look like? Is it black? If it is, is the black shiny or is it like baked on the plug?

 

The spark plug was a dull blackish color with some brown. Hard to discribe. Looked somewhat normal. Definitly wasn't new looking. Is there a way to clean the carb with it still in the bike?

 

Why do you feel you have to clean the carb? That color of plug sounds almost right.
How often do you clean your air filter?

 

it seems like its fine but since u were saying its hard to climb a hill or something, it may be too rich.

 

You could use an iradium plug, the next time you replace the plug, they last much longer than standard plugs.
Hows the air filter looking?

 

I have a K&N filter which I clean at the beginning of each season. I looked at it and it still looks clean, nice red color of oil on filter. Maybe the fine sand of glamis passed into carb.

 

You should clean your filter more often than the beginning of each season (once a year?)
Clean it every couple of rides!