black carbon buildup on sparkplug?

[macscr125]

my xr50 is hard to start evry once in a while. when it wont start i take the plug out and clean it and it fires right up. the plug is jet black with carbon residue every time. i have a bbr exhaust on it and the carb was never rejetted. what size jetting changes should i make? would the main jet change be enough or should i change the pilot? and what about the needle? thanks any help is apreciated.

 

[Jasle]

The pilot changes the bottom 1/3 of throttle the main top 1/3. I'd start with going down 1 or 2 sizes on the main and while there pick up 1 or 2 pilots smaller. Your definetley running rich.

 

[macscr125]

the jetting is stock though. i thought any time you add a pipe u would have to put bigger jets in it? could i try a couple of air box mods to get some more air out of it?

 

[Jasle]

unless your rings are so hammered you are burning oil... that could be your problem as well. valve adjustment could be off. have you done a compression test?

you never know til you try it. you could do air box mods but they are usually not reversible easy so once they are done they are done.