Black Gunk

[dirtyone30]

I have been noticing that after riding there is some thick black gunk dribbling down the end of the silencer. I have just changed 2 stroke oil to rockoil fully synthetic at a mixture of 40:1.
What can be causing this to happen, is it maybe a jetting problem, the jets are stock.
I am new to dirt biking and have only had the bike 5 months, i knew the previous owner and it was maintained well.

I have installed a DOMA pipe which is the only upgrade i can think of that may have made a diference.

The bikes a CR 125 2000

Thanks for any advice in advance

:thumb:

 

[23jayhawk]

Are you also fouling spark plugs? It is likely jetted rich if it still has the original brass. A pipe will often aggravate this be creating a stronger signal.

I'd suggest cruising through the CR/YZ/yada board & search for jetting discussions on a similar bike. That should be sufficient to get you started.

Don't be misled into thinking its the fuel/oil mixture ratio - separate issue.