Recently fitted a new NGK plug to the bike as the old one was completely black and sooty. Now after only a couple of minutes riding the new one is getting to the same state...surely 4 stroke engines should be cleaner than the 'dirtier' variety?

A road racing mate of mine has suggested that the timing may be incorrect...I intend checking this as per the manual's instruction..I.E. with a strobe.

Any other suggestions?

Best regards, Mark.

Sooty plugs can be from a number of sources.

Incorrect ignition timing gives incomplete combustion.

Too big main jet gives too much fuel.

Oil leakage into cylinder from piston rings or down valve guides.

as a trials bike runs at low rpm they never get full throttle work for long which tends to clear out the residual oil.

Clearly you should eliminate the first two as problem areas before a strip down.

Might be weak spark

Have a look at

http://www.trialscentral.com/forums/index.php?showtopic=3789

This goes into detail a similar problem I had with my TLR

Cheers all...thanks for the suggestions..I'll let you know what I find.

Regards, Mark.