A forum for owners of Yamaha TTR250 trail and enduro bikes!

Riggsb20 · Newbie

Black spark plug

Riggsb20 · Newbie

The bike is a 2005 model

Kev · Member

I would be looking at the carb accelerator diaphragm pump. I had terrible trouble getting my bike to run well, coughing and spluttering and a sooty plug. Cleaned and rebuilt the carb with a service kit and no change. It was only after replacing the diaphragm, which looked perfect with no splits, tears or other damage, that it ran well again.

Kev

mossproof · Super Guru

Oil burning will blacken the plug too. Sorry
Either passing the valve stem seals or the piston rings. Does the bike smoke much, either on startup or under load?
Air filter clean and exhaust system clear?

TTRfan · Super Guru

Shiny black plug tends to be a sign of burning oil, sooty black is usually a sign of a rich mixture.

If shiny black, is the engine using oil? If so, as Simon says, likely the valve stem oil seals need replacement and/or new rings or, at worst a rebore and next oversize.

If sooty black, does the bike run better without the airbox cover on? If so, that just may be a sign of a rich mixture.

Brian