I recently bought an 04 WR450F from a friend. Because it had been stood for 5+ months I immediately added 1/2 of a tank of fresh fuel to the 1/2 that was already in the tank. The bike rode fine, albeit with some initial minor backfiring and a fair bit of popping from the race exhaust (not yet jetted).

However, when I changed the oil filter, oil, air filter, and spark plug the mid range power is now hesitant/jolty, although when I open her up she's fine, or if I accelerate grunty in a high gear it's fine too. It just seems to be the mid range.

The only thing I can think of is it's either crap in the carburetor, or it's because I've gapped the Iridium spark plugs to 0.8 mm instead of leaving the pluf pre-set

Any suggestions guys? Help much appreciated...


Cheers Ian.

Sorted the problem. It was bad fuel.