WR400 hesitation on high revs

After about an hour or two of riding I got into some slow 1st gear single track, when I emerged the bike hard a very bad hesitation when I got on the throttle hard.

I changed my oil today, used Mobil 1 Gold cap 15w 50. I've always used the red cap but they were out. When I got home it I compared an old Mobil 1 bottle and they appear to be the same, full Synth 15w50 (so maybe the cap just changed colors :applause: ). This is the only mod I've done in the last week.

Also, I noticed some oil on the left bottom frame. Some if from the oil change but it looks as though some is comming out of a breather hose on that side.

Could all these factors be linked? Are they obvious signs that something is going wrong? 4Strokes are rather new to me, I know I need to adjust valves but what else should I do?

Oil from the breather hose, a little bit, is OK...LOTS of oil is bad. What year, how many hours will help with the diagnosis...

Oil type won't affect carburetion...sounds like jetting, maybe an accel pump adjustment.

I was thinking the same thing. There is a few drops of oil on my garage floor, VERY little. So I think I'm ok there. Ive had it for about 2 months now and am going to proceed with a valve check/adj. pronto!

I'm also pulling the plug on it today to check for fouling. It runs great, so I never thought it to be to rich, but maybe those very slow tech trails were enough to foul it up. :applause:

Just pulled the plug and it was perfect, nice choc. brown. Made sure the plug cap was on snug, put her back together and took it for a couple laps around the block. Ran great, no hesitation at all.

Does the big WR400 have issues with overheating in trails? It wasnt a hot day and my coolant levels are up to par. I do have Devol guards though.

I'm stumped.

Are you sure it wasn't hitting the rev limiter? I know this is a dumb question, but it could be a possibility. Hope this helps,


uhh, no. :applause:

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