"Lurching" while in 5th gear cruising

[jentzschman]

Went for a ride today and ended up doing a bunch of fire roads to get to the trail.

I noticed while in 5th gear, cursing pretty good, NOT WOT, but close, the bike felt like it was "lurching" forward or leaping a little. I tried to hold the throttle at a constant position and it still kind of felt like it wanted to just lurch, or "leap" a little at a time. Maybe it was just me not able to keep a constant throttle position, but thought I would ask.

I got home, pulled the plug and it look great. No signs of running lean that I could tell, if anything slightly rich.

I am running 40 pilot, 160 main, air screw 1 full turn out.

Bike is a 99 yz250. Has 13oz fww, 13 front sprocket, 50 rear. FMF Platinum pipe (not sure on a "type" it just says platinum) and FMF turbine core 2 silencer. Stock needle, as far as I know, clip at 2nd from top.

Just curious about this and thought I would ask.
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[TRD270]

I don't recall is your a 2 stroke or 4?

My WR would do this when I was at high elevations, ran fine from 4-7 k feet but 8k + lurch a bit will motoring around in 5th

 

[jentzschman]

I don't recall is your a 2 stroke or 4?

My WR would do this when I was at high elevations, ran fine from 4-7 k feet but 8k + lurch a bit will motoring around in 5th

The one thing I forgot to add.. lol
It's a 2T

I wonder if I'm slightly lean on the main?

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[Deleted member 12904]

You single track guys anything past 3rd gear is a fire road. We only did maybe 5 miles of "road" today the other road type stuff is what we call atv trails.

I honestly think what you where feeling was throttle. I always run in a taller gear to get ride of any of that stuff but with your bike being geared down you where in that touchy rpm range. For me it's worse when I stand since I don't feel like I have the same throttle control standing.

 

[jentzschman]

You single track guys anything past 3rd gear is a fire road. We only did maybe 5 miles of "road" today the other road type stuff is what we call atv trails.

I honestly think what you where feeling was throttle. I always run in a taller gear to get ride of any of that stuff but with your bike being geared down you where in that touchy rpm range. For me it's worse when I stand since I don't feel like I have the same throttle control standing.

Fire road was the best way to describe those long stretches.

Makes sense about the rpm zone and it being touchy.

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[Rot Box]

Check your chain tension. A chain that is on the looser side will cause the bike to do what you are describing.

 

[sixstringsteve]

Could it be your new clutch wearing in? I imagine it may need to be adjusted a bit more.

Or could it have been you hitting the power band where it wants to accelerate like crazy?

 

[rholbrook]

I know on the WR450s it is programmed in to do this. Drive me nuts but Yamaha has done this for cooling purposes. I doubt that is what yours is doing but on the WR's, you have to get an aftermarket CDI to fix it.