Engine going haywire between 2000-4000 revs, any ideas?


Zimmzimma

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Hi All,

I've done a but of research into the forums but can't find anyone with the same symptoms as me..

I've had the bike since new, fully serviced, now around 4,000 miles on the clock. It's always treated me right, but recently it's become a complete liability.

When in low revs, any gear, it's started sputtering like crazy. It now cuts out the often when rolling off, leaving me to have to release the clutch super slowly with revs high to avoid stalling. On two occasions it also did something that almost made me crap myself. While weaving through traffic it suddenly brought the bike to 4,000 revs and held it there even though I hadn't accelerated manually, nearly making me crunch into the back of a car.

The weird things are that it normally idles absolutely fine, and rides fine once you get above the 4,000 revs. Sometimes when you pull the clutch in it idles at 2,500 revs until you give the throttle a twist and it returns to the normal 1,200 or thereabouts. Other weird thing is that it's random. Some mornings it rides almost fine, other times it's jumping and stuttering constantly. No logic behind the differences - temp of engine etc makes no difference. I can literally ride it to the shops jerking like an idiot. I then hop off, buy the bread, turn it back on and it's almost totally smooth.

I haven't done anything to it (like service or modification) which might bring it on, it just randomly started and is getting progressively worse. It's like it's got some neurological disorder. Anyone had similar problems? The bike is totally stock so no weird cans or anything
 

stevecbr

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Im not aware of anything, but one thing to near in mind is the MT is fly-by-wire, ie the throttle cable doesnt directly control the fuel injectors. When you twist the throttle, the cables tell the ECU what you want, and the ECU will decide how much fuel the injectors lets through.
By the way you describe the issue, it sounds to me like an ECU problem, or whatever is used to open the fuel injectors (i'm guessing some sort of stepper motors)
A Yamaha dealer is your best bet, they have all the testing gear to see where the problem is. It could be loose connections, water ingress or failing sensors
Hopefully be cheap and easy to fix, let us know how you get on
 


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