In higher revs the engine randomly stops and starts firing.

[WrenchWreck Repeat]

I am having an issue with my 2018 MT-07. When I get into higher revs, the bike gets jumpy as hell losing its ability to accelerate. It acts as if the engine randomly stops and starts firing. So far, I have replaced the plugs and ran fuel injector cleaner through it. It has a brand-new clutch that isn't slipping. Below is a link to a video I took displaying what it is doing. Sorry for the poor audio quality. Does anyone have any suggestions or have any experience with this issue? I would greatly appreciate any help!!!

https://youtu.be/btAJRqtPvVU

[M. Hausknecht]

What did the plugs look like; whitish, tan, black? What, if any, mods to the motor? Mileage? Does the problem clear up above 8000rpm or so, or are you unable to get there? Does this happen in all gears or only some gears? Enough fuel in the tank? Was mechanical work done on the bike and then the problem started?

It appears you're describing a misfire in the vicinity of the motor's torque peak. It is likely either too rich or too lean (my guess, without more info), or weak spark. More info will allow us to help you more effectively. I can't tell anything from the video because I can't hear the motor over the wind noise.

[WrenchWreck Repeat]

1. When I replaced the spark plugs, the old ones were in between tan and black. Since these were replaced, the issue doesn't seem quite as bad, but still exists. I'm not sure exactly how much better it is because I don't want to keep pushing the motor. It seemed better and then did it once again and I quite trying since issue was still there.

2. No mods have been done to the motor.

3. The mileage is right under 8,000.

4. When I first take the bike out, I can get to 8,000 rpm and maaaaybe go above that. The more I ride it, the more it does the issue. Takes 5-10 mins to get to where it doesn't want to go above 6,000 much.

5. This happens in all gears.

6. I have tried riding it with the gas tank anywhere between 100% and 50% full.

7. The bike was laid down last may. Rode just fine the rest of last season. Around October the crank case cover was replaced since it was scratched. It had been rode another 500 + miles since then. hasn't done more since winter hit after that. Sat all winter properly stored. The issue started around it's 5th ride of the season.

8. I can do a better video tonight if necessary. I can start from a cold start and drive around until it starts happening while trying to avoid wind noise. Is this worth it?

And last but not least, Thanks!!!

[mossrider]

Double check that your plug caps are on all the way.

Loose caps can cause intermittent spark under load or at high rpm due to excessive vibration.

I used the handle of an inverted hammer against the caps so I could get a good mash on em.  The handle length gets you past the frame backbone for working room and the head makes a good handle. 

Edited April 8, 2022 by mossrider

[wollerms]

Probably not your issue but I had an Aprilia that would start bucking and slowly get worse until it would not accelerate. Shut it off and let it sit a minute and it was fine again for a couple of miles then start bucking again. Fuel pump filter screen in the tank would clog up with dirt (fine grey sand) under pressure and impede flow.  I had to remove tank, drain, and clean it all out. I never brought gas from that station again.

First time it occurred; I was going 80mph in the left lane of a busy freeway......................................

[M. Hausknecht]

1 hour ago, mossrider said:

Double check that your plug caps are on all the way. 

I used the handle of an inverted hammer against the caps so I could get a good mash on em.  The handle length gets you past the frame backbone for working room and the head makes a good handle. 

 

Just now, wollerms said:

Probably not your issue but I had an Aprilia that would start bucking and slowly get worse until it would not accelerate. Shut it off and let it sit a minute and it was fine again for a couple of miles then start bucking again. Fuel pump filter screen in the tank would clog up with dirt (fine grey sand) under pressure and impede flow.  I had to remove tank, drain, and clean it all out. I never brought gas from that station again.

First time it occurred; I was going 80mph in the left lane of a busy freeway......................................

Two excellent suggestions here. One goes to the possibility of a weak spark, and one goes to a lean condition when fuel demand is at its highest. As you describe your spark plugs, their condition suggests an overly rich mixture (if darker than a light tan or light grey color) but that appearance is also consistent, in my experience, with a weak spark. The fuel pump is fairly easy to remove from the tank, and disassemble sufficiently to clean the netting used as a filter and then reassemble.  

 

[Triple Jim]

Maybe the crash did something to the sidestand safety switch or its wiring (or other wiring somewhere), and in high wind it starts causing trouble. 

Is the problem the same in a lower gear when you're not moving as fast?

A severe problem like you're describing points to both cylinders quitting at the same time, intermittently, so I don't suspect a problem that's specific to one cylinder like plug caps.  Caps could cause trouble, but probably not synchronized with each other.

Edited April 8, 2022 by Triple Jim

[Shyan]

On 4/8/2022 at 9:26 AM, WrenchWreck Repeat said:

I am having an issue with my 2018 MT-07. When I get into higher revs, the bike gets jumpy as hell losing its ability to accelerate. It acts as if the engine randomly stops and starts firing. So far, I have replaced the plugs and ran fuel injector cleaner through it. It has a brand-new clutch that isn't slipping. Below is a link to a video I took displaying what it is doing. Sorry for the poor audio quality. Does anyone have any suggestions or have any experience with this issue? I would greatly appreciate any help!!!

https://youtu.be/btAJRqtPvVU

My wild guess should be the Fuel Pump... suggest to get it check 1st as it happen on all gears and high rpm and the haywire fuel pump feed not enough fuel into the system..

[00RAH]

Your throttle seems to be in a different position from stock. Could it be youre not getting a full twist on the throttle and its not opening all the way?

[wollerms]

Wrenchwreakrepeat, did you ever figure out what the problem was?

[sweetscience]

Also check clutch lever safety switch.  Seems like your check engine light is on.  Get it scanned.

[cornerslider]

It may seem like a long shot, but you mentioned you recently changed the plugs.... That means you most likely removed the fuel tank. Is it possible the fuel line (or breather/vent line to the tank) may have gotten "pinched" somewhere during the reinstall of the tank? I've seen this on multiple bikes in the past- (never on an "07" though).  My gut says it's something pretty simple. It looks like there is a yellow light on the dash in the video. Is that the "check engine" light, or the ABS light? I have a non-ABS FZ-07, so I'm not too familiar with dash configuration on the MT-07? 

[WrenchWreck Repeat]

Thanks everyone for the responses!! I eventually gave up and took it to the dealership. It confused the hell out of them for awhile too. They contacted some advanced Yamaha techs to look at it and they eventually found the problem. It was the stator. They told me it needed a new stator but I didn't want to pay their prices; almost $1000 for everything lol.  I took it home, pulled the stator cover off, and found a short in the wire that runs to the stator. I spliced the wire, soldered it back together, and applied shrink wrap. I then put everything back together and it has run great ever since.  Spent $100 for the diagnosis and maybe $10 at most for shrink wrap, wire, etcetera.  Hopefully this information can help someone else down the line.

[Triple Jim]

It seems a little hard to believe that they really thought you needed a whole stator, especially since you were able to find the problem with the wire without too much anguish. 

[mjh937]

It does not seem hard to believe to me.  I find that dealerships usually like to just replace things instead of fixing them.

[Triple Jim]

Just now, mjh937 said:

It does not seem hard to believe to me.  I find that dealerships usually like to just replace things instead of fixing them.

The hope is that they weren't trying to pay for the time they spent by purposely doing more work than it needed.

There are places that will rewind stators for a couple hundred bucks, too.

Edit:  I just checked Partzilla.  A new stator is $210.

Edited August 26, 2022 by Triple Jim