Low RPM stutter and hesitation

[cc]

Hi all,
Hoping to get some input to help with an issue. I have a 2015 bike with no mods and about 2200 km. When the bike is warmed up, between 2-3000 RPM, the bike feels like it misfires and stutters. Every time I have to start from a stop (you may assume I'm in 1st gear), the bike lurches and hesitates until it gets past 3000 or so RPM. It also lacks the power to get out of that RPM range. For example, if it is around 3000 RPM and I open up the throttle to half, it engine noise will sound deeper and nothing will happen for a second or two, then just take off. If I only give it enough throttle to stay between that RPM range, then it will just stutter indefinitely. The problem gets worse as the bike warms up and is almost nonexistent when cold. Another thing that happens that may or may not be related is that the bike idles inconsistently. It fluctuates up and down from 1000 to 1300. I've ridden another FZ/MT 07 and it didn't have any of these issues. Finally, the bike sat in a garage for nearly a year before I bought it. 
 
For some background. I live in Taiwan where there is a steep import tax on motorcycles over 250cc. As such, they are very expensive and not very popular. There are not many reliable or knowledgeable mechanics in my area and it seems my limited knowledge rivals that of the mechanics I've seen. Therefore, taking it to a mechanic without any idea of what is wrong has not been a good experience. I don't have a garage space so I can do very limited wrenching on my own. The three mechanics I've taken it to have done the following: fuel cleaner additive, fuel injector cleaning (took the injectors out and cleaned them), throttle body sync, chain tension, oil change, checked spark plugs (they look good), checked air filter (looks almost new), and checked connections ECU/TPS/various sensors. 
 
Thanks for the suggestions!
 
Edit: changed the spark plugs and it's fixed. Relieved it's over, but frustrated that the mechanic said it wasn't the spark plugs the first time I took it in.
 

[sorkyah]

The fuel injector cleaner and additive sound like temp patches that probably wont work
Throttle body sync was what i was going to suggest.
does your fz/mt have the vacuum operated intake flapper?
 
Maybe go through and make sure all of your connections, electrical and vacuum, are connected. A vacuum leak could cause stumbling at high load.
Bad gas/o2 sensor failure could also cause the catalytic converter to clog.

[cc]

Sorkyah,
It does have the vacuum intake flappy bit. The first mechanic went through and checked all the connectors and applied some product to help improve the connections. I'll check the O2 sensor next. 

[YZEtc]

Air filter condition?

[cc]

Forgot to say that the air filter looks new in the original post.
One of the mechanics thinks it could be the fuel pump. I feel like it's a fueling issue as well but it runs fine until it warms up. Seems like it's getting too lean at low rpms as it warms up. Does the ECU give it extra fuel when it's cold?

[rick]

You did not mention how many miles or if there were any mods done to the exhaust etc. If the exhaust has been replaced, look for leaks at the headers.
 
Guessing you have no error codes on the dash.
 
Yes, all motors need to run a bit richer when cold - especially at start up. This can be done by the ECU calling for more fuel squirts and by closing off air getting in thru the idle air control valve. If this is not working properly, the mixture will be too rich and the motor could stumble. Plugs would be pretty black though.
 
Yeah, sounded like an intake air leak to me as well until you said it was temp dependent. Also, intake air leaks usually result in a fast idle speed that the ECU will have a hard time dealing with beyond squirting more fuel to get the mixture seen by the O2 sensor correct. The ECU then tries to reset idle - lots of confusion results.
 
So, If it's temp sensitive, then I'd also check the air temp sensor and motor temp sensor and maybe even the TPS.
 
You'll need to check the O2 sensor's output right after start-up and after the exhaust is good and hot.
 

[cc]

No mods, 2300 km. I should have mentioned that the bike sat for almost a year before being sold to me.

[rick]

Hmm, that changes my mind.
 
Did it sit with gasoline in the tank for that year? In some respects, it would have been better if the tank stayed filled than if the gasoline was allowed to evaporate. Fuel residues are hard to clean these days. Just adding a fuel additive, like Sorkyah mentioned, may not be enough.
 
Sounds like the injectors were cleaned properly, so they should be OK.
 
There's no fuel filter in the tank, but there is a screen before the pump. It's possible that screen may have a deposit that's restricting fuel flow to the pump. It's also possible the pump's seals have been damaged and your fuel pressure is low.
 
Fuel pressure should be 43-56 psi and regulated to 47 psi. You'll need to lift to tank and adapt in a gauge between the fuel line in the tank and the fuel rail. You might have to pull the pump from the tank and inspect the screen

[ralph]

Behind the right alloy trim that goes down towards the foot rest is the plug for the 02 sensor
if you cant see or hear a air vac leak try disconnecting that, this then forces the ecu to run
safe settings for the mixture if the bike then runs ok it could be the 02 sensor, have you
checked the engine temp readout is that working as expected, if the ecu thinks the engine
is running hotter or colder than it is it will inject the wrong mixture,
Take it you have checked no beast's have made a home in the air filter.

[norcal616]

What gear are you in when the problem occurs? Like 6th gear doing 25mph?
 
I'm hoping you can provide a short video of the problem...

[ralph]

What gear are you in when the problem occurs? Like 6th gear doing 25mph? 
 

Surly not, then again someone did complain that after more or less every go faster mode in the book it would pink if held wide open up hill at 30 mph so you never know.

 

[rick]

he did say he's ridden another fz7 and that one did not do what he's experiencing.

[cc]

What gear are you in when the problem occurs? Like 6th gear doing 25mph? 
I'm hoping you can provide a short video of the problem...

It happens in every gear, but I can avoid 2-3000 RPMs unless I'm starting from a stop in 1st. I will try to make a video.

[cc]

Hmm, that changes my mind. 
Did it sit with gasoline in the tank for that year? In some respects, it would have been better if the tank stayed filled than if the gasoline was allowed to evaporate. Fuel residues are hard to clean these days. Just adding a fuel additive, like Sorkyah mentioned, may not be enough.
 
Sounds like the injectors were cleaned properly, so they should be OK.
 
There's no fuel filter in the tank, but there is a screen before the pump. It's possible that screen may have a deposit that's restricting fuel flow to the pump. It's also possible the pump's seals have been damaged and your fuel pressure is low.
 
Fuel pressure should be 43-56 psi and regulated to 47 psi. You'll need to lift to tank and adapt in a gauge between the fuel line in the tank and the fuel rail. You might have to pull the pump from the tank and inspect the screen

Yeah, I'll try the fuel pump and screen next along with the o2 sensor. Thanks!

[rick]

So it's ok beyond 3k RPM? That sorta suggests the O2 sensor

[cc]

So it's ok beyond 3k RPM? That sorta suggests the O2 sensor

 
Thanks everyone! Unplugged the o2 sensor and now it runs fine. Much appreciated.

[Beemer]

So what now? Does that sensor need to be replaced or can he go on riding without it or a fuel controller?

[rick]

This motor runs so lean in "eco" mode aka, closed loop FI, I suspect the worst that will happen - assuming it does not kick up an error code effecting something, and I would have guessed it should - is that fuel economy will suffer some as it now runs richer. As to how much, well that depends on riding style and how much time was spent with the FI in closed loop.
 
Dunno for sure or what the ramifications, but the part of the ECU's map that "learns" - the long-term fuel trim - has to be affected by disconnecting the O2 sensor.
 
It wouldn't pass an emissions test - if one was needed - that's for certain.
 
 
 
 

[sorkyah]

02 sensor shouldnt be too difficult to get a replacement.
yamaha part number 1WS‑8592A‑00‑00
Cant find out which sensor it is exactly
But o2 sensors come in a few flavors, there should be one available in your area in taiwan.

[rick]

After getting used to relatively inexpensive parts pricing for this bike, $125 for an O2 sensor seems kinda steep to me.
 
If it has 4 wires, it'll be self-heating. Might be able to find a Bosch version that'll work for half that price.

[sorkyah]

After getting used to relatively inexpensive parts pricing for this bike, $125 for an O2 sensor seems kinda steep to me.  
If it has 4 wires, it'll be self-heating. Might be able to find a Bosch version that'll work for half that price.

Problem would be making sure the wires are correct

[ralph]

I ran mine as a test for about a week with no problems, though it did seem use a little more fuel
which is what you would expect as removing the plug should force the ecu into running safe as in richer
settings, you can also get emulators but I have not tried one.
 
http://www.ebay.co.uk/itm/Oxygen-lambda-o2-sensor-eliminator-Complete-kit-Yamaha-MT-07-/261825655578
 
 
Take it the warranty as run out we get two years in the UK, if not they should fix it.
 
I would look on line if you want a replacement Yamaha is likely to be the most expensive option.
 

[rick]

After getting used to relatively inexpensive parts pricing for this bike, $125 for an O2 sensor seems kinda steep to me.  
If it has 4 wires, it'll be self-heating. Might be able to find a Bosch version that'll work for half that price.

Problem would be making sure the wires are correct

One side will be voltage in to work the heating element. The other side will be a voltage output for the ECU to see. That might not be all that hard to suss out. 

[Beemer]

This motor runs so lean in "eco" mode aka, closed loop FI, I suspect the worst that will happen - assuming it does not kick up an error code effecting something, and I would have guessed it should - is that fuel economy will suffer some as it now runs richer. As to how much, well that depends on riding style and how much time was spent with the FI in closed loop.  
Dunno for sure or what the ramifications, but the part of the ECU's map that "learns" - the long-term fuel trim - has to be affected by disconnecting the O2 sensor.
 
It wouldn't pass an emissions test - if one was needed - that's for certain.
 
 
 

I wonder if running it without will also affect the factory warranty or hurt the bike in the long run, slowly and adversely affect it's performance. So slow one might not notice the change??? 

[cc]

Hi all,
I plan on replacing the O2 sensor. Not sure if there are any adverse side effects, but don't really want to risk it.
 
I rode it today to work and found that the problem is actually only 95% fixed. The problem still exists in the same RPM range (2000-3000) under light throttle but it is just the slightest bit of hesitation now and avoidable if I just give it more gas. There's a motorcycle rental shop nearby that rents FZ07s so I might go rent one for a couple of hours today and make sure that it's not just something that happens at very low throttle/RPMs. 
 
Another question: If you are just idling along in 1st gear, is the bike jerky on occasion?