Misfire when rolling on the throttle.

[peteski]

Hi all, I’ve been a long time member, since 2003 when I bought the Fazer, but just haven’t kept up to date with the forum. The old bike is getting long in the tooth although I do pamper it. It see’s little use now I've stopped commuting out of London, maybe 500-1000 miles a year. Anyway, it seems to have developed a misfire. At certain throttle positions the engine hesitates and loses power. The best way to describe it, or bring it on, is to be in top gear part throttle holding a constant speed (the bike is running fine at this point) then slowly open the throttle. The engine bogs down and doesn't pick up speed. Things to point out:
-          The plugs are a few years old but haven’t seen many miles, maybe a thousand or so.
-          Plug caps replaced not so long ago.
-          The TPS failed last year and was replaced with a used part. Tests ok though.
-          Fuel filter changed (problem was there before also)
-          K&N fitted many years ago. Looks clean and not due to be cleaned.
-          Full stainless exhaust system fitted recently (can’t remember the problem being there before this)
-          Checked carb heater pipes for blockages. Seem clear.
It’s making the bike unenjoyable to ride. I did have a similar problem back in 2010 although that was only at idle/low throttle. It turned out to be a single blocked pilot jet and is not the same as what I’m seeing now. Other than stripping the carbs (which I plan on doing this weekend), has anyone come across a similar problem?

[clayt74]

Check that ya downpipes have the small Link pipes between 1&2, 3&4?

[rhinoeli]

Had similar symptoms. Bike lost power at a certain rpm (around 6000). One jet was blocked. A good carb-cleaning did the job for me.

[bandit]

peteski you say you fitted a stainless exhaust, fitting new downpipes will need you to have the carbs balanced you didn't mention you had this done my bike had these similar symptoms which when done cured it. 

[Gnasher]

Had similar symptoms. Bike lost power at a certain rpm (around 6000). One jet was blocked. A good carb-cleaning did the job for me.

 

If the bike is used very infrequently it's very likely one or more of your jets are indeed blocked.

[Deefer666]

 

FOR GOD SAKE RIDE THE DAMN THING!!!! 

[fazersharp]

Had similar symptoms. Bike lost power at a certain rpm (around 6000). One jet was blocked. A good carb-cleaning did the job for me.

 

If the bike is used very infrequently it's very likely one or more of your jets are indeed blocked.

Why would low use lead to blocked jets ---- is it to do with old fuel varnishing.
My bike has low use and I always make sure it has fresh fuel by coming back home needing a fill up so that when I ride next I first have to put some petrol in but only enough for the ride am about to do so it dosnt sit around with the old fuel from last time.

[peteski]

Good to see you’re still on here Gnasher.
My new headers do not have the link pipes.
The carbs were balanced after the exhaust was replaced. I balance the carbs once a year anyway.
It does get used, normally once a week, but it can sit for long periods from time to time. I’m leaning towards jets at the moment. We have a sonicator here at work which cleaned a completely blocked pilot jet last time around. I might just take them all out this time and run them through the machine.

[fazersharp]

PETESKI

An unrelated question for you about your avatar picture, I recognize it as a simpsons type drawing but I dont recognize the caractor -- who is it

[peteski]

It's me!

[fazersharp]

Thats what I thought ----------- That is so cool, I WANT ONE

[Gnasher]

Had similar symptoms. Bike lost power at a certain rpm (around 6000). One jet was blocked. A good carb-cleaning did the job for me.

 

If the bike is used very infrequently it's very likely one or more of your jets are indeed blocked.

Why would low use lead to blocked jets ---- is it to do with old fuel varnishing.
My bike has low use and I always make sure it has fresh fuel by coming back home needing a fill up so that when I ride next I first have to put some petrol in but only enough for the ride am about to do so it dosnt sit around with the old fuel from last time.

In my opinion fuel varnishing blocking jets is a bit of a myth, when varnishing happens and it's in the extreme it leaves a layer i.e. a varnish coating it doesn't block.  What can and does happen is the thin layer is disturbed and this then can block a jet.

What I've seen is more to do with rust and contamination particles from the tank, fuel lines, old fuel cans, pipes or garages which tends to be worse on bikes that are not used often.  The fact fuel isn't flowing or being used allows all these particles once in the tank to sink and form a layer, you then ride the bike the layer is disturbed and the fine particles are drawn into the carbs.  And yep they blocks the jets.     

The fault is often the tank it's self or fuel lines/filters then check the fuel your putting in.  Another myth in my opinion is fuel going stale I've had many bikes over the years, with more than one at a time to one/s I wasn't using that have stood all winter, even a couple of years with the odd run up every couple months and they've fired up and run with no problems.             

[Gnasher]

Good to see you’re still on here Gnasher.

I'm still about mate 

We have a sonicator here at work which cleaned a completely blocked pilot jet last time around. I might just take them all out this time and run them through the machine.

It's usaly the pilot jet/s or the air bleed channel in the carb body that block, you can also just get main jet as well or in stean of.  The sonicator will sort them all out if it's big enough to take the whole carb body, unblocking is only half the battle you need to sort out why! 

[sinto]

FOR GOD SAKE RIDE THE DAMN THING!!!! 

+1
(can't do the rolling eyes on my phone though!)

[peteski]

Update - Carbs stripped down and cleaned last week, all passages blown through, diagrams are all intact and jets clear. The sun had gone down when I'd finished so I took it up the road and back to see if it had made any difference. At low revs it was only running on three cylinders and almost stalled pulling away. Disheartened, it when back in the garage and I headed inside. The next night after work I started it and felt the temperature of each header, all were getting hot and this time sounded just fine. Took it out for a longer run to the petrol station to fill up and it ran smoothly. I can't say if the problem is gone or not as it used to come and go, some days worse than others. Time will tell I guess.

[peteski]

Another update - Dead happy. Went for a longer run last night and the problem has well and truly gone. It pulls well from low down in the rev range without hesitation and feels like a 600 again rather than a badly set up 350. Looks like I'll be keeping her for a little while longer then, my eyes always start to wander to newer bikes when this kind of thing happens. The MT09 still looks sweet.

[Gnasher]

Well done, get her out and enjoy.