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Author Topic: Misfire  (Read 886 times)

Cloud

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Misfire
« on: October 27, 2017, 08:44:09 PM »


Someone hit my bike with a car.
I've mended most of the broken bits, but it was on its side in the rain for a while, and has developed a misfire.

  • Misfires all through rev range, but most noticeable at 3k - 4k RPM
  • Is getting worse as the days go by
  • RPM meter on the dashboard drops when it happens
  • Only misses one or two ignitions at a time
  • Recent (two months) new battery
  • Still works mostly fine

Easiest suggestions first. I of course have my own ideas, but I wanna thread them here.
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umop-ǝpisdn

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Re: Misfire
« Reply #1 on: October 28, 2017, 03:47:02 AM »

Sorry to hear about the crash. I hope the broken bits didn't extend to you.

As for the misfire, obviously I will see it as electrical, because that's my focus.

Pinched loom? Water in a connector? Maybe start by testing the boots and leads. Also test that the leads are still attached to the coils properly.
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Cloud

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Re: Misfire
« Reply #2 on: October 28, 2017, 10:58:37 PM »

Sorry to hear about the crash. I hope the broken bits didn't extend to you.

As for the misfire, obviously I will see it as electrical, because that's my focus.

Pinched loom? Water in a connector? Maybe start by testing the boots and leads. Also test that the leads are still attached to the coils properly.

I'm fine. I was 100 yards away at the time, being sick behind a bush. I saw the car that did it drive away, but didn't realise what had happened until I returned to the bike.

I'm certain it's electrical, if it were fuelling or plugs then the rev needle wouldn't drop out. Where does the rev counter actually count from? Does it read pulses off of a coil? If so, which coil? Or does it read off the rotor/stator pickup?
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umop-ǝpisdn

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Re: Misfire
« Reply #3 on: October 29, 2017, 04:09:17 AM »

Not sure, I would guess front coil though, for efficiency's sake. Shortest length of wire.

Good to hear that you were not hurt and also that you found a bush to be sick behind.
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vulcan BR

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Re: Misfire
« Reply #4 on: October 31, 2017, 02:34:32 AM »

may be side stand sensor with problem, get ressonance by engine revs and fail.
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umop-ǝpisdn

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Re: Misfire
« Reply #5 on: October 31, 2017, 04:55:33 AM »

Definitely worth checking. The sidestand sensor is notoriously poor on the 650s at least.
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albertinhouston

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Re: Misfire
« Reply #6 on: October 31, 2017, 06:44:06 PM »

My process would be.... electrically.
1) Check to see if you have water in the plug hole(It would be worded differently if it was in the SLIH section of the forums).
     650s have a small port on each head for water to drain. If the 125's have them, see if it's blocked some how.
2) Determine where the issue is. front or back
     - spray water on the exhaust. In a normal condition it should bead of instantly. The pipe will stay wet if there is an issue.
       now we've established a focus point.
3)  Check plug wire connections. Mostly on the cap side
4)  250 cdi are known to fail. but since it was just bine before most likely not the problem. BUT when it's running bad give the cdi box a squeeze (top to  bottom). Typically the solder joint breaks on the board inside and that is the reason for failure.

where was your bike hit? back left side is the only place I can think of that a pinched wire could occur.  maybe the head light area....
mos everything else is protected inside of the frame
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Cloud

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Re: Misfire
« Reply #7 on: October 31, 2017, 11:46:17 PM »


It's not the SSSS because that's been disconnected and bypassed way back up into the loom. I couldn't add one even if I wanted to.

If it was a fault at the plug, then ignition would not happen, but the rev needle would stay steady, right? So it's likely to be a fault with either the coil itself, or the trigger pulses to the coil, which I think are sent by the TCI control box under the seat.

I think it might be vibration related, because the bike will idle almost flawlessly, but when I'm fanging it up some lanes and my keys are jangling around, it seems to happen a little more. But it's not predictable, because I came off some jumps yesterday and (broke the fairing) it seemed fine on take-off and landing, and was mainly dropping revs on the moderately smooth run home.

Yeah, it got shitmixed on the left-hand exhaust and went down on the right-hand side.

Other possibility - if the battery got damaged, would it cause the occasional single mis-fire?
« Last Edit: October 31, 2017, 11:48:19 PM by Cloud »
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vulcan BR

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Re: Misfire
« Reply #8 on: November 01, 2017, 02:58:12 AM »

battery fault? no. the bike generate power by engine. do you see some light blinking? may be short circuited some place that got hit by the car.

what about fuse box?
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albertinhouston

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Re: Misfire
« Reply #9 on: November 01, 2017, 03:24:07 AM »

 "If" there was water n the plug hole... Its not that the plug is misfiring... But its firing out the motor.  Basically the water is stealing the spark befor the plug gets it.

 Any chance you can get it to happen when the bike is parked?  This way u can eliminate some possibilities. Right now were still look at the whole bike.
Is it front
Is it back
Do both cut out...

Battery naaaa. Battery connections... Possibility

I have seen plenty of play with ignitions... Maybe bypass it with a bridge at the connection. To see if it happens or not.




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