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Flames, but no action...

2K views 11 replies 5 participants last post by  Demonic 
#1 ·
Okay, so my bike let me down, for the first time since I bought it so many years ago. Went out to the garage this morning, turned the key, , pulled the choke, pressed the button, and it started. Sort of. My revs went up to where they are expected, but then fall down to 1000, before going back up. Sometimes when the revs fall, the bike backfires, a bit of flames come out of the exhaust, and the revs go back up. This happens repeatedly. Sometimes the revs die, it backfires, and the bike dies.

I've uploaded a wee video of it in action. I am not touching the throttle at all, this is all my bike's demons in action:

https://www.youtube.com/watch?v=rfWGnDxZOrI

As much as flames coming out of the exhaust is deeply awesome, my bike not working isn't.


Any ideas where I start looking? The only thing I thought to do was wiggle the HT leads. They seem fine.

EDIT: Once it's dark out, I am going to try to video the flames. There's not a lot of flames, just a puff of blue fire when it backfires. Cooool....
 
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#3 ·
I was under the impression that if your coil was dying/dead, then your bike would have a hard time starting altogether, not start and go up and down in revs like mine's doing?
 
#4 ·
It does sound like it's an electrical problem and when my coil went it was intermittent a bit like your getting.

It could be a bad connection somewhere in the ignition system.

Has the bike been washed or is it wet? Water in the spark plug caps or connectors could cause it.
 
#5 ·
UPDATE:

I've been out to the garage, and checked my plugs. The left is lovely, the right is black. So seems I have an issue with my right hand carb. I replaced the offensive plug, and the bike started and idled no problem. I guess the spark plug was being a little ****e...

http://i.imgur.com/QUW4npU.jpg[
 
#6 ·
You got there ahead of me. Logically you were getting a spark so either the CDI unit was going South or you had a whiskered plug with a hairline crack that periodically earthed out. Or a sidestand switch jiggling on and off with vibration etc! Is it the black bonnie I have occasionally seen in Comely Bank?
 
#7 ·
Yup, that's me! The only other Bonnie I've seen around was one that had been nicked driving around Pilton with three scrotes on the back. That wasn't yours, was it?

I will keep an eye on that right hand plug. If it starts fouling again, I will consider replacing parts. I'm on a tight budget, so if I just have to keep replacing plugs every three or four months, it will add up! :)
 
#8 ·
When my coil went south, it was like someone was playing with a light switch - on one cylinder only.
...and a 400cc single, driving a 400cc dead cylinder, driving a 450lb beast with me on it - It wasn't going very far.

If you loose one cylinder at a time, it is the coil.
If both go, it could be the coil, sensor or ignition unit. That one is harder to figure out

of course, it could be a bad plug
 
#11 ·
I would suspect you just have a duff plug but the cheapest place I found for a new PVL coil at £46.80 was Motobins who are BMW parts specialists. See https://www.motobins.co.uk/library/70506.jpg and https://www.motobins.co.uk/mobile/b...&P=1&model=R Series 2 valve Twin&M1=4&M2=2610
You will occasionally see my black/white 2005 T100 in your neck of the woods. The PVL coil certainly runs a little sweeter than the Gill unit even when the latter was nominally OK. I am waiting for the leaves to clear a bit before venturing too far as I am South of you near Biggar and the side roads are lethal!
 
#12 ·
Right, bit of an update. I haven't changed the coil yet, due to lack of funds. But I took the bike out for a spin this afternoon, did the trick where you ride, kill the engine and coast to a stop, and check the plugs. My left plug is a lovely milk chocolate colour, my right one was WHITE. Remember, this is the brand new plug I put in to replace the one that was charcoal black! What the hell is going on?

Then I figured it out. The replacement plug is a NGK DPR9EA-9, not a DPR8AE-9! Bugger. So I suppose that's why it's clearly running hot. I will replace it as soon as I can! I am not doing damage if I ride my bike tomorrow, am I?
 
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