No spark to upright cylinder when hot.

[YourOldNemesis]

Behaviour:
Running a bit rough
Tends to backfire when throttle blipped from idle, then pick up ok or stall
If throttle opened slowly then it's fine
If I run it with HT lead off front cylinder it behaves the same but much worse
If I run it with HT lead off the rear cylinder it behaves exactly the same

Oil temp (according to gauges) is 130 deg C.

Anyone have any advice on curing this problem, or how to investigate further?


Thanks

YON

[slob]

After inspecting the plugs for dirt/damage, first thing I'd try is HT leads. My Harley used to develop a misfire on the rear cylinder once the leads were a few years old.Try a cheap pair from a car accessory shop to eliminate the problem before spending serious money on 'genuine parts'(I don't know, maybe Ducati leads are just a few quid).

[crust]

- is the idle speed right? too low and it will cause problems

- carbs out of balance?

-air screw needs adjustment

[YourOldNemesis]

Sorry, should have mentioned it's a 620 ie, so no carbs to play with!

I followed the HT lead back to the coil that sits under the black plastic thing to the left of the saddle. Cos it's one of those new fangled jobbies, it looks to me like the HT lead and coil are a single unit. Can anyone else confirm that this is correct on the 620?

Either way I suspect that it is the overheating of the HT lead itself rather than the coil that causes a problem - cos the lead runs past the cooling fins of that head, but the coil is not too near anything hot.

Has anyone else experienced this problem? As I think the lead and the coil are a single unit, it's not possible to just use a lower resistance lead, does anyone else have another solution? - eg. re-routing the lead...


Having slept on this, and still being irritated I think it is worth pointing out that this is utter sh*te. When it's wet, the front cylinder misfires because the plug gets wet, when it's dry and warm the rear cylinder backfires into the airbox becase the HT lead gets to hot.
I don't remember anyone mentioning to me that I would only be able to ride this bike when the weather is cool and dry - maybe that's why they have 2 cylinders - so that at least one always works.

[spacemonkey]

Have you tried wrapping insulating tape around the offending lead? Maybe it is shorting? Decent plug caps (could also be the rear's cause of grief..) and a smear of silicone grease on it's lip will keep water at bay. Just my £0.02

[Zimbo]

Hmmm i wouldn't discount the possibility of fuel delivery if I were you.
Blocked fuel filter? Blocked injector?

[slob]

s'pose you could always swap the coils over to see if you get a front misfire, they appear to be the same as each other on mine ('02)

[YourOldNemesis]

I've started by swapping the plugs over, but haven't had a chance to test yet. I need to then go for a hot run to get the engine up to 130 degrees so that I can test it (once it's hot it's pretty repeatable, but disappears all together when cold.) If swapping the plugs hasn't moved the problem (or eliminated it because the front one runs cooler), then I'll swap the coils over and try the whole thing again...

I can't see how it would be a fuelling issue because it only happens when really hot, I would expect a fuelling problem to happen all the time.


Thanks for you help


YON.