R80st- low speed misfire/cutout after rain

[ampthill]

Took my r80st for a ride round the local lanes yesterday. Got caught out in some sharp rain showers. Up until then bike was running fine but soon developed a misfire from one of the cylinders. Would just about run on both cylinders if revs kept above 3000, but any less than that and would go onto 1 cylinder. Would occasionally restart firing on both cylinders, which can be interesting when banked over on a wet roundabout...

Have let the bike completely dry out overnight but problem still seems to be there today. It will start and run but goes onto 1 cylinder if revs drop and will then die on one of the cylinders ?right unless revved. Checked leads and spark cap and they are both fitted correctly.

I was thinking it maybe a coil but thought I'd try the wisdom of the forum before going any further. Any thoughts most welcomed.

Peter

 

[Bubb]

wet leading to misfire suggests coil or HT leads..... my bet would be the HT leads are breaking down.

How old are the HT leads?
Does your ST have the little plastic flap on the frame at the front to protect the coil from the wet....
it should be just by the horn on the cross piece at the top of the tubes running down from the headstock....if this is missing, then water will be flung onto the coils.....

Best of luck..... I hate electrical problems !


Bubb

 

[peepingtom]

I had a similar thing happen on my R65. That turn out to be a cracked coil with water getting in . Luckily I coasted to a garage forecourt where a can of wd40 was purchased followed by a bit of tape to get me home the 150 miles. It did

 

[Mr K]

Check your carb float bowls.

 

[Beemerboff]

Happened to me on my four plug bike, and as each coil feeds both sides I think Mr K 's suggestion is worth a try !

 

[solidstate100]

its a wasted spark ignition system, so swap the HT leads over. Does the problem change sides? if yes then it is electrical, if no then it isnt electrical. if it isnt electrical its fueling (as Mr K says check your bowls), or possibly compression related.

Also, if the bike got a decent soaking it WONT have dried out properly overnight, especially if there is water ingress into componentry - I have pulled bikes apart after 2 weeks in a garage after rain and was still mopping up/chasing out water in those hard to reach places......

 

[Steptoe]

Took my r80st for a ride round the local lanes yesterday. Got caught out in some sharp rain showers. Up until then bike was running fine but soon developed a misfire from one of the cylinders. Would just about run on both cylinders if revs kept above 3000, but any less than that and would go onto 1 cylinder. Would occasionally restart firing on both cylinders, which can be interesting when banked over on a wet roundabout...

Have let the bike completely dry out overnight but problem still seems to be there today. It will start and run but goes onto 1 cylinder if revs drop and will then die on one of the cylinders ?right unless revved. Checked leads and spark cap and they are both fitted correctly.

I was thinking it maybe a coil but thought I'd try the wisdom of the forum before going any further. Any thoughts most welcomed.

Peter

Do you still have the original grey dual output coil fitted ? if so it's cracked.
Very common problem back in the day and why they changed the style of coils.
A K100 coil is a very cheap ultra reliable replacment option.

 

[ampthill]

Update:I had a very generous offer from 2gses who offered to lend me one of his spare coils to see if this cured the problem. Glad to report it did so, following the tip from 2gses, ordered a new one direct from my local Bosch agent and picked it up today. To note price for the new one little different to what BMW breakers wanted for a sh one

Peter