Cutting out in the rain

[totty]

I've had other bikes misfire in the rain and fail to idle, but the symptoms were different today.

When the rain was heavy the bike ran as normal until I exceeded around 40 mph at which point there was some power loss and change of engine note, like one cylinder wasn't running. If I continued up to 60 it would then cut out completely and not restart until it had been left standing for a min. On restarting it would misfire at low revs for a while before running as normal.

In moderate rain the symptoms were more like typical wet electrics with poor running below 4k rpm, and very occasionally misfires above. Once the rain became light it ran as normal.
It was as if a quantity of water needed to be driven into somewhere to have an effect.

I thought I was going to need to call a breakdown service until I figured out how to ride around it and went through the towns and back roads on the way home.

It's fitted with a Boyer Micro Power kit (the one that includes coils), a foam air filter in the original airbox, but it's missing the airbox drain pipes and the parts below the airfilter - other than that it's standard. I've never ridden it in rain this heavy before.

Any suggestions?
Am I right to think it's electrical? There's lots of info online about waterproofing electrics, but what works for you?

[Bryanj]

I would still say a short at the leads/plug caps

[totty]

I can't see anything wrong with the leads or caps and couldn't see any arching. I still think you're probably right though, I might have to just replace them, but they're only two year old.

[LesterPiglet]

Did you try WD40 on them?

[totty]

No, I didn't have any with me. Is it of any use as a preventative?
I've read about packing caps and joints with silicone grease but I'd expect it to just melt out.

[matthewmosse]

Had a lot of this on both my 125's in the last 3 years, every time it was plug caps, though on the 500 the whole ht lead right back to the coil might be suspect due to age. I always found wd40 in the right place sorted it, though on the kh125 I sometimes needed to apply 2 or 3 times in 20 miles in extreme rain - a moto x plug cap in place of the old ngk thing sorted it. I added a small can of wd40 to the toolkit, lasts a very long time just used for this. After a while the residue seems to prevent re occorance of the problem if you are too lazy to replace the plug caps, spray grease might speed this up.

[LesterPiglet]

I wouldn't be without WD40 as a water dispersant. It works wonders.

[totty]

This morning I've removed the leads, cleaned and inspected them. The connections look sound at both ends, no corrosion - copper still shiny.
I found two very slight marks on the insulation where the leads had been rubbing on the frame so I've covered every bit of lead that touches the frame or anything else with a bit of fuel hose for extra insulation.
The whole lot has then been drowned in WD40, and I've ordered two little 50ml tins to fit under the seat somewhere.

I also found that the points cover gasket was out of shape and not sealing in some areas so I've siliconed the lip on the cover, just waiting for it to dry before refitting as I don't want to glue it on.

Is there anything else that's worth doing?
I could replace the caps but they're only 2 years and 1500 miles old.

[Green1]

I bet you sorted it if the points were getting wet that would definitely affect it.

Mick

[peterengland]

My 550 does not like the rain either. Friend of mine swears by throwing a bucket of water over the engine, if it stops you know you have something to resolve.

[totty]

Sounds like a worthwhile test, better than getting so wet you have to poor it out of your boots.