Bike cuts out in the wet

[Ricco1]

I ride an old Yamaha 2 stroke. It runs fine but in heavy rain it cuts out. The solution is to spray wd40 into the spark plug cap, wait a couple of minutes, away it goes. I've replaced the cap and the ht lead but still have the problem.

Any ideas? It's a nuisance at best, or potentially dangerous.

[raesewell]

If WD40 cures the problem then you must have water ingress, double check everything and make sure the plug lead seal properly.

[Mississippi Bullfrog]

I bet there's a crack in the spark plug insulation. Once water gets in there it's shorting the plug out. I'd try replacing the plug.

[skyrider]

or the lead or maybe the cap

[megawatt]

Be careful spraying WD on sparks. I set my z1000 on fire doing that!!!

[Mississippi Bullfrog]

or the lead or maybe the cap

 

OP has replaced both the lead and the cap so unless the replacements are faulty it's more likely to be something else. A hairline crack in the spark plug insulation is difficult to see but if water gets in it the electric for the spark will track to earth.

[skyrider]

yes that will be the first thing to try then change the plug (what model is it)

[Stu]

fit a fenda extenda to try and reduce the amount of spray and also look for a better plug cap that can seal around the spark plug hole