Rough running in wet weather - why?

[full_chat]

I commute on a 2002 Fazer, in the last few weeks it's started misfiring when riding in heavy rain or after I've washed it.
I'm not mechanically minded so when I put the bike in for a service I reported the issue, however, the garage were open in that they didn't find any obvious issues and their next suggestion was to rebuild the carbs. Before I start fixing parts until the problem goes, does anyone have any ideas what the issue might be?

Thanks

[LiquidGnome]

I'm not particularly electrically minded, but it might be worth checking around the spark plugs, as a worn shroud on one of the high voltage sticks could cause issues. They might be a pain to get to though. Although I'd have thought a mechanic would have checked that.

[LiquidGnome]

LiquidGnome said:

I'm not particularly electrically minded, but it might be worth checking around the spark plugs, as a worn shroud on one of the high voltage sticks could cause issues. They might be a pain to get to though. Although I'd have thought a mechanic would have checked that.

That might all be complete nonsense, best wait for someone who knows what they are talking about.

[Biker 1]

My dad had a car a while back that did exactly this: eventually someone swapped out the HT leads & everything was fine. I'm guessing it would be hard to pick this up during a service, short of hosing down the bike during testing....

[anonymous-user]

full_chat said:

however, the garage were open in that they didn't find any obvious issues and their next suggestion was to rebuild the carbs.

I admire their utterly flawed logic!

Almost certainly something electrical, and almost certainly high tension so check coils, HTs, and all associated wiring.

[Lavs]

Had a similar problem on my XT1200z Super Tenere and had to replace the ignition coils as the rubbers had gone and was letting water on to the plugs

[Stig]

As above, check the coils for water ingress. The other thing that's a weak point on Yamahas are the HT leads. They have very thin insulation and if one sits near the engine/frame it can short against it. Had exactly this issue on my TDM.

New HT leads, self amalgamating tape around coil sockets and plug caps and problem disappeared.

[xeny]

full_chat said:

I commute on a 2002 Fazer, in the last few weeks it's started misfiring when riding in heavy rain or after I've washed it.
I'm not mechanically minded so when I put the bike in for a service I reported the issue, however, the garage were open in that they didn't find any obvious issues and their next suggestion was to rebuild the carbs. Before I start fixing parts until the problem goes, does anyone have any ideas what the issue might be?

Thanks

How thoroughly are you "washing" around the cylinder head area?

There's a rubber flap on these that goes down between the exhaust camshaft part of the cam cover and the spark plugs - is that still intact/in position?

[mister_ee]

There's a drain hole for the plug recesses on the left hand side of the cylinder head, if this gets blocked the plugs and caps sit in water

[Mr2Mike]

Also HT leads can degrade with age and become 'leaky'. My Blade had a very slight misfire that became much worse in humid conditions, changed the HT leads and all fixed.

[full_chat]

Thanks everyone. The leads look in good condition, but I'll check when they were last replaced and put some new ones on if not recently. I can see the drain holes, I'll poke something through them - no water resting there earlier but they must just be draining slowly.

The rubber flap is still in place in front of the leads and I'm washing the bike in the same way as I have for years. The other issue could be it hasn't been washed as often this winter thanks to young kids now being around, maybe some of the electrics have suffered languishing in winter crud. I'll check the Haynes manual and see if there's any obvious connections I can clean.

[Pothole]

I'd get a new place for repairs and advice, too. No way is that a carb issue.

[cmaguire]

If you're feeling brave and don't have a pacemaker you could give it a wash then when the symptoms occur run your finger over the HT leads and plug caps. If you get a belt you may well have found the problem

[Stig]

cmaguire said:

If you're feeling brave and don't have a pacemaker you could give it a wash then when the symptoms occur run your finger over the HT leads and plug caps. If you get a belt you may well have found the problem

Or rather safer - run it at night and see if you can see it arcing!

[full_chat]

In the freezing cold and with bleeding knuckles at the weekend I tested the leads, spark, coils etc and ended up by removing a very damp corroded 12v fag lighter that I forgot was there (installed about 5 years ago and used once whilst touring). It seemed to instantly run better after that, so looks like it's fixed. I should know for sure after tomorrow's heavy rain!

[moanthebairns]

Funny this has popped up I have a problem with my ninja spluttering around town, fine on full power and it instantly gets worse afterI jet wash it......

[EvoBarry]

These old Fazers are well known to have weak plug caps, they fail when they get too wet. Swap for NGK or similar and it should fix itself. I run an 02 Fazer btw, have done for seven years, 50k+ miles..

Check the drain holes on the sides of the head too, should be obvious (and clear).