Strange Issue in the Rain

[mrhedges]

I went out to run and errand last week and took the motorcycle. 1981 gs850G. On the way back I got caught in a torrential down pour. I'm on the interstate and once I get closer to my house I decide to get off the highway for safeties sake. I taking city streets back to my place and the bike keeps dying at every stop light. I have to keep reving the engine to keep it from dying. I pull over and put the petcock in reserve thinking I'm low on fuel (my gas gauge stopped working a while ago) but that doesn't fix the situation and I can see gas flowing through my filter so the engine is getting fuel. Not wanting to try to attempt a fix in the rain and being pretty close to my house I make sure to keep the revs up at stop lights and get it home and I figure it might be clogged idle jets. I should also add it would only restart with choke.

Once the rain stops I go out to the bike and it starts up right away and idles correctly without dying.

Anyway the bikes at my buddies shop, we put new tires on it and checked the valves (this was a bit overdue) and two of the four exhaust valves were outta spec so I'm waiting on new shims right now

I'm still stumped why the bike ran so different in the rain, is water getting into the tank? or airbox?

[fbody_mike]

I was going to say you probably got water into your spark plug caps, but my experience is that this causes problems in the higher rpms vs lower, but it can be something to check. How old are they, how is the rubber?
Motors can suck in quite a bit of water and run. You can probably reproduce the issue with a good wash, I've found bad ignition coils that would only arc to ground when there was enough moisture in the air, like from the steamy wet engine in the rain.

[Agemax]

water in the electrics sounds more plausible. maybe the water is causing a connection to arc out somewhere causing a weak spark or low voltage to the system?

[rphillips]

If I wash my "98" Bandit 1200 at the pressure car wash, one cyl. will be dead till I ride a few miles. I'm sure it's the water on a plug wire, but it's never caused a problem, eventually, after the water dries off, it kicks in & is good to go.

[Tom R]

Contact breaker cover gasket?

[Brendan W]

Water on the HT leads is the most likely i would say. After dark you can see them arcing out sometimes.
This is what WD-40 was invented for. Spray the leads every once in a while and keep them free of dirt, it hangs on to water longer.

[LAB3]

A little silicone grease on the outside of the wires before reinserting them into the boots does wonders.

[dorkburger]

I had bad rubber spark plug cap seals - the ones on the end of the cap that seals the cap / plug.
Very predictably my bike ran like garbage after a wash or sitting in the rain. After the engine warmed and evaporated the water, things were fine. I finally replaced them and cured it.

[rphillips]

Hey Dork, have you seen the spark plug caps on a Bandit 1200? Ain't nothing like on your 1150. Works the same but totally different, they even seal water away from the spark plug & spark plug hole.

[dorkburger]

I've seen those. Probably keeps the crud out as well.

[Rob S.]

Certain Harley mods include a rain "sock" to prevent water from entering the intake.

[rphillips]

Personally I never liked to see bikes wearing socks, one reason I never had a Harley.

[Rob S.]

I agree. The only proper Harley air cleaner is similar to this:
asset (2).jpg
BTW, the only proper Harley exhaust is identical to the one pictured above.

[fastbysuzuki]

Water ingress is the most likely thing, I notated that you have an inline fuel filter is this a new fitment as inline filters generally will not allow fuel to pass through enough for good running.

[mrhedges]

Water ingress is the most likely thing, I notated that you have an inline fuel filter is this a new fitment as inline filters generally will not allow fuel to pass through enough for good running.

I've always ran the bike with an inline aftermarket filter