cb750 power is wonky after the rain

[rachsrib]

Have a 78 cb750 that ran great last month but like most of the US my city has been getting hammered by rain this month.

Finally took the bike out 2 days ago and it would die shifting into first from idle and into 1st from 2nd, but I was able to pull in the clutch and restart the bike while riding. And when I say die, there was no sputtering, just black all of the sudden.

Today on my ride to work she decided to run fine until I was about a mile from home and just died while in neutral at a stop light, no warning, just dead. I pulled over and was able to get it to restart a few times, it would rev for 1-3 seconds and then just dead, after15 minutes of this I couldn't get it back on the road and had to leave the bike.

I am guessing that this has to do with the recent rain and sitting for 3+ weeks. Fuses looked fine. When I turn the key the headlight comes on and if I jiggle and try enough the bike will fire up for a few seconds.

Not sure where to start on this one. Ignition switch? Kill switch? Points?

Thanks

 

[Tim]

Two things spring to mind. The cover on your points - is there a gasket and is it water tight. 2nd is what sort of air filters are you running? Pods or the box? And how much rain was your bike exposed to?

If your bike is sitting in a garage and it rains for a month and then you go for a ride, clearly nothing should happen. You don't mention just how wet your bike got, if you're riding in the rain or what.

 

[rachsrib]

Forgot to mention all that.

Stock airboxes, some of the rubber is rotted out and not a perfect seal. There is a gasket on the points cover. The bike sits outside under a tarp. But a few times, including last night the wind whips hard enough to pull it off.
The nights that I found the cover off, would have varied from very light drizzle to hard downpour (last night).

Haven't ridden at all in the rain, no fenders on this bike and a bad experience with rain riding in the past.

 

[diggerdanh]

Not sure if it helps or is even relevant but I had a 1999 blazer that I parked in the driveway. It was pretty dependable except for after heavy rains or just wet conditions for several days it would not start. Would just keep turning over but wouldn't fire. Condensation would build up in the distributor cap. I'd have to pull the cap, wipe down the inside and spray everything with WD-40, put everything back, and then it would start right up. I replaced the distributor cap and rotor and it helped for a while but eventually came back. It seems to be a common problem with GM cars of that era.

So based on my previous experience I would check for condensation building up somewhere that would affect electrics - coil, inside points covers, spark plug boots, etc.

 

[lil beast]

Wet wires, plug caps, coils could be shorting out, also check for water in the carb bowls. Run the bike at night and check for sparks along the wires wherever the wires touch anything metal.

Good luck

 

[irk miller]

I had an similar issue recently and it was in the headlight. The bucket wasn't well sealed and it caused a short in connector. It drained power from the battery causing things to run badly. Sounds like wet electrical, no doubt.

 

[rachsrib]

Thanks for the suggestions. I do know that there is a crack in the headlight so I think I will start there with some dielectric grease and work my way down.

Carb bowls might also be a good place to look as I know the box isn't perfectly sealed.

For the ignition, is it ok to shoot WD-40 down and run the key in and out a few times or is there a better option?