Topic: Idles Rough and No Power After Being in Rain

[phelbin]

I have a 1978 CB750A that's having some trouble.  I've owned it about a year and it has some issues, but it's always been reliable mechanically.  But all of a sudden it idles pretty rough, kind of like it's misfiring.  And it has almost no power.  I'll get 10 feet off my driveway, and it sputters and has almost no power.  Then as soon as I close the throttle it just dies.

This started happening after I accidentally left it out in the rain overnight, and I know that can cause problems like this with these bikes.  This isn't the first time it's been rained on...I do live in Seattle.  But it's never been like this before.

My first thought was electrical.  I cleaned up all the electrical connections I could find, and the battery checked out just fine (it's pretty new).  Just after I got the bike, I had to replace the ignition.  So I made sure to check that out.  That didn't fix it.

When it's idling in neutral there's quite a bit of white smoke coming from the exhaust, so I thought maybe water got in the bike from the rain.  I pulled off the airbox and it was totally dry, and the air filter looks good too.

I'm going to replace the spark plugs next.  I haven't done that in the year I've had it, so I figure it's due anyway.

Any ideas?


Thanks!!

[mystic_1]

The most likely culprit, I would think, would be the spark plug wires or caps.  Thats a pretty common cause of "runs bad after it's been rained on".

How long ago did it get rained on?  If the wind was bad as well you may have gotten some water pooled up down in the inner spark plug holes, or in the airspace in the center of the cylinder head (between the fins).  Got access to an airhose?  Blow compressed air into the head, between the fins between the exhaust flanges, and see if anything comes out.

Pretty easy to pull the caps off the plugs and give them a visual inspection.  You'll may find the rubber seals (one on the wire end of cap and one on the plug end) either dry and/or cracked and/or missing.

Couldn't hurt I suppose to also peek inside the headlight housing and make sure everything's dry in there.

mystic_1

[Vinhead1957]

Rain can get into the points too. Really poor gasket area.

[Bokeh]

If you look at page 10 there is one of the first strings that stated if the drain line is blocked water can collect under the gas tank lid causing water to get into the tank.  Worth a look.  You may want to check the drain tube and empty the tank and get some fresh gas in case. They also mentioned using seafoam to help clean out the carbs. 

Good Luck