Right cylinder suddenly began to intermittently fire after riding in the rain

[sixfiftyone]

Thanks you in advance for helping me get my 79 XS650 Special back on the road again.

My bike was running great until yesterday. I was riding and got stuck in a downpour, bike was running fine for 20 or so miles, and suddenly my right cylinder started firing intermittently and then stopped firing altogether.

I let the bike sit and dry in the sun for a day figuring it could be an electrical issue. it started right up, both cylinders firing, but when revving the engine right cylinder backfires like crazy and dies out. When the Tachometer hits 4K both cylinders fire again. On idle both cylinders fire, but when I let the clutch out the right cylinder pops and stops firing.

Since my problem came about with the rain I thought it could be an electrical issue; the right side coil tested fine and I'm getting spark. Could timing be an issue?

Any ideas on what's wrong with my bike? It seems like if it was an electrical problem I wouldn't be getting spark at all. Do you guys think this could be a carb sync issue? I wonder if maybe I suddenly developed a vac leak around carbs somewhere.

 

[weekendrider]

Were your air filters sucking water?

 

[sixfiftyone]

I don't think so. Running stock filters that are covered. It was raining, but not so much that filters would have been sucking up water.

 

[Tomterrific]

Take off the points cover and spray with WD-40, then clean the points. Check that the gap has not closed up. Oil felt and a finger print of grease on the points cam in front of each point heel will extend life.

Pull the offending plug wire and check for continuity. Spray WD-40 inside the plug cap, on the wire and around the coil, then wipe clean.

If you think a drop of water got into the float bowls just drain the bowl through a paper towel. A good practice for old bikes anyhow, just to see if any debris is inside. A drop of water can block a main jet when the throttle is opened.

Tom

 

[sixfiftyone]

Thanks Tom. I'll check the points as soon as I am able.