Poor Performance in the Rain

[whereshaldo]

I've got a problem with poor performance in the rain that I just cannot seem to puzzle out. Its a stock '81 C70. Whenever we have a good amount of rain the bike has a tendency to bog down and loose all power whatsoever. It will idle just fine, and in 1st gear I generally have no problems getting the bike up to full revs. As soon as I shift into second all momentum stops. Its almost like when Han tries to put the Falcon into hyperdrive. If I shift back to 1st i can regain the momentum, and if I let the bike scream in first it seems like I can eventually shift into 2nd and have power. Today was a little different in that I had a big hill to go up which generally requires 1st anyway, and i definitely didn't have all the power I needed.

Any thoughts? i do have the breather drain tube plugged up, so its not sucking water up that way. It also doesn't seem 100% electrical because turn signals and lights all continue to work just fine.

Thoughts? I've got 8 hours before I have to slog home.

 

[69ST]

Based on that info, it's inhaling water. Not familiar with this bike so bear with me...why would you plug a drain/breather? If you're talking about the airbox, airflow will follow the path of least resistance, i.e. the airfilter. If the airfilter element is not the path of least resistance...voila!...there's the problem.

 

[cjpayne]

I agree with Bob. That breather needs to drain. Your plug cap could also be not sealing around the plug and letting water in the cap. Drench the inside of the cap with wd40.

I would also get the bike level upright and drain the carb bowl just to see if there's some water in there too. I doubt it, but cant hurt to check.

 

[whereshaldo]

Sorry i don't mean breather, i mean the drain tube that comes off the airbox. Part 20 shown in this diagram.
https://www.tmsparts.com/media/oem/orig/HOM/1350/79347.gif

Do I even need all that crap? Seems like eliminating all of this would solve lots of potential issues.

My inclination is that its more spark plug related than airflow related. Either a leak on the seal around the points cover or around the plug cap. All of these parts are relatively new, so I'm not dealing with old cracked rubber. Air filter is new, airbox seals are all nice an pliant. I may just have to get a hose and start dousing areas and see what happens.

I should also mention that I just hopped on and took it to get lunch. No rain, but only 4 hours later. Not so much that everything was fully dried out but it should at least eliminate water in the fuel as an issue or a wet air filter.

h

 

[kirrbby]

There is probably a little drain hole in the bottom of the stator cover too, that could be allowing water in...fouling the points.
The ignition system is pretty much separate from the lighting. So even tho the lighting is working fine, the ignition coil, points, etc could be malfunctioning.
I'd look under that stator cover

 

[whereshaldo]

I just went and looked at things again. I think the stator cover is solid. Seal seems tight, and everything looks good there. I don't see any moisture inside.

Back edge of the fender is pretty munched up, so its possible there is more spray than there should be, but that seems to be asking too much of the situation.

The coil wire looks to be in good shape. its actually sheathed in an outer covering of rubber that is still in good shape. The one place I do see a potential issue is at the small rubber boot that seals the cap to the wire. Since the plug wire does exit out an up, I guess its possible that water is leaking down the wire into the joint where the cap screws into the plug wire. I may try to slip some adhesive lined heat shrink over the joint so that everything is glued up tight. Maybe i'll hose it down first and see if i can replicate the issue. The only other thing I see is that there are two similar tubes that exit the carb. One is the bowl drain tube and one is the float overflow tube. The float overflow tube is pretty long -- it hangs about 2 inches below the bike. Could this be sucking up water?

h

 

[69ST]

The weekend is almost upon us, then you can do some testing. If you really think that it's water causing misfire, get the motor partially warmed-up...then break out the pump spray bottle, filled with water and spritz the plug cap. If that triggers the symptoms, you'll have verified your suspicion. If not, I'd be looking for a way to duct dry air into the airbox. At this stage of the game, I doubt that it's an ignition problem, unless the points were getting damp. Otherwise, ignition tends to be all-or-nothing. If it was arcing, upstream of the plug electrodes, I'd expect misfiring...and uneven running at that...not loss of power. What you described sounds more like the incoming air + fuel charge being partially-doused by excessive moisture entering the combustion chamber. Water is incredibly efficient at heat absorption...and hindering combustion.

 

[whereshaldo]

Is the crankcase breather assembly necessary? I see this is a USA item only. With all these joints and odd little hoses, I can see how this would admit some water into the carb assembly. Any reason not to just remove all these bits?
Hal

 

[69ST]

Can't really advise you on this one, I don't deal with emission-era machinery. On my bikes, I run open-element air filters and the crankcase breather is open...save for the mushroom-style filter at the end of the hose. That's all the more emission pieces on my antediluvian (1972-earlier) bikes.

And I am a hardcore fair weather rider. Much below 70F, or if there's a chance of rain, I'll drive thankyouverymuch. The primary side effect is zero experience with wet weather operation. I still think you ought to begin with the spray bottle testing first.

 

[whereshaldo]

Well I wish I had something incredibly revealing to report but I could not find any one thing that was the culprit. I did re-seat the intake tube onto the throat of the carb. One thing I did notice that could be an issue is that it seems like the bottom of the airbox is melting off and separating from the sides -- this may be a result of my spraying starting fluid into the throttle at one point.

I did put in the Dr ATV long duration cam (I find its best to complicate things with multiple changes at once). Definitely a bit more higher end torque which is helpful, but also runs a bit lumpier.

H