Timing, electrical, or carb issue?

[rlkarren]

I think I've run into this problem before because it seems familiar.. but I am not sure... It was discovered tonight while on a night ride and wondered if anyone could help and save me some time diagnosing the problem:

Bike runs great in with the key in the "day" position, but as soon as I turn it to "night", things go south. The following symptoms only occur with the lights on, (key in "night" position):

At idle it struggles to keep running, and frequently dies. While on the road, it does the same thing but it also has no power and acts as if it's flooding out. It will also occasionally miss and backfire. When I give it 3/4 to full throttle, most times it will clear out and run good until I back off the throttle again. If i switch to DC using the emergency switch it immediately clears up through the entire throttle range, same thing when switching between day and night position while standing still or riding. The problem also seems to get worse as the engine warms.

It seems the problem is isolated to the AC circuit but I keep thinking I need to recheck my timing, but if the timing was off, wouldn't that affect engine operation in the "day" position also? any other ideas?

I've eliminated the Voltage regulator as the problem and the coils tested OK. I checked and rechecked all electrical connections, and it also has new points and condenser. New battery. Carb has standard jetting except the main is one size smaller, (#140), for 4000ft elevation.

Thanks

Roger

[Dale]

Sounds like either points or condenser to me. I did experience this exact symptom on a 94 Wombat and replacing the points and condenser did fix it. I replaced them both at the same time and never isolated the problem to one or the other... I have always suspected that it was the condenser.
Dale

[Bullfrog]

A "thought experiment" suggests that timing is certainly not the issue since changing the main switch position can't possibly change the timing.

The same "thought experiment" also suggests that nothing you can do with the main switch will change the jetting, so the carb is not in question here.

Finally, the "thought experiment" tells me to do a detailed electrical check on the main switch looking especially for changes in resistance when connected to the wires which provide for "grounding out" the ignition system when the main switch is turned off.
When OFF - resistance should be zero ohms ("grounds out" the ignition circuit)
When in "DAY" - resistance should be infinite (eliminates the "grounding out", allowing the ignition system to work)
When in "NIGHT" - resistance should be infinite (eliminates the "grounding out", allowing the ignition system to work)

What the heck, I'm so far out on the limb that I might as well make a prediction . . . I think you will find that you have quite high (but not infinite) resistance when in the night position (which would partially ground out the ignition and make it run bad)

On the other hand, Dale's advice has repeatedly been precisely, exactly, on the mark in the past. So, if you have doubts about taking those resistance readings . . . new points and condenser are virtually always a good idea whenever the ignition system is acting up.

Ed

[rlkarren]

well.. feeling a bit sheepish again! Took off the flywheel cover and notice the stator plate was loose when I spun the flywheel to get to the points. Inspected for damage, (luckily there was none), cleaned it up and tightened it back down and she's running great again.

Thanks for your input. Again, you lead me to the problem and it did indeed save me a lot of time

Roger

[Dale]

Roger, Glad that you found the source and that it was an easy fix. Even knowing what the problem was, it is hard for me to understand why it would run just fine until the lights are turned on. The important thing is that it is resolved.
Dale

[Bullfrog]

An additional "thought experiment" suggested two additional possibilities (given the new information)

1. Changes in electrical flow resulting from changes in switch position cause a change in magnetic flux lines of force resulting in movement of the stator plate. (An intentionally complex flim-flam explanation)
2. WHAAAAAAAT?

Ed

[Yamadaka]

If the problem had not cleared up my guess would of been to replace the FLUX CAPACITOR. Just a guess