My buddy has a 2010 Ultra Classic that he bought used. It has a strange issue that we can't explain. The bike runs real good but when it's idling in neutral and you pull the front brake lever the engine rpm drops just a little like it's lugging down and it idles just a little rough. It doesn't happen when you step on the rear brake pedal. I'm stumped and so is he? My first guess would be electrical, brake lights putting a drain on a weak stator or regulator but the lights don't dim. Even in the dark there is no perceptible difference in his lights when he applies the brakes. Any ideas?

 

Push the brake lever only, don't put hand on throttle at all just touch aluminum lever only. See if problems repeats doing it that way. I'm thinking when grabbing brake lever the throttle is being forced to a "lower" setting than it is untouched? Just a guess. YD

 

We tried that. No help. It’s almost like what happens to a car with a vacuum leak.

 

And yes, I know Harleys don’t have vacuum assist brakes.

 

Engine RPM shouldn't really drop but you will definitely see the vibration characteristics change from the engine/frame/front end when you do this. Are you certain you're just not watching the vibration change? You can really see it on rubber mount bikes if you watch the engine/forks/front wheel when you apply and let off the front brakes. You'll actually see it. It's more obvious in bikes that have built engines with some thump.

 

Loose brake light switch pushing against the idle cable, assuming it's got a carb.

 

Bike got ABS?

 

Ok, I probably misspoke. The rpm does not drop according to the tach. It sounds like it drops but what we’re really noticing is exactly what you describe. What causes that?

 

Yes it does.

 

Pull the ABS fuse and see if it still does it? (if there is one) While you don't seen the lights dim, the 3 phase charging system could increase load on the motor if the ABS was doing something.

I believe the 10s with ABS are part of a recall on brake fluid change. The systems have been known to have issues. Don't know it's the problem but the only connection I know between the front brake lever and the motor is the charging system.