Gl1500IS Stalling/unsteady idle when warm and fan is running

[Memor86]

Hello folks, I rebuilt my carbs and bench synced them, set the pilot screws at the recommended turns here. I can't remember exactly but somewhat 2 and 1/4 or 1/2 turns out.

It runs great at apeed, at idle when cold it randomly pops on the exhaust, but the rpm does not jump up and down, besides the poping it sounds very smooth. No smoke or funny smells on the exhaust.

the bike is hot and is on idle speed it will have random hiccups but goes smooth again. When the fan kicks in, that hiccup makes the engine to stall. I have tried to compensate it by raising the idle speed to 1000 rpm but that's not the proper fix and it still makes the engine to stall but not so often.

Bike has 90kmiles stock exhaust non-california edition and gas k&n air filter with the black foam thing on it. (I have not cleaned it)

At speed runs great and powerful but the idling is annoying and sometimes stalls at the red lights. I guess the problem lies in the pilot screw setting.

Ps. I've checked the choke, it works fine and is not stuck.

Any suggestions??

[gordonv]

I'm not the best with carbs, but it sounds like a vacuum leak to me.

How about the intake tubs O-rings? Spray some product at the tub/engine, and listen for a change of rpm (WD40/ether/???)

[Firefighter]

Check battery voltage at battery and then at frame, could be bad frame ground. In other words, while it is acting up, use voltmeter on battery and find voltage then touch negative lead to frame and see if voltage is the same or not. My IS had same problem and I ended up running a jumper wire from battery negative to frame and it was cured. Ignition grounds through the frame, but battery ground wire attaches to the engine.

[WintrSol]

Just FYI, the coil on the left frame tube, under the tank, has a harness ground wire connected to it, and one of the holes the coil bracket bolts go through is cleaned of paint, so the coil bracket makes that ground go to the frame. I don't know about the other coils, but, whenever I open a connection like this, I clean the bracket and frame contact areas with a soft brush and contact cleaner, just to make sure I have good grounds. If it is a ground issue, that would be a good place to check.

[Ricky-D]

Sounds like the carburetor synchronization is the culprit.  That's my first choice.

***

[WintrSol]

Yeah, start with the carbs; more likely than grounds, and easier, IMO, to sort out.

[Earl43P]

Humor me...

Connect a set of jumper cables to the Valk battery and your car (don't start your car, just connect it).

Run the bike until the fans come on. Result?

I think your alternator is the culprit, not carbs!
Specifically, I think the brushes are worn and low rpm fails to generate enough amps for spark AND fans.

[gordonv]

+1 Logical to me too.

Can also do the same with a meter too.

Might be like my alt was, brushes sticking in their settings. Wore away till there was no more contact (didn't move), and no more power. Removed, cleaned, and worked fine again. 30K miles left (estimated) on the brushes.