Idle drops significantly/bike stalls when stopping

[Simcard]

Been chasing an issue with my '75 XS where when coming to a stop the idles drops to lower than 1k. Usually the bike then stalls. If it doesn't stall, or I blip the throttle to keep the revs up, the idle will slowly rise back up to where I have it set at around 1800 rpm (set high trying to compensate for the drop when stopping). Initially I thought it was a float height issue. So I adjusted them but accidentally went the wrong way and lowered the fuel level. Naturally issue persisted. Took carbs off again to double check float height and discovered my mistake. Floats are set to 24mm on either side and on both carbs. Took the bike out and issue is still there. Thought I might have a dirty pilot jet but seems odd that it idles fine just sitting if the jet is indeed dirty. Any ideas as to what I might be missing or could check next?

Carbs are stock. Carbs air/fuel mixture needle is set to half a turn out. Using Uni pod filters and inline fuel filters. Just ask if further information would be helpful.

Thanks

 

[Jim]

If you go to neutral before you stop, does it still drop?
Reason I ask is it sounds like maybe the clutch is dragging slightly.

 

[Simcard]

Hmm that could be it. I will have to check that out and get back to you. Thanks for the great suggestion. I have noticed it sometimes stalls when putting it into first gear for the first time before I go out on a ride which would follow if the clutch is indeed not fully disengaging.

 

[JJames]

Hey guy's, what's the rough spec for the bs38 idle mixture. Dragging clutch sounds likeley.

 

[dave_a]

Classic description of fuel level too high.
Try this:
Shift into neutral while moving. Let it come to idle. Hit the brakes hard. If it stalls its fuel level.

 

[virgis9]

double-check throttle cable slack and that the slides are returning cleanly-sometimes they hang slightly and then settle.
I’d start with mixture screw adjustment and a good air leak check-that’s where this kind of issue usually lives

 

[Simcard]

Finally had time to take the bike out and see about trying some of these possible solutions. Tried riding, shifting into neutral, and then stopping and seeing what happened. It came with mixed results. Sometimes fine, other times it would stall. For the hell of it I adjusted my clutch and made sure it was fully disengaging to eliminate that possibility.

Some observations I had. 1) Bike idles high and then comes down when I turn on the light switch (my switch turns on the taillight (LED), gauge lights (LED), and head light (incandescent). Is this normal since battery draw increases? 2) Bike was warm and I was letting it idle (with the light switch off) to charge the battery after starting and stoping the bike multiple times, when it coughed and almost stalled. Then 30 seconds later it coughed again and stalled all on its own. I am wondering if this is a carb/fuel delivery problem or possibly an electrical problem. Everything I do to the carbs doesn't seem to affect the issue. Lowered the float bowls to 22mm - issue persisted. Raised them to 24mm (is the spec I found in the carb guide) - issue remained unchanged. I have adjusted the mix air/fuel mix screws in and out and that doesn't seem to have any positive effect either.

 

[JJames]

Did we talk about charging system and battery health. Have you checked across the poles, ignition off, and while idling/reving? Also, a battery that shows a "good" voltage can fail under load.(lights)

 

[Simcard]

I am fairly confident the battery and charging system are good. I have a voltage reader on my dash and voltage never drops below 12v when bike is running. It usually fluctuates between 13 and 14 volts when running. I will check over my electrical system and make sure everything is functioning correctly.

 

[Wagner73]

...voltage never drops below 12v when bike is running. It usually fluctuates between 13 and 14 volts when running.

Should be 13V+ at idle and ~14 - 14.5V at 3000+ RPM.