Idle drops significantly/bike stalls when stopping

Simcard

Simcard

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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
 
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.
 
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
 
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.
 
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.
 
Checked over my electrical system and found one broken wire and another loose wire going from stator to the rectifier. Soldered new connections and went for a ride. Made two or three accelerations to fast stop and the bike responded normally, going back to steady idle. Then abruptly it stalled out at the next stop sign. Decided to test the rectifier as a whole and was getting some weird readings so I ordered a new one thinking possibly the rectifier was bad. Installed the new rectifier and confirmed it is functioning correctly. Went for test ride and issue persists. Ran some tests and this is what I discovered.

1) At idle battery is reading 14.3-14.4 volts
2) Rev engine to 3,000 rpm and voltage stays the same drops to 14.3 volts
3) Turned on the headlight and voltage shot up to 14.8-14.9 volts
4) Revved engine multiple times with lights on and voltage dropped to 13.9 and then climbed to 14.6 and then fluctuated between 14.3 and 14.6 for 30 seconds or so and then bike stalled out.

Seems voltage is way too high at idle and revving, and then can't recover after engine is spun up and then returned to idle quickly. Something seems to be pulling a lot of power even when the lights are switched off. Any ideas where I might start looking to understand what is causing the heavy draw? Seems either an issue with charging, my Boyer ignition, battery, or regulator. Battery checks out as good but I can see about replacing it with a new battery I have and hopefully rule that out as a possible issue.
 
Simcard said:
I have a been using a VR-115 regulator. I have a spare Regitar USA regulator that I can try. Any other electronic regulators you recommend?
Click to expand...

I recognize the VR-115 regulator from here on the forum --- should work.

I am in Europe so here Other brands is used than available there I have used 3 pin Bosch or aftermarket clones .
They are not so expensive here as low as $ 15 sometimes .That means that instead of doing electrical fault finding
I get new regulator and rectifier are costing a few bucks but gets rid of that as the cause of the problem
I read that the rectifier is new

Having said that the fluctuation in Voltage you are reporting is something I Have never seen with a Electronic regulator
it is spot on ca 14.3 at 3000 rpm.

So either it is electric fault finding --- focus so the regulator gets correct system voltage --- as input --- If a voltage drop there the Regulator believes to low charging and increases. Noticed on the dash Voltage
or get another regulator and then do the electric fault finding if not solved.

If you give the Regitar type someone can tell if it is an alternative.

If you are good at electrics one can try to feed Regulator from battery with an inline fuse then the regulator have actual charging Voltage as input.
from Across battery. But be careful wrong polarity and the regulator fries
 
Its been a long time said:
If the rectifier has been bad, is there a possibility it has already damaged the VR-115?
Click to expand...

Yes I believe so

If it was me I would consider try to connect the VR- 115 across the battery as a test ( With a Fuse )
That way the regulator gets the actual ... on battery voltage and regulates that to the alternator .
If that give correct charging the wiring must be examined
If that don't give correct charging I would think again most likely new regulator as a first.
 
If I am reading this correctly, I can connect the positive side of the regulator (orange and brown wires) straight to the battery so it is reading off the battery and nothing else. Then start the bike and see what voltage I get at the battery at idle and at 3,000 rpm? If I put a fuse in the circuit, what size? 20amp? This is a bare bones layout of my wiring harness if that helps.
 

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I am not familiar with the VR_115 having 4 wires ---Stock and Bosch have 3
I don't know if they are connected but one of them are Upside 12 V that one goes to + battery
Please be careful so it is the correct one It looks as Brown is Switched 12 V

If you have a solid good ground
Otherwise a second wire black from regulator to - minus on battery

I would try a 10 A Inline Fuse if any

1782255755040.png
 
Charge the battery fully unplug the VR take it out and ride (mebby leave the headlight off)
Does that change your idle issue?

You are aware of early and late charging circuit brush differences?
Early
early charging diagram annotated.jpg
Late
latechargingdiagram.JPG
Early the VR controls +12 brush
Late the VR controls ground to the other brush.
You can't use a late circuit on early brushes unless you do the Nylon screw mod.
 

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