When idling, voltage drops and engine starts to stutter/misfire

5 year old Motobatt battery.
Genny charges 14,5V at 2000 rpm.
Normal lights, no other voltage users.

Connectors all cleaned, checked and measured. Fuse box also checked.
Generator coils swapped 2 years ago, charging is -as said- okay.

When waiting a little longer at a traffic light battery Voltage drops to 11,0V and below (onboard V-meter)..
and engine starts to stotter/misfire.
When i turn off the light, it restores to 13,2V and engine runs fine.

Idling is set about 1100-1200 rpm..

Is the Motobatt the primary suspect or?

This happesn since about 3 months.
Before no problems at all...

 

Get engine hot. Then start bike on a car battery if you can to see if it idles without stuttering.

 

If i turn of the lights, Voltage increases to normal level and the stuttering stops.
This problem didn't occu in the years before with the same headlight.
Carging is 14,5V at 2000 rpm.

 

i would say the battery is on its way out, it should store enough power to keep the bike running whilst stood at idle for a few minutes, as you say , bike is charging fine whilst at 2000 rpm

 

Yes.. but.. it starts whithin 2 seconds.. At rest it has 12,7V.. Could the battery still be the suspect?
Otherwise... i'm out of options/theories

 

Battery is tested with a special device at a workshop, is okay.. Now i am really puzzled..

 

So how does the lighting wiring affect the ignition system? Yes lights will use power and below 2000 rpm it has ignition problems above alternator kicks in and it runs properly. Voltage drop issues below 2000 rpm. Resistance in light wiring connectors affecting ignition system. Lighting switch on handlebar? Corrosion can get under crimp connectors too.

 

A common issue with Yamaha XJ series motorcycles, where the ignition system malfunctions when the headlight is switched on, is often related to the starter relay or the starter button itself. Other potential causes include issues with the side stand switch, kill switch, or even a weak battery.


Troubleshooting Check the starter relay for proper function and voltage. A faulty relay might not be able to handle the additional load of the headlight and starter combined.

1. 
   
   
   • 2. Starter Button:
     [COLOR=var(--m3c10)]Inspect the starter button for corrosion or sticking. Cleaning the button and its connections with electronic spray cleaner and lubricating with silicone spray can help. [/COLOR]
   • 3. Side Stand Switch:
     [COLOR=var(--m3c10)]Ensure the side stand switch is functioning correctly and the plunger moves freely. A faulty side stand switch can prevent the starter from engaging, especially when the headlight is on. [/COLOR]
   • 4. Kill Switch:
     [COLOR=var(--m3c10)]Verify the kill switch on the handlebars is working properly. A corroded contact in the kill switch can cause similar issues. [/COLOR]
   • 5. Battery:
     [COLOR=var(--m3c10)]A weak battery might struggle to provide enough power for both the headlight and the starter. Consider testing the battery voltage and performing a voltage drop test while cranking the engine. [/COLOR]
   • 6. Wiring:
     [COLOR=var(--m3c10)]Check for any loose or corroded connections in the wiring harness, particularly around the headlight and starter relay area. A damaged or corroded fuse box can also cause problems. [/COLOR]
   • 7. Ignition Switch:
     [COLOR=var(--m3c10)]Inspect the ignition switch for any signs of damage or corrosion. It might need cleaning or replacement. [/COLOR]
   • 8. TCI (Transistor Controlled Ignition):
     [COLOR=var(--m3c10)]If the bike has a Black/White wire going to the TCI, verify the TCI is not being disabled by the safety circuit. [/COLOR]
   • 9. Ground Wires:
     [COLOR=var(--m3c10)]Check for a good ground wire connection from the fork to the frame in the headlight bucket. A faulty ground connection can cause various electrical issues. [/COLOR]

[/COLOR][/COLOR]

 

I found this don't know if it was posted by another member hope it helps.

 

Where is the on board meter connected

I am like the others and would have guessed battery based on most XJ's you hear of with a non functioning charging system can be ridden for a considerable time with a good battery before any performance issues.

That said, I also believe a well functioning charging system on the XJ at idle generates enough power to keep the battery voltage near its steady state of 12.6 volts.

Is the brake engaged during these low voltage events? The brake light double bulb uses about the same power as the head light.

What about ignition - have you verified proper resistance of ignition coils and caps, inspected connectors, and verified fuse and wiring condition for power to the ignition coils and TCI.

 

All contacts, switches and buttons are cleaned and checked. But i really, really do not understand how a start button or start relais, which are NOT in action when idling,

Maybe someone can explain?

New ground wire is installed, all ground contacts are good, battery is checked with special device.

Ofcourse, brake is NOT engaged when idling.

0-Ohm resistor caps, resistance free plugs, original coils.
Generator starts charging NOT at 1100 rpm but above that.
Generator coils have been replaced for good ones.

 

Is the on board meter connected to the battery?

On the 1982 Seca I have the AC Generator produces enough power that at idle the drain on the battery is near zero, not sure about the 1988

I can't even pull parts list on the 1988 since it wasn't sold state side, and Yambits seems useless. Does it have brushes? Has the regulator been replaced? Is there a FSM troubleshooting guide that you have followed to verify proper operation - for example all diodes good in rectifier, field coil voltage behaving normally?

Were the AC generator coils that were swapped verified to be defective, or was this just the shotgun approach?

 

No, old coils had wrong resistance.
At 2000 rpm charging at 14,5V.
So regulator works fine.
Idling without lights Volgate is 12,8-13,2V.
The rectifier (diodes) are in the regulator.. is it possible to check it with a multimeter?