1980 GS850 missfire

[Moarpower]

UPDATE. ISSUE HAS NOW THROUGH THE ENTIRE RANGE. DEFINITELY A SPARK ISSUE. Maybe the CDI is crapping out ? 1980 gs850g.
Vance and Hines 4to1 Dynojet stage 3.
Carbs all cleaned, running really well except right at the very top of the range.
It feels like it flat lines. Doesn't bog or pop like a rich or lean condition.
In neautral a quick rev will get it all the way to max rpm no worries. But under load she just seems to stop at the top end like it's cutting in and out for a split second.
Still very rideable but a strange problem.
We went up and down on the jet sizes all the way until it was bogging from the 150 main jet.

It's a strange one. Doesn't feel like a rich or lean bog. No surge when you roll back on the throttle, no pops or anything.

Could it be a timing thing ?

[Moarpower]

The issue worsens.
I have noticed that the battery is struggling.
It is a newer lifepo antigravity battery. There is an upgraded reg/rec on the bike but the factory cdi. I'm unsure as to if the ignition assembly has been upgraded or not along with the generator.

After the ride home the battery was completely dead. It wouldn't even turn over once.

Wonder if the charging issue or bad battery could cause poor running symptoms like this misfire.

Tested the volts at the battery at idle and only read 12.1.
Battery was fully charged last night and was dead after the ride so assuming the issue there.is the charging system rather than the battery itself?

[tom203]

It’s not cdi , it’s an ignitor. You need to sort out your charging issues…here’s an introduction

https://www.thegsresources.com/_forum/showthread.php?164993-Charging-System-QUICK-TEST

[Moarpower]

It’s not cdi , it’s an ignitor. You need to sort out your charging issues…here’s an introduction

https://www.thegsresources.com/_forum/showthread.php?164993-Charging-System-QUICK-TEST

Thanks mate. I'll get into that this weekend and run through the link you posted.
I'll worry about the charging first and go from there.

[Moarpower]

Ok so battery at 12.8v with key on, not cranking.

Idle is about the same. 13.2v at around 3000rpm. When I increase the revs higher it drops even lower, back down to 13.0v

[Moarpower]

Ok voltage up to around 13.8 max regardless of how high the revs are.
Tested the stator at approximately 4000rpm. 63, 63, 63, and one was a little higher at around 66.

[tom203]

I say classic connection issues.. remember step 5?

Step #5 by the voltage at 5000 RPM being higher than at 2500 RPM you have a pretty good indication that your connections are good. If the voltage at 5000 drops from 2500 you have bad connections. If you already checked the grounds then it is likely in the positive legs between R/R(+) and Battery (+) check fuse box and the large bullet.

note that the open circuit 63 to 63, etc test stuff is unloaded (except meter load) …when the stator is producing current,it’s subject to magnetic forces, wiggling things around.
I’d clean all the r/r and ground connections and hope for improvement.

[Moarpower]

I definitely feel like this is a connection issue. I replaced a battery and it rode well for 3 days without any trouble starting or stuttering.
Then it randomly misfires and rides fine again. I'll be going through the wiring and connections tonight and tomorrow

[Moarpower]

Here is a short video reading direct to battery. You can hear it is breaking up a bit and misfiring at this point. But voltage seems ok.

https://youtube.com/shorts/wzRI_z-InA0?si=tLFTppY2nptozv__

[Brendan W]

After the charging system connections are checked and cleaned go to the fusebox tail plug. Wiggle it and see if it produces a misfire and clean it anyway.
Check the fuses, particularly the glass ones can have high internal resistance where the internal solder is bad. Is one end of a fuse warm?
It seems there are a lot of poor quality glass fuses around.
Check the Voltage at the coil supply plugs, on the coil side of the plug with the plugs connected to the coils.
Compare with battery terminal voltage. Should be no more than a few tenths less. Ideally same as battery.
Open and clean the ignition switch, kill switch and the coil supply plugs. The coil plugs in particular can seem okay but hide a lot of corrosion.
I got back over a Volt at the coils just by cleaning these three. One coil plug was somehow giving an intermittent misfire that I could replicate by wiggling it.
Didn't need a new plug but had to extract the connecting pins and do a deep clean.

[Moarpower]

After the charging system connections are checked and cleaned go to the fusebox tail plug. Wiggle it and see if it produces a misfire and clean it anyway.
Check the fuses, particularly the glass ones can have high internal resistance where the internal solder is bad. Is one end of a fuse warm?
It seems there are a lot of poor quality glass fuses around.
Check the Voltage at the coil supply plugs, on the coil side of the plug with the plugs connected to the coils.
Compare with battery terminal voltage. Should be no more than a few tenths less. Ideally same as battery.
Open and clean the ignition switch, kill switch and the coil supply plugs. The coil plugs in particular can seem okay but hide a lot of corrosion.
I got back over a Volt at the coils just by cleaning these three. One coil plug was somehow giving an intermittent misfire that I could replicate by wiggling it.
Didn't need a new plug but had to extract the connecting pins and do a deep clean.

I should clarify. New coils on this with new leads. Fuze box has been replaced and it's currently using a moto gadget m-unit for relay circuit and switches. The charging and ignition circuits do not go through the updated unit. They are independent.

[Moarpower]

Cleaned connections and it rode beautifully for about an hour. It seems to get bad when it heats up.

[Moarpower]

I just did a little test holding one of the spark plugs caps just off the plug and the bike ran smooth. Seating the plug cap correctly and straight away back to misfire.

[Cipher]

I just did a little test holding one of the spark plugs caps just off the plug and the bike ran smooth. Seating the plug cap correctly and straight away back to misfire.

Replace caps........

[Moarpower]

Replace caps........

The caps are actually quite new. The leads are unfortunately fixed to the coils so I can't swap out the leads without swapping the coil.
I feel the issue may lie elsewhere in the ignition system tho. Are there any new ignitors that suit?

Pulled the plugs and they were jet black after an hours of riding. Swapped in new plugs, cut an inch off all the leads and reinstalled the caps. Ran a lot better but I'd be willing to bet the issue will return when I take it for a longer run tomorrow