Hello gents, I have a 1988 FXRS Low rider which is giving me some grief. When riding it will accelerate up to 2000 RPM quite well but soon as It reaches the 2000 RPM it stumbles no matter how much you open the throttle. When I back off the throttle to below or anywhere under 2000 RPM it runs fine.
I have replaced spark plugs, ignition leads and the coil with no change. I also believe that the spark I get is nowhere big enough when shorting the ignition lead with the engine. There is no explanation in the workshop manual as to how to check the ignition module
Gratefully Ivan

 

Look at fuel delivery or even a vacuum leak. I would be surprised if it was an ignition issue.

 

mr. jack is right, check the fuel first. even if the module did not switch curves, it still would run way past 2k, probably to redline, just could cause heat issues under the right conditions.

 

I’m guessing a plugged up main jet. Let us all know what you find..

 

Today I took the carby out and pulled it to bits, blew every little orifice I could find with compressed air and could not find anything blocked or dirty. I still can not help thinking that my problem is the lack of a good blue ignition spark.
Any thoughts welcome.
Ivan

 

Spark is spark. Your not getting enough fuel.

 

Did you check the float level? Fuel petcock, fuel line. Has the bike been sitting, a little background would help.

 

Today I have checked for fuel flow from the tank by undoing the fuel delivery to the carby and had it going into a large cup. Looking at the flow I think the tank would empty in a matter if a few minutes. I took the bowl off the carby and found it pretty full as it should be.
If there was a vacuum leak it would be noticed mostly at the idle and not at higher rpm.

 

Maybe shorting at the switch or VOES maybe , elimination checks will find it man.
Maybe at the stage where it's stumbling see if the choke is by passing , or pull the choke on a little and see if it's better or worse.
It could be your timing plate now that I think of it too ,they sometimes act weird..
You need to nail down of it's fuel or electrics but you know this.
What carb ?
No matter what carb the float should be parrallel to the horizon/base when fuel starts to trickle out the needle and seat, check the seat it might be cactus.

 

...Unless the vacuum diaphragm had a leak. Check it!