VF500F Cuts Out at 8000 RPM

My brother, like myself, has a 1986 VF500F. It cuts out and runs choppy once you hit 8000 RPM. We have swapped all electrical parts from my bike to his and the problem still persists.

Before the problem started, his motor was pulled from the bike and rebuilt. I'm beginning to wonder if it could be a bad ground or wire as a result of pulling the motor. Does anyone have any ideas about what it could be? If my hunch is correct, what should I be looking at?

Thanks in advance for the suggestions.

 

Clogged main jets?

 

I failed to mention that we have also swapped out the carbs.

 

did you swap the cdi boxes? how about the coils? I don't really know other than maybe bad gas. Mine used to be really choppy until I cleaned out the main jets I know that, but if it was working it should now. you could try and put another ground on the engine or on the frame and see if that helps. extra grounds shouldn't hurt anything anyways. also make sure that you didn't pinch any wires when the engine was taken out or put back in. Hope this helps but it's cool that you got a pair of 500's in the family.

 

Sea foam?

Before you get to caught up in the wiring problem, is it stalling out from a fuel over/underload at the carbs? Or is it like hitting the kill-switch, and the whole thing dies all at once and smoothly? Is it stalling in nuetral when you rev. to 8K, or does this only happen under drive train load?
In any case, before you start ripping things apart, if you think it may be clogged jets, or out of synch carbs, try this:
When you want to eliminate a carb. problem without a rebuild, I would make certain:
1. synch the carbs.
2. run a can of Sea Foam through the tank (buy it at Carquest or google dealers). I put 3/4 of a can into a almost full tank of gas. Run the bike on center stand until hot, then let is sit overnight (I mean really let it sit for 10 hours). Then run it up to temperature, and wind the piss out of the throttle up and down the RPM's (may smoke, don't fret). Then it will be relatively clear of clogged jets, etc.
3. Put new plugs in, and run high-octane fuel.
4. Try 2 oz. of Marvel Mystery Oil in every tank of gas to maintain clean carb. life.
5. Re-check carb synch. It should not change, but blowing all the shit out may allow flows of air/fuel mixture to change at combustion.
6. Always 'Stablize-it' when storing
This will cost you a grand total of $25.00: plugs, sea foam, marvel...it worked well for me!