KLR650 RPM Surging at Highway speeds

[zachsnacks]

Alright riddle me this - 1997 KLR 650, runs perfect except over 65 mph, then the RPM surge, I can not feel any change in the actual power, and the MPH climb in a consistent manner all the way to 80, but 65-80 mph the rpm bounces from 5000-9000 erratically.

I have changed the ignition coil , which I ordered from 3d assuming the first thing, leaking sparks over to the sensor.

I have looked for loose connections thinking maybe something was not grounding and causing it to jump, but everything is clear.

But now I am out of guesses.

[William1]

Carb. Slide diaphragm might have a puncture/tear.

[zachsnacks]

2 minutes ago, William1 said:

Carb. Slide diaphragm might have a puncture/tear.

Even without a change in power? If I dont look down I swear its a clean climb all the way up, if I watch the dash its 5000 then jumping from 5000-9000 like a jumping bean. 

 

[William1]

Just now, zachsnacks said:

Even without a change in power? If I dont look down I swear its a clean climb all the way up, if I watch the dash its 5000 then jumping from 5000-9000 like a jumping bean. 

 

OK.. .maybe we need some clarification. Does the engine speed (road speed) actually change or just the tach?

[zachsnacks]

No change in power - just rpm jumping. I swear its like electricity was leaking from the ignition coil and throwing off the tach because it was so erratic. MPH climbs no problem from 50 -60-70-80. I only noticed it because I glanced down . 

[William1]

Ah, very different. Tachs fluctuate from bad cable (cable driven), moisture/rust inside tach (little magnet in the cup) or a poor electrical connection (electronic tachs), a wire or plug vibrating.

[zachsnacks]

Late followup to this - it was the CDI box, checked resistance following the factory manual and found them with no resistance. Upgraded to a new cdi and it was fixed! 

 

Ironically though, the new one was cheap chinese crap, and failed after two months. On the hunt for an OEM one now! 

 

Thank you all for your help