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I recently bought a 1986 VT500C. It is an awesome bike IMO, but it has one issue. I will describe the symptoms below:

1)Throttle response is good up to about 4-4.5k
2) At 4.5k to 5.5k the engines surges lightly. I can hold the throttle in place and it won't lose speed or bog down or anything, just surge back and forth. It feels like the engine is starved for gas
3)At 6k+, it runs smooth as glass up to the 9.5k redline.

The problem occurs in all gears, but is most noticeable at higher speeds.

Feel free to ask about anything I left out. Thanks for the help.

Sounds like a textbook case of needing the jet needle moved up a notch. Have you had your carbs apart yet?

Here's a decent post on carb tuning: http://www.atv-forum.com/general-atv-di ... guide.html