AceofSpades,
Here is a list of things that can cause high speed performance problems as well as bad gas mileage:
1. Low battery / charging system. A low battery will produce a low ignition voltage at the plugs which is most evident at higher RPM's and not all of the fuel will be burned.
2. Timing. Did you use a timing light to set the timing?
3. Stuck or no advance. When checking the timing with the timing light, did you check for maximum advance at 3,000 RPM.
4. Binding advance rod. Check out this video:
5. Fouled plugs. Did you install new plugs? Check them after you got it running?
6. Plug wire not making contact in the coil. Measure the resistance from plug cap to plug cap to ensure that both plug wires are making contact in the coil.
7. Brakes dragging.
8. N/A
9. Tire pressure. Pump up to 32 PSI for better gas mileage.
10. Drive chain too tight. That will rob you of power to the wheels and burn more gas.
11. Enricher plunger stuck partially on.
12. Enricher (choke) left on or partially on.
13. Weak or loose advance springs. Weak or loose advance springs cause the advance to use up some of the available movement because you have to essentially retard the advance to get it on the idle advance mark, so there is less movement available at higher RPM's resulting in poor power and gas mileage.
14. Timing chain needs adjustment.
15. Cheap or bad gas.
16. Low octane gas.
17. Water in the gas.
18. N/A
19. N/A
20. Try a run with a full tank of high octane, fresh, expensive gas.
21. Blocked fuel cap vent.
22. Incorrect sprockets. What RPM are you getting at 60 MPH.
23. Rear tire rubbing on brake rod or swing arm.
24. High wind resistance. Are you a large person?
25. Carbs not synced.
26. Blockage in the muffler(s)
27. Dirty or blocked air filters
28. High altitude
29. Very hot air, like 95+F
30. Very cold air, like 32F
31. Low oil
32. Really dirty oil
33. Gas in the oil
34. Weak TCI magnet in rotor. Unplug Reg/Rect to test