Xs650 runs great but max speed 65mph

Bike goes slow (< 65MPH)

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.
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.
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. Speedo out of calibration. You are actually going faster than 60 MPH! Use your GPS to check the speedo.
9. Tire pressure. Pump up to 32 PSI for high speed.
10. Drive chain too tight. That will rob you of power to the rear wheel.
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.
14. Timing chain needs adjustment.
15. Cheap or bad gas.
16. Low octane gas.
17. Water in the gas.
18. Partially blocked pet cock or fuel filter.
19. Paper filter that has low flow when the tank is not full.
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. Throttle cable not fully opening the throttles.
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
35. Cracked carb boots.
36. Hole in carb diaphragm(s)
37. Cheap pods covering air hole in carb inlet
38. Clutch slipping
 
Holes in carb diaghram causing flutter at high rpms? Need bigger main jet? Just throwing it out there.
 
This is drastic but subtle at the same time, if that makes sense. I would check fuel delivery. Dump the gas from the tank and swish out the crud, remove and THOUROGHLY clean the petcock and clean/replace fuel hose and filter/s. Those are small passages in the petcocks that need to be as clear as they can be. The engine can not burn fuel that it doesn't get delivered to it. Maybe I'm full of shit.

Scott
 
Scott.... I had an engine that wasn't getting enough fuel like you are eluding to ..it's symptoms were completely different though....
it would run lean at top end and bog and misfire a bit not a great deal but enough to where you could tell it was running lean the engine was a single cylinder however not a twin so that may well be the reason the symptoms are different for that matter !
the petcock had never been cleaned sense the bike was made !!!! I cleaned it out and that cured the problem
... i didn't go directly to the petcock though I pulled the carb first and found a bunch of water and dirt in the float bowl... that led me to the petcock.... LOL.....
so I don't think this is a case of being lean at top end, unless perhaps the diaphragms are not opening all the way....and that's just the throttle won't open any more..... and that is what sounds like he is experiencing..... it goes fine but after a certain point the throttle changes nothing..... that's either jetting or diaphragms in my book... i could be wrong though...just guessing !
Bob.......
 
i know it's not the clutch slipping. I got new diaphragms in the carbs. Should I experiment with my main jets? Or get an rpm gauge and timing light. I can post a pic of my plugs if it helps. I rode all day yesterday
 
pamcopete said:
Bike goes slow (< 65MPH)

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.
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.
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. Speedo out of calibration. You are actually going faster than 60 MPH! Use your GPS to check the speedo.
9. Tire pressure. Pump up to 32 PSI for high speed.
10. Drive chain too tight. That will rob you of power to the rear wheel.
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.
14. Timing chain needs adjustment.
15. Cheap or bad gas.
16. Low octane gas.
17. Water in the gas.
18. Partially blocked pet cock or fuel filter.
19. Paper filter that has low flow when the tank is not full.
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. Throttle cable not fully opening the throttles.
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
35. Cracked carb boots.
36. Hole in carb diaphragm(s)
37. Cheap pods covering air hole in carb inlet
38. Clutch slipping
Click to expand...

Pete, that was a great list. Jake, all of the above, one at a time until the problem is found. Betcha it will be something that you just glossed over, that's just how it goes.

Scott
 

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