1972 Honda CB750K2. Clutch started slipping at high speed (over 75mph). No noticeable slipping at lower speeds even when punching it through the gears. Also has a slight chatter when sitting in nuetral, stops the chatter when clutch is pulled in disengaged. Any ideas??

It sounds like the issue with your Honda XLR125 (1998) not picking up speed in top gear could be related to a clutch problem. If the clutch is slipping, it could be causing the engine to rev high and prevent the bike from reaching higher speeds. Clutch slipping is often a result of worn clutch plates, which can cause decreased friction and ineffective transfer of power from the engine to the transmission.
Based on your description, it may be necessary to replace the clutch plates to resolve the issue. If you're unsure about the condition of the clutch, I would recommend having a professional mechanic inspect it to diagnose the problem and recommend the appropriate repairs. It's important to address any clutch issues as soon as possible to prevent further damage to the engine and transmissio

Common causes of a mechanical misfire are worn piston rings, valves, cylinder walls, or lobes on a camshaft; a leaking head gasket or intake manifold gasket; damaged or broken rocker arms; defective fuel injectors (and/or the electronics that control them); and a slipped or incorrectly-installed timing belt or timing chain. Generally, this type of misfire has more of a "thumping" feel to it. It is usually noticeable regardless of engine speed; in fact, it may even intensify as the engine speed increases

If engine revs increase but road speed does not increase, your clutch is coming to the end of its life and needs to be replaced

I understand that your engine accelerates fine to high RPM's but your car won't move. Since it is a manual transmission car, the problem may be in a slipping clutch. Probably your clutch is worn and slips.
You might need to replace your clutch.

If the transmission is slipping then you will need to replace your clutch plates. you don't say how old the bike is, so this may not be the case. But you should check the adjustment of the clutch lever anyway.

Is this a standard transmission or automatic? It sound as though the clutch (standard) is slipping, or the transmission (automatic ******) is slipping. Does this happen only when starting off from a stop, or only at highway speeds? There is very little chance the tach is reading the engine speed incorrectly. If so that would look and feel as though the engine was not revving up, as your speed isn't increasing even though the tach shows higher RPMs.

The clutch is non adjustable if the clutch fails you will have drive all the time or it slips. if the tines spin at the same speed with the engine at low and high speed the clutch might be slipping, the common cause for this is the gear box is partly siezed due to no grease being pumped into it, most ppl dont even know about this untill its too late. you have to remove the LH side tines to get to the screw.

If the bike is reving high in top gear but you are not gaining speed or very little speed your clutch is slipping. This is a sign the clutch needs replaced.

start the car andwith your foot on the brake shift it into 3rd or 4th and slowly release the clutch the car should stall out. if the engine continues to run then the clutch is slipping. Another thing to do is while driving punch and hold the gas. Do the rev suddenly jump up while the car stays at about the same speed or just slowly increases in speed? if so then the clutch is slipping. Get a Haynes manual (autozone for about $20) and see if there is any adjustment fore the clutch. The manual should also have some sugestions for checking out the clutch.

If the car rev'd up but did not speed up at the same time the clutch is starting to slip. Check the adjustment and recheck driving. When the clutch starts to wear this is how they act, only most people ignore whats happening and keep driving till adjustments won't fix it and the clutch has to be replaced. Have adjustment checked and keep an eye on it and hopefullty you won't need a clutch yet.