Intermittent Vibration Issue

[swifter78261]

Hello all! I'm relatively new to CB's and the forum. I look forward to contributing around here!

I recently bought a 1982 CB750. Its in great shape, starts without issue every single time, and seems to run just fine. Except that at highway speeds above 55mph, I have an intermittent vibration. This vibration lasts about 2 seconds, will disappear for 2 seconds, then reappear for two seconds, etc. Its like it comes in waves. I can't really tell where its emanating from either. The wheels seem balanced and aligned and there are absolutely no problems at lower speeds. I know what front end shake looks like, and I dont think this is that. I never feel out of control like I'm in danger of a tank slapper. Just a stiff vibration that shakes everything for two seconds on and off. Anyone have any ideas here?

Thanks!

 

[dirtdigger]

Does it do it in more than one gear above 55mph. 4th and 5th above 55 or just 5th above 55. Same road or will any road make the same condition. Road surface condition will cause different vibrations and such. All bikes with have a spot where there is a noticable buzz or a harmonic. Some are just worse than others.

 

[swifter78261]

Thanks for the response! The vibration happens in any gear above about 50mph on any surface. I can't imagine what it would be in the engine - it runs more than fine at all RPM when standing still. I'm also familiar with harmonic vibration, but this doesnt seem to be harmonic as its not a buzz, so much as a vibration, and I cant push out ahead of it. Its more like a shudder that comes in waves every two seconds. Could this be a fork issue?

Thanks again!

Does it do it in more than one gear above 55mph. 4th and 5th above 55 or just 5th above 55. Same road or will any road make the same condition. Road surface condition will cause different vibrations and such. All bikes with have a spot where there is a noticable buzz or a harmonic. Some are just worse than others.