Grouling and rough vibration from engine

Can any one help I have a 1981 Kawasaki KZ750E 25K Miles round about 50 /55 mph 4500rpm I get this grouling sound from engine or transmission with vibration through the foot pegs
Increasing speed it seems to disappear ,I was wondering about the cam chain adjuster or rear chain ( there is slight polishing on one side at intervals as though it has been rubbing on the casing )
Has any one else experienced this ?
Keith

When was the last oil change, and are you using oil that's motorcycle rated? If you have the stock cam chain tensioner, I'd suggest getting a manual one. Here's a good one:
www.clems-garage.com/CCT/

I'd re-adjust the drive chain, and center it to avoid rubbing, as it's horsepower drain & could damage your chain cover.

Hi Kieth,
I have a '80 KZ 750H with 51,000 miles on it. It has a vibration at about 4000rpm until maybe 4300 or so. I have taken the motor down to the transmission shafts, also checked and welded the inner exhaust pipe liners without finding any vibration source at all. Otherwise bike runs smooth and strong and I have stopped worrying about it! I'd be interested in knowing what you find on your bike though.
Best wishes
art

If you have a polishing on one side of the chain that is a strong indication that the chain is out of alignment. There are lots of articles and methods on how to align the chain/wheels, including this one: motorcycle chain/wheel alignment
I use a very inexpensive tool from Motion Pro Motion Pro Alignment Tool
I would also check the nut on the front sprocket to make sure it is not coming loose.

Growling implies a low frequency vibration. That means you are looking for something that happen much lower than "the F below middle C" (4400 RPM is about where you get "Middle A").

Things that turn that slow are almost all related to wheels and output side of the transmission. To further check, when you get up to speed, pull the clutch and let the bike coast for a few seconds. If the vibration follows the engine instead of the wheel, you know the problem is in the engine.

The transmission will be following the wheels, so if the vibration follows the bike's speed, the problem could be in the transmission. In this case, you can't discount the possibility that you might have a wheel/tire issue.

If it stops as soon as you pull in the clutch and the speed and RPMs don't change, look at changing your oil to one that is JASO-MA certified.

Finally, I've heard (and even experienced with my 440) that phantom vibration. For me, it didn't happen all the time because I seldom drove 55 because I was in Germany it was either 'reasonable' speeds or completely 'unreasonable' speeds.