Engine Vibration over 4400 RPM

[Dave58]

I have a 97 1100RT with 19000 miles on it that I bought used this summer. Having previously owned an Airhead, this is my first oil head experiance. I get an engine vibration when I get above 4400RPM, and gets worse as the RPM's go up. It is really noticable when I am in the higher gears, especially 4th and 5th. I can go up to about 75 MPH in 5th gear, and it will be like butter. But as I start approaching 80MPH,(over 4400 RPM) it gets extremely buzzy. The more above 80 I go the worse it gets. I'm talking about a teeth rattling buzz.

I'm pretty sure it's the engine, because I'll pull in the clutch, and it coasts smoothly.

I have new plugs, new fuel filter, new air cleaner, valves adjusted and throttle bodys synced. There are no diagnostic codes. It passes the Hall sensor test. I tried some fuel injector ckeaner, and it seemed to help a bit, but the vibration is still there.

[FNST YR]

I'm interested in this also as I just bought a '96 1100RT that does it ~5k RPM. I'm coming off of a K100RS that was a lot smoother. I was told that the valves and TB were adjusted but I'm gonna verify the adjustments.

[Dave58]

The dearth of responses makes me think that everyone is as stumped as I am. Maybe it's the nature of the beast?

[Ken H.]

The challenge in responding is that everyone's interpretation of what is a "buzzy bike" is different. What one finds quite acceptable and as you say, the nature of the beast, the next person finds as grounds to sell it.

 

Certainly the first step in addressing the issue is a full exacting tune up. Precise valve adjustment, new plugs, detailed throttle body synchronization. Only after that and re-evaluating can one draw some conclusions if the situation is better.

 

These are big twins, and they're never going to be as smooth as a in-line small-bore 4 cyl. Perhaps you can find another couple of samples at a gathering to ride and get a comparison to form a point of reference.

[snod]

One thing to consider is an "Italian Tune Up". If the prior owner tended to lug the engine a bit, there is probably carbon built up on the top of the piston and/or head. Go ride the p**s out of it for a tank or two. WFO for as much time as you can get away with. Then do a good tune. Plugs, valves, aircleaner and TB Sync. There is a buzz in every boxer I have owned, normally somewhere around 4800 or 5000 RPM, but it smooths out again at 5500 or so. There is also a sweet spot somewhere around 4000 or 4200. Ken has a good idea if you aren't sure, ride another one and compare. Stop by, I'll go for a ride with you.

[Dave58]

Thanks for the offer, and the idea. I did have a complete tune up done on the bike. We have reformulated gas up here, which may be part of the problem. If the previous owner left that crap sitting in the tank over the winter, it probably varnished everthing up. That was why I tried the injector cleaner, which did improve performance. I think I'll stop at the dealer to test drive a used RT to compare it to mine.

[tom collins]

I too went from an airhead to a 97 oilhead. The airhead engine is just smoother. My theory is that it is smoother because it does not have the inertia and movement of the chains and high cams to deal with as does the oilhead, or 2 extra valves per side either. both models seemed to have their sweet spot at around 4000 and the airhead would get a little vibey above or below that number, but not as much so as the oilhead. that surprised me too, i now have a twin spark that is noticably smoother than the 97 at all rpms, but i am too far removed from my airhead to compare it to that.

is it too vibey? as other posters have said, it is hard to say from your description. if you belong to a club, chances are that someone else has a similar bike, maybe you could swap for a few miles and check.

good luck.

 

tom collins