Engine Vibration at 4k rpm plus

I'm experiencing some pretty noticeable vibration at engine speeds over
4000 rpm's. It doesn't seem like it's the chain or suspension because the
vibrations disappear when coasting at speed (pull the clutch in and let the
revs drop).
It seems to idle smoothly and throttle response seems normal.
Relevant Data:
1995 VFR 750
15,500 miles
Most likely original R/R, but I have not checked
Due for 16k service soon, so plugs are probably pretty old, valve lash has
not been checked lately either.

So far, the only things I can think of are:
-bad carb synch
-loose engine mount
-fouled plugs

Mike

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On Saturday 16Sep, 2006, at 10:37 PM, blackrifle wrote:

> I'm experiencing some pretty noticeable vibration at engine speeds
> over 4000 rpm's. It doesn't seem like it's the chain or suspension
> because the vibrations disappear when coasting at speed (pull the
> clutch in and let the revs drop).
> It seems to idle smoothly and throttle response seems normal.
> Relevant Data:
> 1995 VFR 750
> 15,500 miles
> Most likely original R/R, but I have not checked
> Due for 16k service soon, so plugs are probably pretty old, valve
> lash has not been checked lately either.
>
> So far, the only things I can think of are:
> -bad carb synch

This will exhibit itself as a lumpy idle long before it causes
vibration. Other symptoms include rough transition on/off throttle,
and surging at steady throttle (can feel like ripples in an otherwise
smooth road).
> -loose engine mount
Slap a torque wrench on your engine mount bolts. You _don't_ want
these things to come loose.

> -fouled plugs

Don't discount the chain and sprockets without at least inspecting
them. A link that's stiff can cause problems under load but not when
coasting. The quick check would be to put the bike on the centerstand
in neutral and spin the rear wheel slowly. If there's any link that
doesn't smoothly conform to the rear sprocket, you've found your
problem. While you're there, you might as well check for missing o-
rings (is one link greasier than all the rest?), which would mean
that your chain is on the way out. fwiw, 15k miles on the OEM chain
and sprockets is typical of units without either an automatic oiler
or an owner obsessed with a clean chean.

Also check that your wheel weights are all there. This is not as
likely as the other stuff, but it's far easier to check.

later,
Johnj
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