TM250 engine balance problem

[GMC]

I have a TM250 powered, period 4, road racer and I'm having a few issues with vibration.  In fact when I sit on the bike and rev it, it feels like I'm having a prostate check such is the terrible vibration. 

That statement seems to indicate that the vibrations are bad when you’re not actually going anywhere, not just when you have it screaming down a straight.
If that’s correct then I’m not so sure it would be the balance factor of the crank.
My logic says the balance factor would mostly come into play when peak revving down straights.

So…
How long has it been like this?
Has it always been like this since you have had it or has it started to be like this recently?

Is it a TM frame?
If not who put the motor in what frame? – maybe the engine mounts aren’t strong enough?


Bought a bike a few years back and during the rebuild it was found that the gearbox input shaft was bent, obviously someone had used too much force on the clutch for some reason.

[chrisdespo]

When you sit astride the bike does it feel like the engine squirms around when you give it a rev you would mostly feel it when the revs are dropping .? if so it would more than likely be main bearings. if not lookat the engine mounts. i think you said it was fine in a different frame.
i Ran an RM250A engine in a real nice T250 road frame back in the seventies it was good but vibrated badly first run remaufactured the engine mount plates and fixed the problem.
the other thing that i had trouble with was a 350 kwaka single (Big Horn) and you had to get the gearing right so i would run in the right rev range, from memory the kwaka was what you would think over geard and the same for the suzie plenty of clutch slipping off the line for sure.kept the revs down to managable level .

[Simo63]

Thanks guys, plenty of helpful hints posted so far.  I've been working in the garden over the weekend (have to get my brownie points up with the wife) so haven't had much chance to respond.

TM frame modified for road racing but standard around the engine cradle.  No cracks that I am aware of, engine vibrates badbly when sittingon it and revving it.  Will check all the things listed and get back with what I find but I've got a busy couple of weeks ahead (trying to get my TM rebuild for Connondale Classic for one) so the road racer is low priority at the moment.

Cheers
Craig