Forks and vibration

[machten]

Hi,

I have a query regarding vibration and my front forks on my 68 M3D 250 as I don't know what I should consider "normal".

Firstly, I'm currently running a VHB 29 carb as that's what it had when I got it. I have the right SSI but haven't got around to fitting it because:

(a) the VHB works pretty well
(b) I had to get some bits for the SSI (but I've had them for a few months now )
(b) I haven't had the time to make up the new throttle cables it will need.

The VHB has a bit of a searching idle. I haven't tried to address that as I keep telling myself I'm going to put the SSI on. As the idle goes up and down, at traffic lights for example, at certain revs below the 2K base of the veglia white face tacho, my forks start working up and down. If I put the front brake on, it stops.

For some context, the engine is actually very smooth. I experience some vibration at about 4000RPM but at about 4500 it smooths out and I have very little vibration up to the 7500 I'm game to take it to.

I was wondering if the behaviour of the forks at idle is indicative of a damping (or other) problem, or if it is just "normal". The forks seem to work very well in general and spirited riding - in fact it suprises me how well they handle some fairly ordinary roaqd surfaces.

Kev

[graeme]

Hi Kev, my 450 is exactly as you described your 250.
Graeme

[Harvey]

Hi,

I have a query regarding vibration and my front forks on my 68 M3D 250 as I don't know what I should consider "normal".

Firstly, I'm currently running a VHB 29 carb as that's what it had when I got it. I have the right SSI but haven't got around to fitting it because:

(a) the VHB works pretty well
(b) I had to get some bits for the SSI (but I've had them for a few months now )
(b) I haven't had the time to make up the new throttle cables it will need.

The VHB has a bit of a searching idle. I haven't tried to address that as I keep telling myself I'm going to put the SSI on. As the idle goes up and down, at traffic lights for example, at certain revs below the 2K base of the veglia white face tacho, my forks start working up and down. If I put the front brake on, it stops.

For some context, the engine is actually very smooth. I experience some vibration at about 4000RPM but at about 4500 it smooths out and I have very little vibration up to the 7500 I'm game to take it to.

I was wondering if the behaviour of the forks at idle is indicative of a damping (or other) problem, or if it is just "normal". The forks seem to work very well in general and spirited riding - in fact it suprises me how well they handle some fairly ordinary roaqd surfaces.

Kev

That is a function of the crank balance. I rebalanced my 450 to 70% to balance the vertical component, more that the horizontal component. The result is it is smooth over 4000 to 9000, but the horizontal balance is worst, and I had to hold the front brake on at lights to stop the front wheel from moving back an forth.
A bit embarrassing when you start it up on the stand and it walks away.

[machten]

OK. Thanks for that guys.

Sounds like "situation normal" then.

Kev