VB 600 slight judder

[MarkOgden]

At speed and off the throttle the VB 600 judders - very slightly. Not much, but discernible. I have cleaned the clutch plates and ensured the pressure plate has an even gap by adjusting the 5 springs. Incidentally a couple of the friction plates look well down - which may explain things somewhat. Anything else I should check apart from clutch? I'll certainly check the points gap and clean them. Timing is OK. I wondered about the carb? It's a fairly numb thing but maybe move the needle up or down a groove? I think I'll clean it out at least ......

[SEDoan]

A little difficult to understand what you mean by judder, but I have experienced 2 carb related things that might be judder. The first is full-throttle acceleration in top gear, then quickly closing the throttle the engine seemed to stumble. The cause was excessive richness and reducing the main jet by 1 size solved the problem.
The other occurred at about 25 mph and about 1/8 throttle, most often when following other traffic on a level road. When closing the throttle slightly the bike surged slightly. The solution was to raise (I think!) the needle 1 notch. If that makes it worse, then lower the needle.
There might be other things that result in judder, loose axle or wheel bearings? Loose gearbox mounting?
Let us know what you find.

[MarkOgden]

I have since lowered the needle to lean it out a little and the judder seems to have reduced. To clarify, when I came off the throttle, the bike did indeed seem to stumble a little. I'll ride it around a little more to verify.

Another point if I may. I did the timing recently with the lever at full advance. However, I think I overdid the point at which the points break a tad too much. With the lever at full advance/fully forward, the timing seems over-advanced. This is no problem as I can pull the lever back a liitle to get the timing spot on - fine. However, if for whatever reason I inadvertently run over-advanced, could this cause overheating of the exhaust/valves?

[SEDoan]

Hi Mark, In general running too much advance overheats inside the combustion chamber resulting in "pinking" AKA detonation which can damage the piston edge. Running too retarded can overheat the exhaust valve if the mixture is still burning when the exhaust valve opens. At least that is how I understand it.

BTW - a mixture that is too lean is more likely to run hot and detonate than a rich mix. Apologies if you know this already.

You can reduce the fully advanced timing a little by backing off the cable adjuster at the mag. Shorten the adjuster and you won't have quite as much advance at full lever (this is for tight wire advance).

Hope this helps!

[john.whiting]

In a low compression engine,its easy to run with excessive advance without any signs .....no extra power,probably less and very high loads on the bearings ,leading to crankpin breakage and roller failure.

[MarkOgden]

Thanks Gents. As mentioned, I have lowered the needle one notch thus leaning the mix out. I also ran it at possibly excess advance with the lever fully forward (tight wire advance by the by). It seemed to overheat a tad, as the exhaust which is normally chrome colour turned a shade brownish after a run. The bike also felt hotter. Therefore what is causing this - the mix or the excess advance? I'll retard it a bit, ride it again and see what happens.....

[dave.owen]

The last comments suggest weak mixture

[MarkOgden]

Took it for another spin. Lever pulled back abot 1/2" from fully forward, Ran very well, did not appear to run hot, but judder still there. Not as bad but noiticeable. Has another look at the clutch plates, and have decided that 2 of the friction plates look borderline.I'll replace them and the springs whist I am at it and give it another go.