OK, so I've splashed out and got my original rear shock with reservoir rebuilt and fitted with a new bladder courtesy of Brook Suspension (cost a shedload!)
The only problem is that I can't find anything on the net about how to set these shocks up correctly.
I know how to adjust the preload using the adjuster rings, but can someone tell me what the black dial (circled in the image below) at the base does exactly?
It's got the numbers 1,2,3,4 on it.
I weigh about 70kg's with all my gear on, so some advice as to what setting I should be using would be most appreciated.

That shock looks mint. That dial is the 4 way adjustable rebound speed. No 1 would give the fastest rebound speed, and no 4 would give the slowest (most) rebound. It will be easy to verify this when the shock is fitted.
As it's a Suzuki road shock I would imagine that all the settings are safe to use on the road, ie not too dramatic. You want to dial in enough rebound to not pogo you out of the seat after serious bump, but you definitely do not want too much, as this will make the back of the bike sit down, and weave from the rear.
Set it on 2, and go for a ride. You can bounce the rear of the bike in the garage to get a rough feeling of how the shock is rebounding. I like reasonably fast working suspension, as I do a fair bit of track work, and I find that keeps the tyre on the tarmac better for my style of riding.

Wicked.
Thanks moforockband.
Useful feedback and no messing around as usual.
I'll do some bouncing when it's all back together.
I do like a clean tidy shock, so it was worth the money.

LOL. How much was "a shed load", Hubbskiboy ...if you're not too embarressed about how much the rebuild/refurb cost.

Hi Wullie,
I'm not embarrassed about the rebuild cost.
I would spend all my wages on the bike if I had too, because it's all I care about at the moment.
We all need a hobby don't we?
Anyway, I've sold the Triumph Daytona, so I've got a few quid in my back pocket now.
The shock rebuild cost £260.00 all in.
Brooks did sting me on a new eservoir bladder that apparently 'had' to be replaced.
You just have to trust people in the end.
They also'lost' the push on black plastic cap that goes over the top of the screw on valve cap, which pissed me off a little.
I called them and they said it got damaged in the process, which is bull, because I took it off easy before I sent it.
I'm struggling to find a local fairing repair and respray shop at the moment.
The one I used last time - Arnolds Fairings - has closed down!

I'd imagine the reservoir bladder is very important in keeping the nitrogen charge in the shock, so well worth replacing. However I wouldn't let them off parts being lost. I'd be asking for compensation on the lost part esp after £260 shelled out.
They made a fair bit of profit there, so claw some back!