I have my XT600 3AJ loaded with luggage and the front does feel very light it handles ok on the flat but any bumps can be a bit hairy.I think there is a plastic knob on bottom of shock.Is it just a case of turning this to stiffen or soften suspension or is it not that simple
I know I should have looked into this before leaving England but guess now is a good as time as any;
Thanks
John

Bolla,
If your 3aj is similar to my 1989 U.S. model xt 600 then the plastic knob controls only the rebound damping. To increase or decrease the spring preload you need to move the two large toothed nuts (they look a bit like sprockets) that thread onto the bottom of the shock absober below the spring. You need the two suspension adjusting tools in your bike's tool kit to do this, but in a pinch you can use a flat bladed screw driver and a rock as a crude sort of hammer and chisel. First loosen the bottom nut (this is the lock nut) then turn the top nut in the opposite direction, so that the length of the spring is shortened. When the suspension has been suitably stiffened, tighten the lock nut back up against the top nut. Be careful not to go too far with the top nut. If you take it off the threads I'm guessing it isn't easy to get it back on (if it's even possible with out disassembling the shock). A few turns of the top nut should make a noticible difference.
Good luck,
Nate

Thanks for advice Nate
Had a look at the adjusting nuts,I have about 1cm of thread showing from bottom of shock up to the adjusting nut do you know how much threads there are
I would think there is more then 1 cm so I should be able to stiffen spring
Is it easy enough to do with the bike on side stand or should I try and get rear wheel off ground or put bike on its side
Thanks

Yeah,
There should be more than 1 cm. It sounds like your rear suspension is in the factory preset position, so you are right about in the middle and going up 8mm or so should be fine. On mine you can see how many threads are left if you look at it from just the right angle (try sticking your head in between the rear wheel and the shock). Doing the adjustment on the side stand is no problem, just make sure you don't go too far!
Enjoy your ride,
Nate

Hmmm...
On looking at my shock again, I have about 15mm showing and it is very nearly at the maximum upper level. I think you should try going up a half centimeter (instead of 8mm) and see if that improves things. (Again this is all assuming that we have the same shock).
I hope this helps,
Nate