Pinched this from another site but well worth passing on for any of you guys having problems with colman petrol stoves:
A quick fix
that does work most times take the generator off put it in a pan of simmering water with a little fairy liquid let it gently simmer for 10-15mins this will remove the carbon build up on the needle part generators dont normally wear they just get a carbon build up.
It worked for me thought mine had expired but after following the above, as good as new, well chuffed saved me £16 that I was quoted to replace it. :)

If you are on a session the expiry of your Coleman can be a problem. The yanks have come up with an idea to make a temporary lightweight stove, so you can keep going.
The thing is so light though you can make it at home, and carry it as a spare.
It runs on Meths by the way.

See here:-

http://en.wikipedia.org/wiki/Soda_can_stove

BOF ;)

I've recommemded this before, but if you use Shell or Texaco normal unleaded you shouldn't get carbon build up. I used to get through a generator a year until I changed, now I've had the same one for nearly ten years. I also add a few drops of Redex too, just for good measure. Decent petrol contains the detergent additives necessary to keep your car engine clean, and hence works with the colemans.

This is the coleman 533 that i use and its the best stove i'v ever had.Put your old gas stove away safe and buy one like this
I'v been warned thay can flame up but i just pump it 20ish times then light it outside my bivvy then pump it 20 more times.When she has warmed up its mint.I use it inside my bivvy with door open but when i turn it off i do so outside thay dont smell to good when you turn them off.
I treat the pump seal to some 2in1 oil once a year.
Should i give this some redx then?

Yes Duds, I add the redex, it definately works. stay away from crap petrol too, Shell is the stuff.