We're making good progress grumpy
I couldn't see any signs of water in the fuel from the float bowl but there was a small amount of fine grit in the container and around the rim of the hole where the bolt goes. There is a good flow of fuel coming from around the pivot point of the float bowl when the tap was turned back on. After putting this back together and running the engine it has improved considerably. There is now no audible signs of the "hunting" and it is running smoothly and powerfully at the max power setting. The only apparent problem now is that it still won't run when the lever is moved much below the half throttle position. I guess I will need to move on to the next step in your last post to fix this. I'm probably running out of daylight now and I'm otherwise occupied tomorrow so I'll get onto it again on Monday and post my results.
Many thanks for your help so far. Very helpful.
Cheers
