TOPIC:

Hi Scotch/Kawboy,

I haven’t changed any parts within the carbs. All the original parts are in good condition including the diaphragms, needle valves etc. The only parts I’ve changed are the ‘o’ rings on the float needle valves and the mixture screws. Everything was put back in exactly the same order as they came off including the enrichment diaphragms.  

The enrichment system has a small jet pressed into the carb body. I know these were clear as when I injected fluid into the carb body fluid there was a clear stream coming out of the jet. 

Regards

Martin

 I admit I will need to treat the tank with POR-15 or similar in the near future

I would strongly suggest to focus on POR-15. It's proven to be good and that's what some professionals I know online use. 
One product called Kreem, has been advised to me not to use as apparently it can flake and be trouble with even a small amount of flash rust. POR seals absolutely everything, and you can't removed it no matter what. I had some POR residue on my hands after doing my tank, and no amount of scrubbing would help. It took two weeks to have my fingers back to normal self.  

Above this the bike is faultless except at a constant speed of 60/65mph which, is about 3500rpm. it feels as though one of the cylinders has the occasional misfire.

A possibility is you're running lean on the high-speed needles.  Had a similar condition when I tried lowering my needles by 1 slot.  Under acceleration no problem but maintaining hwy speed on level road, the engine seemed to surge which required the throttle to be annoyingly applied a slight amount and then backed off....and then apply a bit....and then back off.....!.   Went back to the middle (#3) slot and it was OK, again.  Depending on altitude, air density and humidity you may be on the "threshold" of your current needle position.  Try raising the needles 1 slot.  This can be done on the bench with only the choke-lever tension screw and the idle screw (between the Left and Center carbs) requiring removal to "flip" the lids.  The choke shaft and lifters can then be wriggled off the plungers.

Thanks for all the advice. I’ll have another go when I return from Spain on 4th August. Any ideas on the oil light coming on. 

Regards

Martin. 

Oil light ideas? None !

The oil warning light is operated by the oil pressure switch and also the oil level switch. The oil level switch has caused a few members trouble when it gets clogged with sludge. Familiarize your self with these two items and check the wiring. The other members ended up pulling the oil pan to access the oil level switch and cleaned the switch. Things got righteous after that.