Here is the latest if anyone's interested.
My friend rebuilt the carbs, fortunately he had all the parts needed.
I collected them but struggled to get the new throttle cables set up correctly.
With the cables set in the mount at the carb end, even with the adjusters at the throttle and carb ends fully wound in I couldn't get any free play on the cables.
I had to make a bracket which I mounted on the top of one of the carbs and this effectively gave me the free play I needed in the cables and the throttle grip now springs back as it should.
The choke cable had seen better days so I bought a new one which I again had difficulty fitting due to the cable guide in the switchgear and carb mounting being worn. I had to re-mount the cable guide by drilling out the bolt and fitting a larger diameter one with a lock nut as this had previously been bodged when the thread was stripped by a PO.
I re-fitted the carbs and airbox and using a funnel attached to the fuel pump as a remote supply attempted to start the engine.
Next up I couldn't get the starter to work properly-just a click at the solenoid. Thinking the battery was dead or dying and this was confirmed by a low voltage reading on the multimeter I ordered a new one.Had to buy another multimeter as well when I dropped my old one on the workshop floor!
Unfortunately the new battery didn't resolve the problem.
Working with help from friends the problem was identified as either the starter leads (corrosion or a poor connection) or the starter motor or solenoid.
I checked the leads and the main positive terminal from the battery to solenoid was badly corroded so thinking this was the route of the starting problem I got a new one, modified from the local bike shop (QB). The original starter lead is NLA.
I fitted it all back and ....still just clicking at the solenoid.
With help from my mechanic mate and borrowing tools from another friend I then managed with some difficulty to get at the 2 10mm headed bolts on top of the crankcase using a 1/4 inch drive swivel ratchet extension to remove the starter motor.
I took it to my mechanic friend, taking advantage of the first nice weather in months to ride the 56 mile round trip on my 250RSA yesterday.
Upon splitting the motor one of the brushes fell to the floor in pieces, with some other components and the other brush was very worn. The solenoid was tested and also found to be not working.So I've ordered new brushes and a solenoid and my mate will make up some plastic bushes which have also disintegrated. He'll also fit a new bearing to the starter motor.
And so the fun and games continues............