We all have been though this starting issue -

I personally have discovered that I over think in the diagnostics department.

THUS

Resolving starter issues is relatively straight forward
I start with a fully charged bike battery grounded and run power directly to the starter.

For me, 90% of my starting problems have been low voltage, worn, corroded, poor or loose connections at the battery or the starter.

I hope this is where your problems are - otherwise let the over thinking begin . . .

So did you measure if you have the full 12V at the starter solenoid and at the starter ?
I guess worst case would be that the windings of the starter motor are damaged and it has a short.
As it was suggested you can try to connect 12V directly to the starter to see if it turns. If it doesn`t you`ll know the problem.

G.

Still not starting. Solenoid replaced and turning over nicely, but on trying to start it coughs and splutters - no start. A few smoke puffs out exhaust and the odd backfire.

I have also put on Dyno coils at the same time but spark looks good when test against motor exterior. I have new spark plugs.

I noticed a bit of a kink in the fuel hose to the carb so I re-positioned the regulator and replaced hoses.

Due to fire can see a bit of soot on carb butterfly but when open the butterfly I can see no soot on manifold. So carb should be okay, I am thinking.

I suppose I could clean the carb and check properly fuel flowing through carb. That's all I can think of.

Any other suggestions?

Yes, carb must be cleaned and controlled, but if you remove spark plugs you can see if the're wet or not
Otherwise, removing the airbox, you chan see the choke jets spraying fuel when you handle trhottle

Check that your choke and throttle cables are seated in the carb end bracket properly, and have not moved out of position. I had it happen and caused the same no start, with the sputter and spit.

I can see it entirely possible the one to the rear of the carb getting bumped and dislodged in the fire commotion.

Romus, Check the polarity on the coils,if you have one or both reversed you won't get enough output out of the coil to get it started. Checking the spark by taking the plugs out won't work if the polarity is reversed you need a proper spark checker

Also with the dyna coils you may need to widen the plug gap to its maximum range

4. I have undone the starter button, sanded the points and sprayed with elecrtic cleaner.

Have you given the same treatment to the on/off portion of the switch as well? Check your voltage drop across it if not.

Have you checked voltage at the coils? On the 750 at least, I think there are two connectors between the on/off and the coils. Point being, there are points between the start switch and coils that could still cause significant current loss.
In my case it was largely the on/off switch giving me fits at one point. I was setting out to do the coil wiring change and found cleaning the switches was all it needed. The drop across the start switch was minimal compared to the drop across the off/on(run)/off switch.

Warwick,
what was the first repair/modification/change you did after the last ride when the bike still worked fine ? Changed belts, put adjustible cam belt pulleys or touched the pick up bracket ?

G.

I'm with you Gert, coil issue is what it seems like