Carb set up

The carbs fitted to Commando Combat were the dual Amal 932.

Throttle valve 3: Needle Jet 0.106: Needle position, middle notch with out silencer mutes. Top notch with silencer(muffler) mutes.

Main Jet, 220 with out, silencer mutes. Main jet 210 with silencer (muffler) mutes.

There was a handbook issued by Norton Villiers Ltd, for the Combat Commando's, which was part number 062864

Excuse the basics, are you sure that the cables to carbs are correct, and not the choke cables, both will fit and work, but if I remember correctly the choke cables will not allow the slides to rise fully, but it would get you home. Check slides are lifting to enable to clear the bore, 

Good fuel delivery needs to be checked, strobe timing, though unlikely, and finally substitute the ignition coils. 

Often the first sign of a cam lobe worn away is when the engine fails to pull higher revs. It might tick over fine and run at lower revs without issue. Look at the valve travel (with the rocker covers removed) while slowly turning the engine over. All four valves should have similar amount of up and down travel. Easy thing to check. I had one exhaust valve moving less than 1mm but the engine still ran up to about 3,000 revs (50mph) fine.

David:

Do you mean that the bike will not rev past 4000rpm in any gear?

Or do you mean that it will not rev past 4000rpm in 4th on the motorway?

Mike

David........as Ashley and Alan both say........you really need to check more than just the carbs. A fuel flow problem would probably result in the engine cutting out.

Limited revs can be caused by a knackered camshaft,  incorrect camshaft timing or poor ignition timing. It may pay you to have a look at the timing cover gear just in case the pinions are not set up correctly. Perhaps the advance/retard mechanism is faulty. or the ignition timing not advanced enough.