It is really important to make sure that all the jets and airways are totally clear on that carb. Really thorough clean with carb cleaner, then carefully blow out all airways etc. Things can get gummed up after such a long period of non-use.

I’ve found that these carbs do block up readily, probably because they have so many fine drillings in so many different places it doesn’t take much in the way of debris to start a blockage.

Trouble spots are usually confined to the brass main jet and holder which needs to be removed and thoroughly cleaned, including the cross-drillings in the holder, and also the slow-running jets which are drilled into the inside of the venturi of the carburettor alongside the butterfly; these drillings give a progressive feed of fuel to the engine when the throttle opens. If you don’t clean these out you will find that it may not tick-over at all and it will hesitate when the throttle opens. There is a series of galleries on the outside of the carb body behind the slow running mixture screw that will need to be cleaned and the drillings for the slow running jets can be accessed by removing blanking screws that cross this gallery.

Best of luck with it.

We use an ultrasonic cleaner in our workshop but we find that it isn’t foolproof. By all means use it but more often than not we find that we have to clean the carbs the old fashioned way with plenty of clean petrol on hand, an airline and even a small piece of soft fuse wire to poke the holes out in extreme cases.

Don’t think I’m advising you to poke wire into the holes because that’s the easiest way to enlarge them, then it won’t work at all! Better to try all other methods and if all else fails try a piece of wire, but make sure it’s small diameter soft wire that won’t affect the hole size. Certainly don’t use gas nozzle reamers like I’ve seen someone do years ago- the carb was scrap after he’d “cleaned” it!

You may want to have a look at the section that I did on rebuilding a Norton Big Four engine on a Trusty Steed. There are some pictures on there of the carburettor which you may find useful.

Best of luck with it, it sounds like you’re nearly there.

The tuning of the carburettor has to be done in sequence and somebody that isn’t used to these carbs may not appreciate that.

Firstly you want to screw in the main jet until you feel it stop, then turn it out one turn. Do the same with the slow-running air screw on the side of the barrel. That should be sufficient to get it running.

When it’s running, set the throttle on a fast idle (around 1500 revs) so that the majority of the fuel that the engine’s running on is going through the main jet. Then wind the main jet out until the engine starts to run rough; turn it back in again until it runs rough again, then turn it out half the distance between these limits. This should then be the ideal setting for the main jet.

For tick-over you want to close the throttle and repeat the process with the airscrew on the side of the barrel, adjusting the slow-running screw on the throttle spindle to achieve a sensible tick-over speed.

Best of luck- as Charlie says, if the choke is opening and closing by itself you really want to stop it. It’s not like a car choke, it is purely a cold-starting aid to richen the mixture and the engine will not run with the choke on when it’s warm.