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Trouble starting ’40-42 16H Norton.........

Chris Preston

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'Evening All,


We have a 1940-42 Norton M/C in our museum's collection that we're working on getting back on the road again after some time sitting on display, but it's challenging us every step of the way back to being operational again. The following is in the words of the chap who's working on it:


"It's extremely difficult to start the motorcycle. The engine will turn over easily and appears to want to catch but won’t engage without difficulty. Continuous adjustments with fuel, advance and air have little effect but engine will backfire occasionally when trying to start. Lately, the backfire is getting very noticeable. Spark is good but plugs show carbonization. I suspect mixture is lean but backfire suggests rich? However, when the motorcycle does start (once every 5 min and 50+ kick starts) it runs very well for 20 sec before stopping. No amount of throttle adjust/control will keep it running. For those 20 sec of running it sounds very good and the bike can be revved with throttle. But at the end of that 20 sec it simply quits.


Spark appears good, and the points were adjusted and spark is good, but I am not convinced that the advance/retard setting is correct - movement is free, but seems to only go half way. Compression is good; gas is good, and so are the oil levels." surrender.gif


Any advice would be greatly appreciated.




Chris Preston,

Ashton Armoury Museum,

Victoria, BC, Canada

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If the spark is good and it only runs for 20 seconds then I would check the carb. A backfire could mean it was too lean or too rich, both are possible under the right conditions. I assume the bike was running OK before it went on static display and was not just popped together for display purposes? Have you tried pulling a plug the moment it stops running? This is the ideal moment as it will tell you whether it dies rich or lean.

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Agreed......you do not mention the carb and carbs gum up easily after only a few weeks standing. Your observation that it does run OK for a short spell indicates the timing and mag are OK which leaves fuel. A good idea would be to take the carb off and give it a good clean (check an overhaul guide for that carb to guide you in cleaning the various drillings) and maybe replace the gaskets.....replace the jet? If you can borrow a carb off another bike, this might help confirm if the carb is the culprit. Carbs also wear out of course and no amount of fiddling will fix a worn carb.....that needs expert rebuild.....or buy a new one. But my money is on a dirty carburettor.

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As Ferg says, the 276 carb is the most likely suspect. Although it's quite a simple instrument, it does have a fairly critical set of cross drillings that can only be cleared by complete dismantling.


If the instrument is removed from the motorcycle and the large mixing chamber nut underneath loosened, you will see the brass base of the jet block. If the slide above is removed and the needle jet underneath, you will be left with the mixing chamber and the interference-fit jet block. The way that I usually remove this is to immerse the body in boiling water and then invert it over a hardwood rod and tap the end down. The jet block should lift out but don't force it as it is a three-piece soldered assembly and the air slide guide above can deform. Nortons have a specific block that is no longer obtainable new and hard to find.


Once the block is out, you will see a number of tiny drillings which include the pre-sized pilot air and fuel feeds. An untrasonic clean is a good idea but some careful wire work is often needed as well.


Flooding (tickling) the carb effectively bypasses the pilot drillings so it will run for a short period.

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