carburettor tuning

Information relating to Matchless and AJS Models built prior to 1939
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sbrock
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carburettor tuning

Post by sbrock »

Hi 1940 model 8 500 OHV. When tuning the carby what position should the adv/retard be. Also threads in the tank are 3/8" UNF. What size and thread should they be BSF or BSC. Is there enough meat to heli-coil them
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SPRIDDLER
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Re: carburettor tuning

Post by SPRIDDLER »

sbrock wrote:Hi 1940 model 8 500 OHV. When tuning the carby what position should the adv/retard be.
Hi Simon.
When static tuning the pointed pilot (air) screw on an AMAL carb with the bike upright I leave the A/R in its normal position for starting, i.e. partially retarded, aiming for a slow steady tickover and clean pick-up. When adjusting the screw you should start with it about one and a half turns open (unscrewed) and end up with it somewhere between 1 and 2 turns open.
Just as a guide, if you end up with the pilot screw less than one turn open you may have an air leak at the carb/cylinder head interface. If it ends up more than 2 turns open it may be that the float level is too high.
Or it may be none of the above. ;)
The main jet and slide cutaway are not 'adjustable', except by substitution with alternatives after road testing.
Here's a guide on carb tuning
http://www.hitchcocksmotorcycles.com/mo ... to-tune-up


Can't help with the thread question but wasn't there an article in a recent 'Jampot' mag about repairing tank fixing brackets?
Last edited by SPRIDDLER on Wed Feb 17, 2016 12:14 pm, edited 4 times in total.
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Rob Harknett
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Re: carburettor tuning

Post by Rob Harknett »

In the petrol tank you should find 26 TPI cycle thread except for the petrol taps which are a Gas thread.
Check the parts list of the threaded tank fittings, it gives the sizes.
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