The bike has the standard 389/228 and 689/228 Monoblock carbs. I do not know what the port size is for that carburetor. Please reply if you know. I believe the bike is pretty standard from birth. Does have EV forged pistons and gapless rings I installed. I replaced bearings, and bushings. EV serviced the valves and springs. I also installed an SRM oil pump. Alternator is original, I am running with points, but I did change to the newer point set and auto advance. 19" wheels. Does not leak oil from engine or primary. I get a few drips from the chain oiler/ breather after long spirited rides. I am used to a lower RPM at speed and the 4,000 from the BSA scares me a little. I feel the same "tension" on my 73, 850 Norton Commando as well. But the Norton is silky smooth. Up to 3,500 rpm the BSA has a comfortable balance of rhythm in sync with the exhaust tone. As speed increases, I am reminded of something more similar to riding a paint mixer from the local hardware store. However, getting above 4,000 the frequency seems to become less "repulsive", but more concerning. Either way, I love to ride my BSA. ITs my go to for the biggest smile on my face. I guess I will need to count how many teeth I have drive and driven.
Without looking in the AMAL book saying 389 covers a multitude of carb sizes, however in the earlier models with 389 carbs used were 1 1/8". As no 1 1/8" carbs were ever made as 689 (the opposite handed variant) its most likely your carbs are 1 5/32".
Whether the port size correctly matches the carb or not is a different kettle of fish, so yes the only real way of knowing is counting the teeth. 47t rear drums almost all have bolt on sprockets (earlier fixed sprockets are easy to spot with 47t) most fixed sprockets were 42t with the steel (chromed or painted) back plate (aluminium with bolt on sprockets) the chain runs very close to the back plate. Good luck counting the front sprocket.
a handy ref for old AMAL carbs http://porklips.org/~mason/moto/amal_specs.html
Alan says "As no 1 1/8" carbs were ever made as 689 (the opposite handed variant) its most likely your carbs are 1 5/32" Not true if the porklips side is correct A50 wasps had inch and 1/8th LH monos as did a few others.
Last edited by gavin eisler; Yesterday at01:23 PM.
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