I know, its not a BSA but the TOMCC don't seem to want to part with their knowledge. Just bought a Cub which has stalling issues on pickup from a standing start. I got some good feedback from other avenues who use an Amal Concentric 600 but just couldn't give me the jet sizes. Has anyone here got a cub with an Amal 600 who knows their jet sizes please. Or uses a different carb. At the moment it has a 376/272 Monoblock.
You didn't say what year your Cub was? The 1960-61 Cub used a 275 carb with 100 main jet, 105 needle jet, 3.5 throttle valve, No 3 needle position and 25 pilot jet. The choke size was 25/32" equivalent to 19.8 mm.
If you are now using a 600 carb with a choke size of 20 mm, I would have thought a good starting point would be the same settings as for a 275 carb. If it isn't fitted with an air filter then add 10 to the main jet.
Sorry, slightly mis-read your post and see you are using a 376 carb not a 600. The 376 is not ideal since it has a choke size of 24 mm but, despite that, the Cub's 20 mm inlet choke size will be the limiting factor and so the 375 (not 275 as typed in previous post) carb settings should still apply as a starting point.
Hi Spaceman
We think it's a 1965/66 model. It's just going through the dating process. I asked quite a few youtubers what they are using and most of them said an Amal concentric 600.
Can you measure the engine inlet choke diameter?
If 15/16" (24 mm), a 376/272 carb may be correct with a 140 main jet. This would make it a sportier Cub
If 25/32" (20 mm), a 375/44 with 100 main jet may be correct for the bike. This would make it a standard Cub.
Its a 24mm inlet.
That would seem to make the carb the correct one for this Cub. The settings should be:
Main jet: 140
Needle jet: .106
Needle Pos: 3
Throttle Valve: 2 1/2
Pilot Jet: 20
It would be interesting to know how these compare with your carb's setting?
Just to add that a 600 Concentric with 20 mm choke is suitable for the standard Cub but, if your inlet is 24 mm, you ideally need a 624 Concentric. If you went this route, a good starting point would be the same settings as listed above for the 376/272 carb.
Hi Spaceman, I took your advice and installed the 600 concentric Premier 24mm and all my troubles have gone. The bike is running fantastic without any stalls, and ticks over like a watch. Thank you.
Bob
Very pleased for you and the Tiger Cub! It's always amazing how much difference a new carb makes and how much an old carb can be found to be worn out.
Looking for a 275 carb for a cub, any suggestions. Cheers.