Hello
My C15 is fitted with Amal 622 is fitted with a 120 main jet, 106 needle jet and a number 3 slide, can anyone confirm if this is the ideal base setting.
If this is not the case I would welcome any recommendations as to where I should be starting.
Many thanks
The choke size is the same as the original 375 carb and I would have thought a good starting point would be the original settings:
Main: 140
Pilot: 25
Throttle Valve: 4
Needle Pos: 3
Needle Jet: 0.1055
However, I would test with what you've got, starting with the main jet. If you run the engine at >half throttle on the road for a few hundred yards and then, after stopping the engine quickly, look at the spark plug colour. If very light in colour then the mixture is probably too weak and a bigger main jet is required. Ideally, you need to run with a 130 and 140 main jet and compare the performance to determine which is best.
After the tickover is then sorted, you can test to see whether a No. 3 slide cutaway is too small by how well the revs pick up from idling. If it is too small, the engine will then tend to jerk under load. A bigger cutaway will weaken the mixture between 1/8 - 1/4 throttle.
Many thanks for your response
It's always worth taking into account whether the bike is fitted with an air filter or not. Originally, the C15 was fitted with one but, if it now being run without one, you normally need to increase the main jet by at least 10 to compensate.