04-11-2017, 11:10 PM
Hi Robin,
Hopefully someone will remind us how to access that information, as you say there is a lot of knowledge out there.
In the meantime I can say that I fitted an 1 1/8" SU to a late type original manifold and found that it ran very sweetly with minimal setting up. Needle I believe was either M7 or M9. I'm not sure what spring, probrably the lightest. (Standardish 2 bearing engine with H/C head).
Subsequently I have fitted a 4 branch steel manifold with an 1 1/4" SU; this gives more power and is free-er revving but has proved to be horribly tricky to get right. All the variables have become absolutely critical - ignition timing, plug type, petrol brand, ambient temperature etc all have to be spot on. Running during the winter months has become such a chore that I am thinking of going back to the previous set up. How much of the cause is the carb and how much the manifold I'm not sure but I'm inclined to blame the size of the carb. Needle is FI with about a thou of material removed between stage 2 and 3. The free movement of the dashpot piston is reduced to about 5 thou.
Having said all that you will read under the "leaking carb" post that another contributor has had instant success!
Peter.
Hopefully someone will remind us how to access that information, as you say there is a lot of knowledge out there.
In the meantime I can say that I fitted an 1 1/8" SU to a late type original manifold and found that it ran very sweetly with minimal setting up. Needle I believe was either M7 or M9. I'm not sure what spring, probrably the lightest. (Standardish 2 bearing engine with H/C head).
Subsequently I have fitted a 4 branch steel manifold with an 1 1/4" SU; this gives more power and is free-er revving but has proved to be horribly tricky to get right. All the variables have become absolutely critical - ignition timing, plug type, petrol brand, ambient temperature etc all have to be spot on. Running during the winter months has become such a chore that I am thinking of going back to the previous set up. How much of the cause is the carb and how much the manifold I'm not sure but I'm inclined to blame the size of the carb. Needle is FI with about a thou of material removed between stage 2 and 3. The free movement of the dashpot piston is reduced to about 5 thou.
Having said all that you will read under the "leaking carb" post that another contributor has had instant success!
Peter.