the 39mm FCRs are excellent for power and throttle responce. SEt up fairly straight forward. Tuning options are much greater than those of the 36 CVK carbs.
However, if you are looking to improve fuel economy then going to a larger bore racing carburator is not a good move.
I am getting about 40mpg with my current set up.
05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter
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