Hi Rod,
I've fitted a number of twin strombergs to early Holdens and have only fitted the vac advance to one carby (the brass fitting above the throttle plate).I don't think it would make any difference in vacuum if it was connected to 2 carbies.
Dave EH,
Mechanical advance is the second method of ignition timing advance. As the distributor spins fast enough to activate the mechanical-advance weights, the engine receives initial timing, mechanical timing, and vacuum timing under part-throttle conditions. As the engine accelerates to wide-open throttle, the vacuum drops, eliminating the vacuum advance timing. For example, part-throttle total timing would look something like this: 10 degrees initial + 10 degrees vacuum + 20 degrees mechanical = 40 degrees of total timing. At wide open throttle there is no vacuum present and the vacuum advance timing is eliminated, giving your engine a total of 30 degrees timing. The reason your engine is able to cope with more timing at part-throttle is because only a limited amount of air and fuel make it into the cylinder at part-throttle. Lower cylinder pressures enable the combustion process to start sooner and help improve part-throttle response by increasing torque.
ACE
