Mechanincal Secondaries

[oldtimer]

Hi there,
It is a waste of time to convert to mechanical secondaries. The is no advantage only disadvantages. All mechanical secondary carbies have a secondary accelerator pump circuit to compensate for the huge flat spot that is generated when the secondaries are suddenly opened. Well that's not entirely true, there are many aftermarket carbs that don't. But if you convert your carb to mechanical secondaries, without the extra shot of fuel you will experience what feels like a sudden increase in power but this is not the case. Keep the vac secondaries and tweek them a bit if you have made some performance enhancements to the engine. If the engine is stock then leave the carby alone. If you study the linkages closely and move the promary throttle slowly to full throttle you will notice a linkage makes contact with the secondary shaft as you go to full throttle. This linkage just kicks the secondary throttle off its fully shut position to initiate the opening of the shaft when the vacuum diaphram starts to pull the secondary shaft open. You can bend this linkage a bit to cut it open a bit further and then play with secondary diaphram spring tensions to get a result. Generally speaking though, this type of work is difficult due to access of the components while the carb is still on the engine, so you will be remove & installing the carb quite a few times to achieve a decent result. A properly tuned vacuum secondary will be much better in operation & will be better on fuel usage.
Cheers
Mike