dwilfong

Hay guys I am new here and have a project I would like to do.
I am looking at putting a turbo on my Mercury 2.5 outboard eng.
I want to keep it simple and use a blow trough system with the carbs on the eng.
If I just make a box to mount on the front of the carbs this will also include the bowl vents.
Will I need a enrichment circuit as the boost rises or will the circuits in the carbs keep up.
The carbs have a accelerator pump set up that is not used. Can this be used as a enrichment circuit with a boost reference fuel regulator?


also how would you size the turbo for a two stroke eng?


I see there are some smart people on here could use some input.

Matt Cramer

Blow through carbs typically need some extra enrichment - basically a power valve that opens under boost. The accelerator pump won't cut it; this only squirts fuel when the linkage moves, so a continuous enrichment feed would require constantly pumping the throttle. The other option is just using a big enough jet to get a good AFR on boost - this typically means the AFR off boost isn't very good, at least not when it's on the main jet. This is assuming it's a fixed jet carb like a Holley or Weber.

dwilfong

The pump circuit is not used on this carb. My thinking is to tap into the circuit and use it as a enrichment circuit by having a separate boost reference regulator just for this circut that would be set at 0 at no boost. then as the boost comes on it would add pressure to this circuit. Using a jets in the circuit to set the flow as needed.
The carbs have 3 circuits in them ,idle ,mid and high. all having separate jets.