Racing Fuel Systems

I am thinking about the relationship between secondary MAB and fuel curve in carbs with secondary plates. Tell me if my assumptions are correct...

With a conventional block with two 0.026-0.028" e-holes, it is well established that opening up MABs tends to make it richer when the mains first activate, and leaner at the top end of the fuel curve. Agree?

With a plate, as I see it, there is zero air bleed into the main well. Air is introduced above the main well prior to booster entry. Agree?

Am I correct in assuming that larger MABs will behave differently with a plate? I am thinking that a larger MAB might actually delay main circuit operation and make the whole curve leaner, since there is no air being introduced at fuel level, as you would have with a metering block. Does this sound right?

Agreed, and sort of agree, lol...

I don't see the "e-holes" (a better term is 'booster correction bleeds', where Mark has indicated that their job is to counter a booster in a venturi's tendency to veer too rich with increasing airflow past/through it) job, unless located above fuel level, which I don't believe is a good thing, as admitting air below fuel level, "bubbles", into main wells' fuel...
I think the newfangled term "emulsion" has confused the issue...

I would imagine that increasing MAB size above a metering plate would act the same as above a metering block, as to initial onset and WOT air:fuel... because MAB air is introduced into air:fuel above fuel level in either case...

Now, I don't know enough about the function of the plates, but the arrangement of their passages must do somewhat the same as the booster correction bleeds in a MB does... dunno... tuner had mentioned somewhere that the connecting passages between vertical passages were for acceleration enrichment... so, in a roundabout way, maybe that enables the boosters to function as if with a metering block?...

I agree it would act more like a kill bleed as it is directly connected to where the fuel flows.

I am curious on the function of the secondary metering plate. I’ve never played with them but staring at a pic of one for about half hour it looks like:

*As booster signal overcomes (outpaces) mab it begins drawing fuel from the side parallel channel as this channel is narrow and less voluminous, easier to move fuel. It is fed through the connecting hole of the larger main channel.

*As demand exceeds the flow capability of the connecting orifice it lowers the fuel in the side channel and begins drawing fuel from the larger main channel.

*Side channel would then have a lower pressure as movement past the connecting hole would reduce small channel pressure. That reduced pressure would draw on the mab.

* mab air would then be directed down the side channel and through the connecting orifice as a metering block style e-bleed and perform the same function as those metering block e-bleeds at higher flows.