Racing Fuel Systems

I've seen several talking about converting SMAB carbs to the traditional DMAB set-up. For those of you that have done this modification on a well-sorted SMAB carb, have you seen any noticeable improvement in part throttle A/F behavior? Is it worth doing? I'm mainly looking for more stable A/F at cruise, as my SMAB carb works great but tends to trend rich with RPM at light loads.

They haven't made the journey yet.

Hi
All the Qjets ,I have tuned are DMAB ,picked these at swap meets here in Oz ,
all from GM Holden V8's.
I can say these carbs go leaner til the power piston is released .
I know this doesn't answer your question ,but something to add
to the Qjet file.

Tuner: Thanks for your input. To answer some of your questions:

Idle circuit:

Lower IAB: 0.059"
Upper IAB: 0.067"
Idle DCR: 0.052"
IFR (tube): 0.035"
Idle bypass air: 0.072"

This is pretty much "as delivered" for this particular SMAB carb, though I did reduce the Idle air bypass a bit.

When I say "trends rich", here is a better description. Not necessarily constant load... level road surface, high gear. Runs good with A/F at 16:1 @ 50 mph (arbitrary example), but will trend to 14.7:1 @ 80 mph. Load obviously increases with speed, but level road is still light load, and not enough to raise to the power piston and get into power enrichment. I haven't actually had a vacuum gauge on it, but I am assuming based on pedal position that vacuum is not dropping a bunch under these conditions, and I don't have a heavy power piston spring.

I am pondering how to flatten that part of the load vs A/F curve.

What size is the single main bleed above the nozzle? What is the difference in intake vacuum at 50 and 80 MPH.

Yer gonna have to build up one of those Hybrids like I did & try.

Might have gotten a bit better MPG. I relocated the upper idle bleed too, so I think the light 30-40 mph cruise is a bit better.