Feedback carburetor -- revisited and modernized

It's working in closed loop pretty well now. I need to clean up the web page, I'll do that shortly.

It's a funny system. The carb does the hard work of doling out fuel, but the electronics trims down all the stuff you wish you could get at jetting in the usual way.

The center of the fuel map, where you spend most of your time cruising, can get really detailed tunings. Super-light throttle 60 mph cruise I can stretch it out to 16:1 AFR, and have it immediately enrich to 14.7 for moderate highway load, just 10 or 20 KPa higher, and hill-lugging at 13.7.

With the jet and a two-step rod, you get two ranges of light-to-moderate throttle adjustments. Now there's 50 cells worth.  I built a tuner/editor into the panel, so on a stretch of road you can throttle to a particular load/rpm spot, and touch up AFR at that one spot.

I'm thinking that on a long drive, long flat desert road type thing, I can tweak flat-cruise AFR such that manifold pressure drops (vacuum increase) for max power/mileage at that "setting" (rpm/mani pressure). Settings are saved automatically in onboard EEPROM.

It's a lot "softer" than an EFI system because there's the carb doing the main metering. The solenoid system is a bit slow to change AFR, unlike millisecond-speed injectors. But it's so nicely failsafe, and so easily tunable, I think I'll see what kind of mileage I can squeeze from it.

It would adapt to other cars pretty easily. A stepper-controlled carb would need different electronics but the control code would be the same.

In the last couple weeks I got most of the bugs out, it's routinely in use and workign great. On a recent 500 mile trip out to the Mojave desert overnight trip got 21 mpg and best of all, AFR dialed in spot-on regardless of altitude. 13.0 AFR idle above 4000 ft and sealevel. Flat and level light cruise a smooth 15.5:1, sealevel or mountains.

Web page updated.

Lol, this is not and not gonna be a popular car mod so this will be the last post probably.

Next will be to add spark control, for a Duraspark type reluctor so I can get the high advance that makes super-lean work.

Pretty slick setup! As always, tomj using his super-powers for good instead of evil.

FWIW, I was always leery of electronic ignition when it first appeared in factory cars, for the very reason Tom has explained: a screwdriver won't get you back on the road. The factory systems seem to be very reliable, as I have never been left stranded by a failure.

The aftermarkets needs to better rationalize factory cost vs reliability.

In the last month I did two more revisions of the hardware, software's much improved. On Sunday I got back from a 2000 mile trip to Santa Fe NM (from Los Angeles), mostly 5000 and up. (Route out was https://ridewithgps.com/routes/42892462, except I didn't get to Pinon AZ, 25 miles of dirt in a thunderstorm seemed foolish).)

Did some fine tuning of the AFR map and ended up getting consistently a bit over 22 MPG, a total of 10% improvement over the previous Carter YF (a '72 Gremlin carb). Totally turn-key automatic no-brainer.

Mileage quickly drops off over 15.5:1 AFR (leaner). I get lean spikes (which I'm pretty sure is misfires). But I'm running a stock distributor, the old iron one that rotates, so I have terrible spark advance control. I need to do something about that...

I might be able to bump it up a bit if I work on the spark advance. Next project...