Engine is missing when I start leaning it out?
 

I've been playing with my A/F ratio and whenever I start leaning the car out I am getting some hesitation. I believe the engine is missing (not firing) and I am not quite sure what to do. I figured I would have some knock/ping which I could deal with but I wasn't expecting this. I've already switched to a little hotter spark plug but could probably go up another couple of "heats". Any ideas?

how lean are you going? also at what load are you doing it at. light load, medium or high load.

I have heard that you can get away with leaning out the mixtures at low loads but the incoming air needs to be a certain temp too. the higher the better up to I think about 200 degrees

Depending on the engine design (swirl of cylinder contents, number of spark plugs etc) some engines have trouble running lean.

It looks like your mpg has increased nicely- you may have reached your lean limit.

Are you running high octane or regular gas?

I agree with Beef- tune it to run lean only at medium/light load- this would correspond to highway cruise, but still give you power when you need to pass someone or merge onto a freeway.

When you get to the point that, when driving on the highway, the car slows down when you press the gas pedal slightly, and then hold steady/speeds up slightly when you let up on the pedal, you are at the lean limit.

HHO should ignite easily even when lean... ;)

Make sure the ignition system is in good condition, including fresh plugs, wires and cap+ rotor if applicable. I've been able to reduce lean misfires in my car by opening the plug gap by an additional 0.01" from .028" to .038" gap. It didn't make a huge difference, where it misfired slightly now it runs cleanly.

1) I am @ 16.5:1 right now.

2) I only lean it out under light loads and certain RPMs. Right now that is when I see less than 10 on my vac gauge and I am between 2000-3000 RPM. This would be when cruising 45-55 MPH in 5th gear.

3) I am pulling air from between my radiator and the block. It should be fairly warm but with some additional piping I may be able to make it warmer. Not ready for that mod yet.

4) I've heard of people getting better mileage on a Miata with less "work" than I have done. There has to be some more MPGs I can squeeze out.

5) Regular gas

6) HHO is a joke, right? We have a $17K unit at work that produces 1L @ atmos pressure per hour. How much does a homebrew unit make? When I think of HHO all I think of is scammers selling $200 text file docs and people just talking theory. Anyone actually doing this for real (with real data to back it up)?

7) I've changed my gap from 0.037 to 0.042. Maybe I'll open it up a bit more.

I assume your vac gauge is hooked to intake manifold vacuum.

Leaning it out when the vacuum is less than 10" means you are leaning it out under heavy loads. Heavy loads= less manifold vacuum. Light loads= higher manifold vacuum.

You might try to reverse your setting so it goes lean when vacuum is above 10", leave it rich below 5" of vacuum so you will have some power when you really need it.

I meant less load than 10" on the vacuum.