Actually, it IS completely and 100% impossible, because the airbleed hole is closed off at just a touch above idle. So idle adjustment does not affect midrange, and the main needle is a fixed setting for the remaining throttle range.

Really, it will not work. Period. The engine will run, and it might even be possible to fly with it, but engine behaviour will be marginal and barely acceptable.

Not to be confused with Chris' servo-operated airbleed adjustment, which is an entirely different principle, because that form of airbleed mixture adjustment is active over the entire throttle range, AND continuous adjustable.

Throttle to air bleed valve mix. Servo on left is the throttle. Servo on right controls the drill bit moving back and forth in the air valve which will lean the mixture introduced by the carb.

Bert. Will Chris’s air bleed system work with an air bleed carb? You could shut off the carb’s air bleed screw and use Chris’s system.

xanaphyst. I believe you are correct that the hall sensor circuit is 5 volts and would need to be reduced to 3.3volts.

Do that with any small switching transistor and a pair of resistors.

2n3904 would do this easily.

But you need to introduce the regulated bleed air between the carburetor and the crankshaft right?
On the fp the only way i can think off to do that is to remove one of the carb mounting screws and replace it with a pressure nipple.
Finding one that has the same size (m3?) that you can screw in the screw location might be complicated.

On the fp airbleed style carb does the rotating barrel move in and out of the carb case?
Or is the slot that keeps the barrel in place cut exacly 90 degrees to the barrel ?

effect of the main needle
 

So the main needle of a air bleed style carb influences the mixture over the whole throttle range including idle?

Did not have to change the air bleed setting of any of my fp engines in years so forgot how the carbs react.

Yes, and I believe I closed the air bleed entirely because I couldn't get a good mixture curve tuned with it open, probably because of that abrupt mixture change when it closes.

guess i have some testing to do
 

Because of the experiences with the carbsmart i wonder if a a servo actuated main needle can replace the solenoid or external bleed air systems.
How valid would a test result be of a engine running on glow fuel .with a closed air bleed screw?

Also just have a thought if a inductor mounted in the backplate could detect the crankpin passing.
The generated voltage "straight" probably would be far to low but might be enough to trigger a fet (possible with a zener across the inductor to avoid problems at higher rpm/)
If that could be made to work then that would eliminate the need to mount a magnet and hall sensor.
And reading the crankpin position would make setup trivial

You won't have enough resolution to tune the engine by controlling the needle. Backplate hall rpm sensors are available. They're used on gas/nitro helicopters for the governor. You'd still need a way to adjust timing.

An airbleed carb is an extremely simplistic configuration, that has a single needle and spraybar, without ANY additional form of fuel metering when the throttle is closed.
Fuel draw reduces when the throttle is closed as a matter of "duh" but it is in no way shape or form linear to the air throughput. Full throttle mixture is set by means of the main needle, and fuel/air ration "is what it is, whatever it may be" in all other throttle positions.
At really low throttle positions, this mixture will be extremely rich, and that is where the airbleed opens (at approx 1/4 of throttle opening, aka when the throttle is nearly closed) but from 1/4 to full, no other form of fuel metering is active.

Yes... provided proper dimensioning of the additional air bleed channel, that would work.

Airbleed carbs usually have a slot at 90 degrees to the barrel.

Indeed, the best way is to introduce the bleed air between carb and crankshaft port, by replacing that schrew with a nipple, If done carefully, the corresponding holes can be drilled/retapped for M4 if necessary, a .60 should have ample room for that.

Nipples are availlable in M3, M3,5 and M4 as standard sizes at least and probably also in imperial sizes

:D guilty...

Unless you design and fabricate a high precision NVA set-up, no servo-adjustable needle valve has the required precision.

Many years ago I worked on a backplate mounted crankpin sensor to trigger the ignition in my helicopters. The Hall sensor used is MLX90217. It required a magnet fixed to the sensor, and the sensor responded to the passing crankpin distorting the fieldlines of the magnetic field. It worked well, and I have built at least 20 or so of those sensors for others, some are still in use after at least 15 years.
That same sensor can, of course, also trigger a tach, but to be honest, a bit overdone for only that purpose, since it has sufficient accuracy for triggering an ignition.

It worked well, but was a bit tricky to set up: it required milling the backplate down in order to achieve an acceptable passing distance between sensor, and setting the timing required quite a bit of attention as the spacial adjustment was extremely tiny movements.
Here it is initially with an OS engine, still running methanol but allready on spark ignition.
That OS self-destructed due to the use of castor "glueing in" the wristpin.
It was replaced with an ASP 36...

Come to think of it... It was exactly THIS helicopter due to its rather imperfect ASP carb, that inspired me to start investigating the possibilities for electronic mixture control....

Funny how things sometimes coincidentally come full circle... :D

The discussion has been very interesting. Yes my OS carb’s barrel doesn’t move in or out. It does have the two mounting screws and I have some M3 nipples on their way. Chris made that set up look simple. I have other carbs that don’t have the same mountings screws and I figured I would just drill a hole and tap it. I’m aware of eliminating any other air leaks around the carb so I will pay attention to that. Somehow I think having the needle set to one opening and then controlling the air flow would almost be better than a carb with a moving barrel. I guess I’ll find out. I imagine the critical part for the idle is if there is enough air flow to draw in the fuel.

I like the idea of controlling the needle but that raises the complexity of the process.

We really need fuel injection. 😊

I think this week I will get some time to experiment. I have an evolution 61 and Thunder Tiger Pro 60 to work with. They have the two needle carbs. It should be an interesting learning experience.

The solenoid, with either Dave's or Hans' driver (the versions compensated for atmospheric conditions), is the closest thing for reasonable money and effort.

I would agree with you on that.

why didn't you flipped it (bmp module ) reverse and resolder to have an inline configuration to put in a 3d printed box or a heashrinkable tube?

why didn't you flipped it (bmp module ) reverse and resolder to have an inline configuration to put in a 3d printed box or a heashrinkable tube?

I ran an Evolution 61 on gas today and it seemed to run well. I’m not having mid range issues with this engine or my OS 60. What rpm’s do you consider mid range. I don’t have a tach on my engines so I’m not really sure what rpm’s they are running at. I ordered a tach today so I can better understand what kind of performance I am getting. I wasn’t able to get a low idle. This engine comes with limiters on the high side needle and low side needle. I removed the limiter on the high side and will remove the low side as well. I’m thinking that these engines seem to run fine from 3500 or 4000 and up. They don’t seem to stumble when opening the throttle. None of them are on a plane yet so I can’t point the engines up and down to see what happens. The Evolution has a rear needle valve and it looks like I have an air leak from that rear valve to the front carb. I wasn’t seeing air in the line from the tank to the rear valve but I had air in the line from the rear valve to the front carb. It may be the o-ring on the needle. I ordered some o-rings so hopefully that will help. It is fun to see these engines run on gas. I need to get a plane to put these engines on to test them in the air.

A .60 2stroke should, without issues, idle at 2000 RPM or less on gasoline.

I am pretty sure, you ARE having midrange mixture issues, you most likely (and in no way meant condescending) don't know yet how to recognize them.
I know I did not recognize them back then. Again: not recognizing those midrange issues is very normal for anyone used to the sound and "feel" of a glow engine.

This is a completely unmodified engine running gasoline, and I TOO thought that it ran reasonably well...
It was sheer horror in the air with a very unpredictable and erratic throttle behaviour. All I can say is that it revved up when you gave it throttle in the air, and it revved down when you pulled back, but it was anyones guess WHEN it would respond or by how much, or whether it would hold a constant RPM.

This is the same engine, with a modified carb, by grinding the slanted groove in the throttlebarrel:
Much better. Absolutely flyable and reliable throttle response fairly direct but above all predictable.
Still far from perfect, BUT this plane is still in my posession, and to this day (now about 10 years ago) still flown in this specific set-up. Just a modified carb, no other electronic wizzardry.

And THIS is what CAN be had, when using the solenoid. Sheer perfection:
One could almost play musical scales with the throttle, and very senistive and accurate control.
This is by the way, an ASP .91 2-stroke.

Now, it does not automatically run like that just by installing a solenoid, it does take some real time flighttesting and finetuning the fuel curve, but it CAN be done.

Your "leakage problem" with the remote needle set-up is with 99,999999% certainty NOT a leakage, but heat transfer from engine block to remote NVA. In combination with the pressure drop over the metering orifice, the heat transfer causes evaporation.
Solution is extremely simple: mechanically decouple the remote NVA from the engine block, fit it against the engine bay firewall or something like that.

Howdy Gents,

Would anyone happen to have the injector housing in STP, STEP, DWG, or DXF file format?

Thank You,

Xanaphyst

Your comments were exactly what I needed. Unfortunately I don’t have a lot of nitro engine experience. I flew a few of the 25 years ago but recently it’s electric or gas engines. So listening to the engines on the bench makes me think I can just mount them on a plane. Any suggestions on why I’m not getting a decent idle from one engine with an air bleed carb and the other with a two needle carb? I did retard my spark a little yesterday and the two needle engine had a better idle. I was expecting that.

Thanks for the tip about the remote needle. That makes sense.

If my engines run pretty well without mods is it easy to tell the difference when adding let’s say the air bleed device? Will I recognize the difference immediately? I should have my nipples in a few days. Then I can set up an air bleed device and see how things behave.

Thanks for your advice. I really appreciate the help.

I moved the remote needle, took off the limiter on the low needle and then did my best to tune the Evolution 61. I got a tachometer and my top end was 10500 with a 13x6 prop. I couldn’t get a good idle. Once I’m below 3000 it may run for a while but it always sounds like it is going to die. I found a low needle setting that enabled the engine to run and then as the throttle closed more the rpm’s increased. I figured I was at the lean end of that adjustment. When I opened the low needle an 1/8 of a turn that throttle increase went away but my idle was erratic and in the high 2000 or at 3000. I seem to be at an impasse. Any suggestions to get a lower idle would be appreciated.