That would not work, since the "weather-compensation" with the solenoid, adjusts fuel admission over the entire range exactly to proportion, which is pretty simple using a dutycycle-modulated valve for the fuel only, and a (mechanically constant) single air throttle... Very crudely spoken: assuming a baseline value, the the CHANGE in density of the air is calculated, and fuel is admitted more, or less, in accordance. That is very easy to do because the fuel needle determines a flowrate, and the solenoid LINEARLY increases or decreases fuel flow, regardless of needle setting. Within the range we see it, and liquids not being compressible, volume-flow is directly related to massflow

But to have a fixed fuel supply and TWO air throttles, becomes a nightmare to compensate for the weather. Suddenly you need to have info on the ratio between direct air and bleed air (you need to have throttle position sensors on BOTH throttle and bleedvalve), in order to work out how much the bleedvalve has to be opened to effect the change in airflow in order to keep fuel/air ratio constant, because for air, given the pressure differences over the throttles and gasses being compressible, the relation between volume flow and massflow of the air is, to put it mildly, "a bit flexible".

I would most definitely NOT advise to go that way.

The air bleed system will work, as long as you check the main needle setting before flight, and it MIGHT require a retune of the idle needle setting IF the last previous flight was in very different circumstances.

The solenoid system simply works, period, with the only periodical changes to the needle setting originating from imperfections in the correction factor.
What I have seen, that limits itself to one click richer or leaner between winter and summer (western European North Sea climate).
Occasionally, I have to, what I call, "flush the needle". That is when the engine runs lean despite NO weather change, but as soon as the needle is opened one or two clicks, it immediately becomes rich again and I have to return the needle back to its initial setting within 10 seconds or so. I guess no matter how much fuel is filtered, due to the evaporation going on in the carb, miniscule deposits WILL happen...

I’ll have to admit that the solinoid is a bit smaller than I had imagined 😳

Yup... it is proven small enough to be used on .30 fourstroke engines. And it can provenhandle all the way up to 4. cu.in. engines. Pretty versatile if you ask me...

I have been following this thread with interest. I have been wanting to convert nitro engines to gas for sometime. I recently came into a large amount of Nitro engines. 2 strokes and 4 strokes. I was contemplating the pursuit of using walbro carbs on the larger engines. I may still try that but the air bleed control is a brilliant solution to the problems of using the standard carbs on the nitro engine. It works just like an idle air control valve, (IAC) on a car. The IAC on a car operates off a stepping motor that opens and closes an air bypass passage around the throttle plate. I'm not suggesting going that route but when I read about the air bleed control it hit me as an easy way to adjust the air to fuel ratio for these engines. I'm a ways away from doing this myself but I have a Magnum 91 that sounds like a good start. Thank you all for sharing your information. I have been working on electronic ignitions for converted weed wackers. I have used the cheap Chinese scooter ignition systems but recently have been using a Stirling Kit CDI that sells for $20. I have not had a failure with that system. It doesn't have a built in timing curve but I have been getting really good performance from my engines using it and setting timing at close to 28 degrees BTDC for the 2 strokes. CDI systems probably would be on another thread but if anyone is interested in my system let me know.

Today I gave the Saito 72 its first run on gas. I probably should have ran it hard on glow fuel for a few min to get it warmed up and the old oil blown out. It also has new bearings that aren’t broken in. The initial start and run was tough to get settled in but it has cleaned up a lot now. It runs better and better as it builds time.


I can’t believe how clean the exhaust is. No smoke and no nasty oil slick !!!

Transition is pretty rough as expected.

Now I just need to figure out my injector housing solution.

Which fuel/oil ratio are you running?

Xanaphyst, Bernett and everyone else currently active on this thread,

I have not done anything related to RC in years and will no longer be pursuing the hobby. Point is, I have several complete solenoid systems that I will send to whomever would like them for the cost of shipping.

I would love to have those and can pay above shipping as well !! Nb

20-1

Stihl HP Ultra full synthetic

I've had every intention of building one of these for the last couple years (and acquired some of the parts too) but haven't gotten around to it, what with a toddler and all. If you've got a spare I'd be happy to take one.

I was thinking about the air bleed system and I believe someone could develop an electronic control system that would automatically adjust the air bleed valve to meet the specs programmed for an engine. Sort of like an electronic fuel injection system but basically an air injection system. We know the throttle position from the servo, we know the rpms from the electronic ignition and we can program an ideal rpm curve based on the throttle position. Then a microprocessor adjusts the air by the air bleed valve to get the engine to run at the correct rpm per the throttle servo inputs. You probably would need to dial that in for each engine but once you had done a few it may not be that difficult. There may be some hunting/ surging happening as the microprocessor makes adjustments and keeps trying to keep the rpms matched to the program. It's just an idea.

I was thinking the same thing but then brutus pointed out the DUAL AIR ratio issue at idle and wide open. Too much effort for the reward ratio at that point.

I'm not sure of the DUAL AIR ratio issue? Can you please explain that? Thanks

Deleted..

post 2776

That is about the leanest I would go... Personally, I prefer 10:1 for anything below 15 cc (.9 cu.in) per cylinder, and 15:1 for anything above that, meaning that I run my 1.6 cu in boxer and 4 cu.in. radial still on 10:1 but would run a 1.2 cu.in. single on 15:1

I am aware that 20:1 will not immediately wreck an engine and some manufacturers like Saito APPEAR to recommend it (if you read their manual carefully, they state that to be the limit for reasons of warranty, hinting at more oil being beneficially), but I have never seen an advantage of going leaner than15:1...

Sad to see you leave the hobby, Lonnie, but a big thumbs up for making your solenoid systems availlable to others!

I read the post about the dual air ratio issue. Thanks. I think having a microprocessor involved in controlling the air bleed system would be better than the present system to accommodate for changes in atmospheric pressure. I'm pretty sure the existing system would be fine in most circumstances but may require tweaking at times. If you program a microprocessor to achieve desired rpms at certain points in the throttle curve it would achieve that by adjusting the air bleed system and it should be able to make up for changes in atmospheric pressure. I'm not saying it would be easy to do but doable. You would need to have the program avoid an overly lean condition to prevent dead sticks. If you said you wanted your top end to be 7,000 rpms and the microprocessor keeps leaning out the mixture trying to achieve that it could create an overly lean condition. I did discover that you can obtain the rpms from a CDI by attaching a Y cable to the hall sensor. That should be a way of connecting a microprocessor to read the rpms of the engine. I appreciate the offer for the solenoids but I will let others pursue that route. It is a generous offer.

Sounds like a good plan. I’ll revise my ratio per your ideas.

thank you !!

A road of small victories eventually lead to success !!

I can, from experience, assure that sure, you WILL get some oil back on the plane compared to 20:1, but nowhere near comparable to what you see on glow. The difference is still "staggering".

That oil, by the way, is an excellent indicator for both the internal condition of your engine (if you know how to do a paper-chromatography with the crankcase effluent, it is easy to keep track of state of break-in, wear particles etc etc) as well as a very good indicator of "hitting the perfect stoichiometry".
A rich engine expells dark or black oil from the exhaust (and THUS also from the crankcase) and by the time you see that residue clear up, that's where you are touching on the sweet spot. Mind you, you will NOT see the colour of the effluent change with turning the needle. A change in mixture will take several flights to take effect, so it really is a matter of "sneaking up onto the perfect setting". Do not rush it. Both the needles as well as the curve, once it is flyable, make SMALL changes, and give each change TIME.

I run all my engines on 10:1 (for reason of not having anything above .90 cu.in per cylinder) but 15:1 WILL run any smaller engine just as well. I tested that with a .52 fourstroke, and I could not detect any negative effects.
I simply did not like the "dry feel" of the engine when turning over by hand in the hobby basement, that's all. I could not detect any significant difference in running temperature, power or anything. I simply like to err on the safe side...

10:1 or 15:1 (or perhaps your own ratio of your liking, that really is a matter of preference), but one thing I can recommend: once you figured out what ratio you prefer for your particular set of circumstances, STICK WITH IT, as accurately as you can. A consistent ratio absolutely helps for consistent running. Mixing small batches, makes accurate and consistent mixing more difficult.
Good 2-stroke oils stabilize the gasoline, and I usually mix a batch of approx 3 gallon (11 litres to be exact, 10 Litres of gas on 1 litre of oil. Consistency, remember? ). I have never had ANY issues with gas getting stale this way. Since on your side of the pond they sell gas in gallons and oil in quarts, 12:1 or 16:1 for example would also be perfectly convenient ratios with very accurate repeatability.
IF I would be in the states, I'd probably use one of those ratios.

xanaphyst. What am I looking at in your latest post? I'm definitely interested in what you are doing. Thanks

I have another thought for the group. Going back to Cat1's air bleed set up and having the servo controlled on another curve. I'm not that sophisticated with programming transmitters but I will become better. My thought is can you "mix" another channel to control the entire curve by using a slider or rotating knob? If you can do that then you could easily tweak the air mixture at the field to optimize for any atmospheric changes. My ignorance of programming transmitters is probably showing but I know that on gyros your can adjust the gain of throws during actual flight with that channel set to a slider or rotating knob. I would think you would want to adjust the entire curve and not just one point on the curve if there was an atmospheric change in conditions that warranted some tweaking to optimize engine performance. Am I making sense?

Sorry for the repeated posts. I answered my earlier question about programming a transmitter to be able to move an entire curve using another channel. I asked Gemini the question. I have a radipmaster Tx16s transmitter. I think it may be an easier way to change your curve depending on atmosheric conditions or even different engines. Although I suspect for each engine you would need a specific curve. Here is the replay I received from Gemini..

Gemini said

Yes, you can absolutely do this. In EdgeTX (the operating system on your TX16S), this is a classic "Master-Slave" mixing scenario. You will use the Mixes screen to link the second servo to your throttle and a Global Variable (GV) or Offset to allow a third channel (like a knob or slider) to shift that servo's position.

Here is how to set it up step-by-step:

1. Create a Custom Throttle Curve

Before mixing, you need the "different throttle curve" for your second servo.

• Go to the Curves page in your Model Menu.
  
• Select Curve 1 (or any empty curve) and name it something like
  Code:

  Thr2

  .
  
• Set the points to define how you want the second servo to behave relative to the throttle stick.
  

2. Link the Second Servo to Throttle

Now, you’ll tell the second servo to follow the throttle stick but use your new curve.

• Go to the Mixes page.
  
• Find an empty channel (e.g., CH5) for your second servo.
  
• Create a new Mix:
  
  • Source:
    Code:

    Thr

    (Throttle Stick)
    
  • Curve:
    Code:

    Cstm

    -> Select your
    Code:

    Thr2

    curve.
    
  • Weight:
    Code:

    100%

    (adjust if you need to limit the total throw later).
    

3. Add Control from a Third Channel (The Offset)

To control the "entire curve position" (shifting the whole range up or down) using a third channel (e.g., the S1 or S2 knob):

• On the same channel you just created (CH5), add a second mix line below the first one.
  
• Source: Select your knob (e.g.,
  Code:

  S1

  ).
  
• Multiplex: Set this to Add.
  
• Weight: Start with
  Code:

  20%

  or
  Code:

  50%

  . This determines how much "shifting" the knob can actually do. If it's too sensitive, lower this number.
  

How it Works in Flight

• Throttle Stick: Moves both servos. The first follows the standard throttle, the second follows your custom
  Code:

  Thr2

  curve.
  
• Knob (S1): Acts as a "sliding offset." As you turn it, it will shift the second servo's entire movement range up or down without changing the shape of the curve you designed.
  

Pro-Tip: Avoid Servo Binding

Since you are adding an offset on top of a curve, it is possible to "over-drive" the servo beyond its physical limits.

• Go to the Outputs page for CH5.
  
• Set the Min and Max limits strictly so the servo doesn't hit a mechanical stop and burn out while you are adjusting the knob at full throttle.
  

Would you like me to explain how to make the third channel only active when a specific switch is flipped?
.

For the solenoid, that is an option, PROVIDED you set up the knob such that it "amplifies" the fuel curve, not just lowers and raises it by a few points.
I have tested that (in my particular transmitter, setting the program up to amplify instead of lower/raise comes at the expense of resolution, but it does work. It is not very useful, because it prerequires a properly set up curve to begin with, and it does exactly the same as opening or closing the main needle a bit.
But basically, that is what the "atmospheric compensation" allready does via the BMP280. Automatically, and more important, immediately and to exact "local conditions".

In theory, your idea works, and I applied it prior to Dave (Taylor) coming up with the idea of fitting a pressure/temp sensor and do it automatically.
Pre-"knob", I simply tuned the needle, and all three methods work. Post-"knob" I simply "tuned" the engine via the transmitter.
Post-sensor I did not have to do anything anymore, basically.
The sensor has the advantage of ALSO compensating for flight altitude, and I can assure you, that that difference is VERY noticable, if you know what to look for.
Prior to the sensor, I could have the cleanest, leanest running engines on the ground, with perfectly clean exhaust residue, but after a flight the residue would be black. This because the air density decreases at altitude, but the fuel supply remains by&large the same. After installing the sensor, that residue remained clean, regardless of how high I went.

A knob won't do that for you.