It would SEEM to be, but reality and theory sometimes clash over tiny details.

Cases are known where turbulence, or very local pressure-build up due airflow under cowls, disturbed the proper functioning of pressure regulators on Walbro/Tillotson style carbs, necessitating attaching a pressure tube to the sensing hole, conducted to a place with more consistent pressure.
Our pressure sensors are quite a bit more sensitive than those membranes.

Admittedly, I have not yet experimented too much with that. But that kind of experimenting, because of the low sample number of 1 or 2 (I do not build THAT many new planes, or I would not have time to fly them :D ), the outcome of such experiment would not be very conclusive.

Just out of caution, I would simply not want a single unit, but something with a bit more liberty to (re)arrange things if it would turn out to be necessary.

That way, anyone would be completely free to place the sensor where it suits them, and that includes "under the cowl"...

If the sensor works just as good inside the fuse as in the cowl, I will certainly mount them in the fuse (shrink wrapped with the controller wiring). Mounting it to the firewall inside the cowl actually complicates things, as connectorizing the sensor wires and hard mounting seems almost unavoidable.

The pressure part usually works without problems, a fuse rarely is airtight and/or "pressurized". It's the temperature thing that is a bit more tricky: A plane parked in the sun CAN get warm inside, and cool down only very slow if ventilation is limited.
Heat under the cowl in general is not the problem, because whatever temperature measured, is in general related to the ambient temperature (an X amount of degrees above).

I tend to place the press/temp sensor for that reason on a well-ventilated place, shielded from direct exposure to sun. This CAN be under the cowl, but preferrably either on the belly, outside under the main wing or for example a plane with an open cockpit, in that cockpit, or behind a scale detail like a windscoop or other ventilation opening.

Whatever the case, I prefer the freedom to place it where I see fit, instead of being "locked" into placing it where the solenoid unit is.

Some success!
I went back to trying to sort my Zama electronic carb on my well proven little converted 26 cc industrial engine.
I first tried it by driving the solenoid and it's little driver with the S2 potentiometer using my RadioMaster RM16S and OpenTx.
I got it to fire and run with the pot at around 50%, which approximately concurs with the published suggested curve.
In this configuration, it actually prop hand started, which it would not do before. This is very promising!
I now have Otx set up to drive Channel 5 (solenoid channel) via a mix line from the throttle channel, as has been long since suggested.
I have only just started to adjust the curve, but I'll have to work on that and go back and read any relevant posts.
I'm aware that I can see the stick % on a page in Otx, but not at the same time as adjusting a corresponding point on the curve.
How many points should I choose to start with?
Needless to say, I am very pleased with this beginning.

Jim.

Further to my post above, I have an idea that might work in Otx.
It is likely possible to set up a logical switch to switch the throttle through 7, 9 or more stepped points. In other words, make it possible to switch in the throttle stick, or to choose the switch for adjustment purposed.
These points would be chosen to correlate with each respective point on the curve.
That way, it would be a positive and accurate way to do the adjustment to the points.
I would have to seek advice and guidance for this over on the Otx forums.
If I try to figure it out, it will take forever!
More later.

Edit:
I may be overthinking this. I filled the tank and ran the engine again and did some rough tweaking.
Short story; I was starting to get a feel for cause and effect of the curve adjustments and by the time I quit due to darkness, I had the engine idling and running throughout the throttle range fairly well. I seem to recall that some delay in the throttle is required, but that can be easily fixed in Otx.
When the engine starved at the high end, I increased 2 or 3 points on the right of the curve (to richen) and when it would not idle, I did the reverse, lowered the points on the left end (to lean it out), and that appears to be getting the tune closer to what is required.
Rough and approximate only, but it has me started on the process to get it running well. I will do some more careful tuning next session.
I was able to hand prop start it a few times; it would not do so on the old diaphragm carb!

Jim.

Check if there is an indexing on your gimbal.
My own TX has a 9-stripe index, so I use 9 pointed curves for both throttle curve and mixture curve.
I link both channels to the stick, which makes each point on the curve correspond with its own index mark on the gimbal.

The throttle curve should be set once, like a progressive curve, and preferrably NOT be modified unless really really necessary. Ideally, you want an as linear as possible stickposition-RPM relation.
Especially pumpercarbs like the ZAMA and Walbro, they are horribly non-linear in their RPM response. With minimum throttle being idle and full throttle of course WOT, you want something like 1/4th stick corresponding with about 10% of servo (and butterfly valve) travel, 1/2 stick approx 25% servo travel and 3/4 stick 50~60% in order to have that RPM linearity.

If your gimbal has less indexes, like 7 or even 5, you MIGHT suffer from the curve being too coarse if only using the same number of points as your index, in that case, take a curve with ( 2 x index minus 1). For an index with 7 marks that would be 13 points, for an index with 5 marks, that would be 9. That will bring the additional points exactly in the middle between the indexes.

Having set it up like that, you can run the engine, move the throttle, observe if there are any lean or rich patches, and very easily visually identify WHERE on the curve that point is.
This even goes for in-flight. When you observe a rich or lean spot, a quick glance will tell you which point to adjust. Land, adjust, try again.

Crude adjustments, you can make in relatively rapid succession, but those really minute "finetunings", give the engine time to "settle" because since mixture changes affect oil properties, a minor adjustment takes some runtime to take hold.

That sounds promising!

I think I mentioned, that there was some "getting a feel for it" involved, and I am very happy to see, you managed to aquire that.

Trust me, this will grow on you, and there will be a time where you wondered how you ever managed with only the "H" and "L" screws... ;)

As to your question on the set-up with the switch, I have never been able to figure out a programming in Open TX that would allow me to tune the mixture "on the fly" in flight.
If I understand you correct, you want to have some sort of programming that automatically assigns one single pot to a different point on the curve, that point depending on the actual throttle position?
I really have no idea whether OpenTX would allow something like that. IF so, then at least via LUA script, but I have no real experience with that.

What I DO know however, is that "a slightly rich curve is a safe mixture" and a "perfect" curve can only be sneaked up on in flight.
My recommendation: once you trust your engine's behaviour sufficient for flight, just go fly. Sooner or later, getting more and more familiar with engine/plane combo, rich spots and lean spots will start to stand out.
Identify the throttle position that has that spot, land, adjust 1 or 2 % and see whether it is solved.
In case of doubt, ALWAYS first go richer. If that worsens the hickup, you know which way to go and how much without risking a flame-out and deadstick landing.

And as said in previous post: the crude adjustments are not the issue, but the fine tuning, do NOT rush it. Give it time, let the engine settle.
I never do more than one "minor correction" per outing, then fly it like that for the rest of the day.
Make a habit of checking your exhaust residue at the end of each day, the cleaner it gets, the closer you are to "perfect", and with this set-up it actually IS possible to achieve a virtually non-black exhaust residue. It's NOT a necessity (a little bit blackish crud does NOT indicate a problem of any kind), just that when it turns to brown and "recognizable as oil" that means you are darn close to perfect.

There is no mechanical indexing on my RadioMaster RM16S

I have no throttle curve in the set up...yet. Mainly due to my infinite ignorance. I will go back over the huge thread and find posts describing how to establish one.

There is some mis-communication here. I may have asked that question last year some time, but that has been resolved in the negative as far as I know. My use of pot S2 (to operate the solenoid driver directly) yesterday for the first successful startup was only very temporary to confirm the engine would fire up and run in the very first instance. I recall you describing this earlier on. Temporary measure only.

Excellent! Well noted. The exhaust is dirty black currently.........for reasons that will be obvious.

Many thanks once again for you detailed reply Bert!
I have some way to go yet, but I'm confident now that I/we can get it sorted out to operate real nice.

Jim.
https://cimg0.ibsrv.net/gimg/www.rcu...8cb7bad5f1.png
This is the curve that I have operational at present.

I have received generous assistance over on the Otx. forum on rcgroups overnight.
It does appear that there is a very simple way to create a stepped curve to switch the throttle sequentially through pre-set points. At this early stage, it appears that this will suit the purpose of adjusting the solenoid driver curve accurately at each chosen point.
More about that later, I have only just read the post describing it.

For some unknown reason, I am unable to upload an .otx file. Error notice: unacceptable file type.
(I thought some Otx user might be interested in looking at it.).

Jim.

Ok? That's too bad, because that would really help with setting up.
Maybe there is a way to improvise one? Like simply sticking some 1 mm grid paper to the side of the throttle stick?
Just rattling off something off the back of my mind?

No need to go over the entire thread...
Here's how to do it: Provided the mechanical linkage between servo and throttle lever is 1:1, linear and symetric, the following curve will yield very acceptable results:
(9 point curve)
-100, -90, -75, -55, -20, +20, +50, +75, +100.

Use "smooth" function, and if needed, modify to suit

Without the throttle curve your engine will allready be well above the middle of the practical RPM range with less than 1/4 stick.
The issue is not so much "controllability of the engine" itself (which, I can assure you, REALLY helps to grease those landings once you're used to it), but it is that in that low throttle range, mixture requirements are fairly critical. If you use a linear throttle curve, assuming 9 point curves, there is only 2 points on the mixture-curve to cover well over half the usable RPM range, which simply is not enough to cover that wide a range. Then you have 6 points to cover a MUCH smaller RPM difference, and there is no need OR use for that much resolution in a rather uncritical part of the carburation.
The purpose of the throttle curve, is to "spread the RPM spectrum out" in a linear fashion over the entire stickrange. Doing that, now you have FOUR points covering a smaller RPM range, which will allow a much better control, and you will be rewarded with a very smooth engine response.

PS: that curve looks pretty decent for a linear throttle set-up.
Notice, that your fuel curve is steep off idle and flattens out towards full throttle.
A progressive throttle curve will cause your fuel curve to be steep at the high end and flatter at the low end, allowing for finer fuel control, and a cleaner exhaust residue, which, while absolutely NOT a critical thing to have, I am sure anyone can appreciate cleaner planes. Makes it easier to justify the hobby to one's significant others :D :D :D

Excellent! I understand all that and it makes good logical sense.
I will report back with news in a day or so.
Thanks again Bert.

Jim.

Jim,

Great to hear of your success.. This is a system that really has an "operational" learning curve. Once you have one operating well enough to run reliably then just playing with it and experimenting with small changes builds the reactionary knowledge needed and success is much easier on subsequent tries. It's sometimes difficult to convey this type of experience "in words" to help people along, but you have gotten over the threshold.

The one item I took the longest to learn is the rich/lean reaction of an engine that's well tuned.. the old twin needle carb setups are rarely well tuned but once your able to really tune the mix well the "dead spot" in the middle can offer some issues until you figure out how to recognize it. this becomes a bit more pronounced once airborne and that is why Bert recommends being on the "richer side". With some practice you will note a band in the middle of each mixture point where nothing really changes. I aim for the rich side of this point on initial setups knowing that the ideal might be a bit farther lean but this is the safer starting point. The "too lean" condition with this system is not as pronounced as we are use to.. if pushed the engine just quits as a normal lean condition but it starts as "throttle hesitation" and a "bit of surging" and sometimes random shutoffs when seemingly running well..

This, indeed, is an issue to take into consideration.
For ANY given throttle position, there are three very distinct mixture areas: Too rich, when leaning that out, you will encounter that "dead zone", a relatively small area where changes in mixture do not seem to make much difference, and then an even narrower "lean range" where the engine is VERY prone to cutting out, but most of the time still is able to sustain running.

IN FLIGHT, on the very edge between the dead zone and the lean range, audibly the engine CAN seem to run rich: it starts to misfire occasionally and runs a bit irregular. You will not be able to hit this spot on the bench, but in flight I have seen it several times. This is because of the effects of airspeed acting on the propeller's RPM/load curve. Explaining that would take a bit of time and text.

Those zones, especially the flat "dead zone" is why I recommend to look for the rich side of that dead zone.
The phenomenon of an engine that ACTUALLY runs lean, but CAN give the audible impression of still running rich, is why I ALWAYS recommend that, when a spot on the curve is identified that needs correction, ALWAYS FIRST go rich, in order to verify whether that improves or deteriorates the situation. Simply because while any RC pilot should be able to handle a deadstick, any deadstick DOES present a risk, and should be avoided if possible.
From this also can be concluded: ANY deadstick, if not caused by a technical or electr(on)ic fallure, IS caused by a lean situation. Rich mixtured do not flame out. Ask any PPL holder what is on the checklist for landing and why.

Thanks for the reply Chris; good to hear from you.

I have already become aware of this in my approximate tuning efforts to date.

I plan to incorporate the stepped throttle curve in my Otx set up for this carb/model.
If all goes to plan, it will help considerably with tuning at each point of throttle opening.

Jim.

Please keep us informed.
We can learn from EVERY relevant experience, and in this case, any data on alternative ways to achieve a good tuning can help others.
There are more ways to skin a cat and we want to learn about all of them :D

By the way, does your TX have a logging function?
With relatively simple telemetry (RPM and MAYBE CHT) and a logging function, it becomes easier to determine the lean points by reviewing flights and identifying throttle position in relation to RPM and or flame-out points.

For example, the RPM following the throttle on the ground but not in the air (RPM hesitant to drop when throttle is reduced to idle) can be indicative of a too rich idle. That kind of thing.

I used to use log-review fairly intensive, for learning purposes. It gives great insight in what is actually happening. Nowadays, based on that insight, I can mainly go by gutfeel but in the early days telemetry and logfile review were an invaluable tool to me.

Short video of engine running.
 

The tune has yet to be done via the instructions........for a number of reasons. I am still working towards that. I still have some questions around that, but I need to clarify my thoughts further before asking.
In the meantime, this is a video of the engine running with a rough "seat of the pants" kind of adjustment of the solenoid drive curve.

https://vimeo.com/manage/videos/1094268392

I will be interested in some assessment about what is happening in the RPM range just above idle. Is this rich or lean?

I cannot watch that video without getting me a Vimeo account, apparently.
Is it possible to post it in a public format?

Sorry Bert, but I don't know what you mean. What is an example of a "public format".
Vimeo is about as "public" as it gets, to the best of my knowledge.
Let me see:
List of other video hosting platforms include:
*****ute
Rumble
Youtube
etc.
Which is your preference? Is there a problem in getting a Vimeo account? I seem to recall that you have viewed one of my videos on Vimeo before.

Matching throttle output to each successive point on the curve.
 

I plan to experiment on an alternative way to do this.
In Otx. 2.3.15
If I select "fixed X" in the parameters entry in the curved set up page, then each of the nine points will be separated by 12.5% of the 500 uS between max and min throttle stick positions.........(My channel output displaying 1500 to 2000 when the stick is moved from min to max.)
I simply need do a quick bit arithmetic and make a list of the 9 positions value in mS.
That is:
1500 1562 1625 1749 1812 1874 1740 1937 2000
Then set the throttle on each figure as displayed on the RadioMaster RM 16S tx. channel outputs page, and then adjust the corresponding point on the curve..

I plan to try this tomorrow and improve my solenoid tuning skills!

Jim.

My terminology probably isn't the best... I think I meant "embedded"...

As it is, that link directs me to Vimeo in such a way, that I have to create an account in order to be able to view it. A bit the equivalent of a paywall, I guess.
I have always been able to watch YT also without having to have an account of my own, and I distinctly remember having seen Vimeo vids (both in general as well as yours) before, so I am actually very surprised that in this case this particular link won't allow me to.
I am not "internet whizz kid" enough to explain it any better.

I do not want to get an account, because I am slightly autistic, and all these accounts and stuff tend to clutter my brain, my computer, and cause confusion in my head.

I understand Bert, I will see if I can sort out an alternative. I also don't want to establish a youtube account for somewhat similar reasons. There is too much funny / controversial stuff around the policy and conditions that they require.
It appears that Vimeo has changed their policy.

Jim.

Jim,

I don't use stepped throttle or a mechanically indexed throttle to determine throttle position while using otx. I simply set up a momementary switch to play an audible throttle position in flight. Adjustments are then accomplished on the ground at the same throttle position. Can't get any more simple or accurate than that.

Very good suggestion. I will try that tomorrow.
Thanks.

Now dammit! THAT is a clever solution!

And stuff like this, is what makes this forum so valuable! Thanks!

Jim,
Looks (sounds) like your off to a good start... I was able to watch the video straight up without a log in process

Love the Throttle position call out idea - That's a keeper...

Chris