1967brutus

Mind you: for lubrication it is not strictly necessary. Any decent sythetic oil will do the job.
The reason for castor is its tendency to create teflon-like deposits on the hottest parts, which will be the running surface of the piston and liner. This will basically "replace" the pistonring that these engines do not have.

mk13

Yes I understand for the effect of the castor oil like a little piston ring. Thank you!

The seal on the solenoid, it's aim to separate the inlet from the outlet of the valve, or just avoid leaking from the top of the valve?

I try a lot of things this morning, change again hose, change tank location, change position of the valve (outlet up, outlet down,...), test all the fuel line to search any leak, but nothing form me solve the bubbles problem.
I noticed when the outlet of the housing of the valve is down (toward the ground) and hose came up to the carb, I have no more micro bubbles, but every ~10s a big bubbles, like if micro bubbles agglomerate in one big bubbles.
And always no bubbles from the hose between the tank and the valve.
I'm thinking there is a micro leak but where? May be if I worn the seal during the assembly of the valve with the housing?
​​​​

1967brutus

What happens if you install the valve with the outlet to carb pointing upwards?

The microbubbles form due to cavitation, the valve opens and closes and this creates tiny shockwaves in the fuel. If the fuel has too much volatile components, this creates microbubbles.
Indeed, these can agglomerate into larger bubbles.

The O-ring seal only seals the outside of the solenoid, it is near impossible that this O-ring is leaking, but did you push the solenoid in all the way? There is a square ridge on the solenoid, and it is imperative that this ridge is in full contact with the metal of the housing..
Did you mount the solenoid with a thin smear of vaseline?

What you can do, this is a bit of a crude method, is to mix a bit of fuel, and leave the container open for half an hour (to let the most volatile components evaporate. Then test that fuel. The engine might be a bit harder to start, but should run, and chances are, this will cure the vapour issues.
Normally however, the volatile content of gasoline is tailored to the climate and the season (wintertime, gasoline is more volatile than summertime) and I have not even seen this issue in tropical climates (one of my own planes is located in Indonesia, and functions there on the local fuel exactly the same as it did in wintertime the Netherlands, did not even need to adjust the curves...)

Which exact kind of fuel are you using? E10, 98 or Alkylate fuel?

mk13

If I put the valve with the outlet up, there are continuously micro bubbles that go into the pipe and finally agglomerate into big bubbles.

Yes, I put the solenoid in the housing (contact between the square edge and the housing).
I mounted the solenoid with oil (10w40 for car engine).

I agree with your explanation about the shock wave created when the valve turns, but is it surprising that I am one of the only guys to have this problem?

I use the fuel of my lawn mower, 95E10 + 10% synthetic 2-stroke oil (I think this fuel is 3 months old)

1967brutus

The microbubbles I see in nearly all my engines. But I don't see them agglomerating into big bubbles.
If the solenoid is making hard contact with the housing, then that should be OK, especially if you used lubricant (oil is as good as vaseline, heck, a drop of spit would do the job).

The fuel should be OK, I use 95E10 as well, and my fuel jug (11 litres when mixed) easily lasts for one year or more without causing any problems, so 3 months old fuel should most definitely be OK.

I am a bit stomped here, and all I can think is to see what happens if you put a bit of fuel into an open jar for 30 minutes before filling your plane with it, just as an experiment to see whether the evaporation of the most volatile components does reduce the problem.

Meanwhile, keep working on the fuel curve, get the engine as lean as possible in the midrange. Leaner running reduces vibration.
Remember: as long as ignition timing is set properly (28 deg before TDC), it is near impossible to damage the engine with a lean run: It is not a glow engine anymore, and gassers simply stop when too lean.

mk13

Hi Bert, some new to test this morning with the 25RC and a 25LA (this engine have only 1h or 2h of running).
And same problem with each engine ☹️



​​​​​
I will try with some gasoline free of volatile components.

If after this last try nothing change, I think I will let this engine run with metanol 🫤

I don't understand why I have so much bubbles come from the valve, to the point it cut off the engine.

1967brutus

I am baffled.... I honestly am...

I mean, I have seen bubble issues before with poor tubing, or from heat, but this one I am genuinely amazed about. This does look like there is indeed a leak somewhere.

Can it be that your fuel is older than you think, and it was bought in winter time? AKA, that the fuel was formulated for colder season and contains too much volatiles?

I have checked my channel (YT) but I do not have any videos from the time I battled the same issue... I had that issue allready even before the solenoid was introduced. I have myself never really seen it since.

Please do not be too quick to give it up. The solution CAN NOT be very difficult or complicated, but sometimes it is in tiny details. It can be only in 3 things: Fuel composition, heat or vibration.
Although it is generally not recommended to pull the solenoid from its housing, I think it is wise to check if there is not dirt or a scratch-damage in the housing or something like that.

To remove solenoid, best is to twist it when pulling out, to break friction of the O-ring.

mk13

I tried with the "evaporated" gasoline, no change.

I did an other test without the valve in the fuel line, the engine run not bad, and stayed running a long time without cutoff :


I will do an other test with the valve connected to the fuel line but not electrically connected.
The aim is to identify if the problem is due to valve running or only by the housing cavity

1967brutus

That is dissapointing...

Please do this test with the LA, and then such, that the solenoid is BETWEEN the main needle and the carb.
For the purpose of this test it is acceptable to use longer tubing in order to get some distance between the solenoid and the engine.
The reason for doing it like this, is that with the solenoid unpowered, there is no pressure drop over the solenoid, instead the pressure drop is after the main needle.
IF the solenoid is leaking, but in the line before the main needle, there is no low-pressure, therefore also no bubbles.
With the solenoid, just for this test only, between needle and carb, the assembly will be subject to low pressure and any leakage will show.

IF leaking, there is the option of the solenoid being defective, or the housing can leak. The side tube (inlet) is glued in the housing, and there is despite my best efforts a possibility that this joint is leaking.
You can try sealing that joint by covering it all around with some Epoxy glue.

If the solenoid is defective, no other option for me than to send you a new one, but since I do this for zero profit, I would really like to be sure.
If you find the leak in the housing, I suggest you send that back to me, and I will exchange it without cost, but I like to have the housing in return so I can investigate and repair it.

I want to do my utmost to get you a working solution (and I am 100% convinced it WILL work, since I allready run gasoline now for 7 years and have never seen this issue) but as said, I do this for zero profit, I also would like to minimize my financial losses (no profit margin from which I can "buffer" these costs...).

1967brutus

One kind request: Can you please use your phone in "landscape" format? Holding your phone upright will cause a smaller screen when the video is played in full screen mode, and this leads to loss of detail for me.

mk13

I watched lot of your YouTube video this afternoon, and when I saw your first tests without the solenoid it gave me the idea to do the same thing and see what happens 😁😁

So, I come back from my bearing shop and they can order for next Monday a new o-ring for the valve.
I bought 3L of fresh 95E10 (for a test tomorrow).

I will do the modification on the 25LA than you advice me (solenoid off, between the needle and the carb).

If I find in my mess some pneumatic fittings, I will try to put under a small pressure the housing + solenoid, and hunt some leak in a cup of alcohol.

Don't be worried Bert, I will do all the possible test to check the integrity of the solenoid, and if there is an issue we will find a solution together, I know you spent already a lot of time for this gazer conversion and you don't benefits, and I really thank you for that! 👍

I will try to thinking to hold my phone in landscape for the next video, sorry I'm a YouTube noob 🤣🤣

Regarding the vibrations, I tried holding the solenoid by hand while it was running but it didn't change much, still bubbles.
​​​​​I also thought about putting a piece of rubber between the engine and the chassis, but I'm not sure that a few millimeters of rubber significantly reduce the vibrations... What do you think?

1967brutus

The persistence of the "big" bubbles, I had a hard time accepting but it leaves little other options than there indeed being a leak of sorts, and that would be for me at least, the first time to see that in the solenoid/housing combo.
If that is truly the case, I will have to review the way I fit the side-tubes. No way around that.
Vibrations make microbubbles, not big bubbles. Microbubbles CAN collate into larger bubbles, but NOT in this rate... That would typically be one 2 mm bubble every 10 minutes or so, IF there is a loop in the ful tubing where the bubbles can collect. The way you show it, with the fuel outlet of the solenoid pointing upwards, and STILL big bubbles, can't be anything else than a leak.

We have to figure out which part is leaking so I can replace the proper part.

One thing is sure, your engines CAN run on this system, I myself run engines with much smaller fuel consumption so that really is not the issue.

Meanwhile, what is your impression WRT lubrication? I have so far very limited experience with bushed engines (only an OS FP10) but I like to collect as much data as possible, because there are a lot of those bushed sports engines out there.
Do you notice a difference in the quantity of oil coming from the shaft?

EDIT: as an afterthought: you mentioned pneumatic testing. My request is to test under negative pressure, not positive. Sometimes, leaks along seals can have the character of a non-return valve. It is not unthinkable, that the leak opens up under negative pressure, but seals itself under positive pressure.

Jim.Thompson

Does this one look like a suitable example?

https://fr.aliexpress.com/i/10050060...yAdapt=glo2fra

I notice that these have been developed for 30 cc two stroke engines.
I have two converted 2 stroke industrial engines in commission in planes.
One is a 40 cc Kioritz.
The other is a 26 cc unbranded Chinese engine. (This one runs a 17 x 6 prop at just under 9000 RPM with a WT 668 Walbro clone carb at the present).

I am keen to experiment with the M Tronic cloned carb on one of them.
(I have a long period of no flying ahead of me now - plenty of time to experiement).
Which one would be the best to start with in terms of compatibility?

Jim.

Jim.Thompson

I would be interested in further details of this carb conversion, (if it is possible to describe in print and pics etc.).
If necessary, in a separate thread to avoid potentially distracting the focus of this one.

However, I will most likely go the easier way and find a clone M Tronic carb and give this a go on either my 26 cc or the 40 cc two stroke engine I have in planes.

Thanks for posting.

Jim.

1967brutus

Someone from France that I communicate with outside this forum said that these carbs look like the real deal...
Given the price that almost seems like too good to be true, but, hey, for that money, to me it seems worth a try.

Jim.Thompson

Thanks for the reply Bert.
I will probably order one and try it on my 26 cc two stoke first.
What thread will I go to read the details such as:

1. What drives the solenoid? PPM directly from a receiver? Or what?
2. Do I need a separate amplifier or electronic "driver"?
3. Are these details explained in this thread?

I don't expect you to write detailed responses out again, as I am sure it all has been explained in several long threads.

Jim.

1967brutus

If you are able to build, or have access to someone that can build electronics for you, you can build Dave's controller, otherwise I can send you one (would have to check the shipping cost, but probably around 30 Euro total incl shipping).

That small piece of electronics needs to be hooked up to the solenoid.
You will need a TX with decent programmability, like OpenTX or comparable.
A separate channel slaved to the throttle, programmed with a multipoint curve, controlling the solenoid, allows you to tune the engine over the entire throttle range.

That is it in a nutshell.

Jim.Thompson

I am able to build electronic devices.
Where do I find details and circuit diagrams of Dave's controller?
Here in this thread?