mk13

Yes you have right, with oil in gasoline the bubbles are significantly smaller (but there is lot of small bubbles).

I use a synthetic oil for 2 stroke from my supermarket (I can't remember the brand).

Yes I have for the moment the open curve from Guillaume. I will try with the solenoid electrically disconnected to set the needle a full throttle and after set the solenoid curve.

I will check the exhaust pressure line tomorrow if I find some leak, and will do the test of disconnect exhaust line from the muffler at full throttle.

​​​​​​Thanks a lot for all your way of investigation!
I hope I will find the root cause in the next days 🤞

1967brutus

Good luck testing, I am pretty sure we;ll find a solution, and this is exactly the reason why we should do this in the open discussion, not via non-public private messaging.

Let the learning continue!

1967brutus

Something completely unrelated to your problem, just sprung to mind: You are basically, of all people involved, running the smallest engine yet in this entire saga.
I have converted an OS FP10, and when doing so, I pulled the head and noticed that these small OS engines have a rather thin cylinder head. For the FP 10 this resulted in a sparkplug that protruded way too deep into the combustion chamber.
Please check if this is the case with your .25 engines, and if so, add an extra washer under the plug. The threaded base of the plug should be, as a minimum, flush with the ceiling of the combustion chamber, or even slightly recessed, since the electrodes will be pretty close to the piston top otherwise.

It has nothing to do with the bubbles, but a protruding spark plug will negatively affect the scavenging process of these tiny 2-strokes.

Jim.Thompson

That makes sense, I should have guessed. Thanks.

mk13

I checked the position of the spark plug in the combustion chamber and it's ok the thread of the sparkplug is flush.

You say you have converted OS FP10, so this engine is smaller than my 25RC or my 25LA ? I don't understand something?

I tried today to set the needle with the valve off at full throttle, and after set the valve on each point of the curve, it's a little better but still bubbles.
So, remove the valve and try to run the engine directly from the tank, and it's not too bad.
So, this afternoon I went to my club to do a flight test, the plane fly not bad en the engine run good, but each time I have engine cut after some minutes and I must do emergency landing (without crash 😅&#129310
I saw some bubbles (always that!) come from the needle. I don't know if I have a leak on the needle seal (I already have a piece of hose on the needle to improve the airtightness) or it's due to emulsion.

The research continu 😅

Bert, what coil do you use on your strobe light to check the timing ignition? (Wire diameter? How many loop?

​​​​

mk13

An other question, how you receive the tachometer signal from rcexl ignition on your Taranis? Do you use a interface module?
Thanks in advance! ☺️

1967brutus

Hmmm if you had bubbles even with the solenoid completely out of the loop... THAT is weird. The only reason I can think of, is some form of heat transfer.

I don't know the exact coil size. I do know it is not very critical, I tested three different Henry-values and they all three worked equally well.
It's a tiny thing (I believe they call it a "choke coil") maybe 1 cm long and 5 mm diameter or less.

Yes, indeed, I did run an OS FP10 on gasoline (1,7 cc, so yes, pretty much smaller than yours), but I never ran it with the solenoid because despite having all the electronics and stuff, that project got halted. I still want to finish it.

1967brutus

https://www.rcgroups.com/forums/showpost.php?p=39141981&postcount=18
Read post #18
The coil in post #1 of that thread is what I also used for the stroboscope.