Another version of how not to build a model engine

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NickG:
S, now it is controlled by cam you can put a stronger spring to avoid any bouncing. I don't think it would though, as soon as it gets to its compression stroke it would shut and stay shut until there is an underpressure in cylinder.

Nick

sorveltaja:
Repaired camshaft:

Stronger spring and tappet added to inlet valve. Engine is now ready for testing:

sorveltaja:
Testings with new inlet cam didn't make the engine run. At first, the cam was rather egg-shaped, having too long opening/closing time, so I filed the cam a bit, to make the valve opening and closing more rapid:

After that, engine fires, and also runs at fast speed again, although I have tested it only with 1.9mm carb this far.

Addition: I tested the engine with 0.8mm carb also, and got similar results, as with spring-loaded intake cam. Engine fires, and almost runs.

sorveltaja:
Current status of the engine. Hopefully it's noticeable on the video, how the engine responds to carb needle:

Previous sparking plug started to push out its ptfe insulation, causing severe running problems, so I had to make new, bit modded version, that should keep the insulator in place much better.

Test setup on the video:
Fuel: regular 95 gasoline with small amount of motor oil
Carburetor is the older one 1.9mm throat with 1.5mm hole ptfe plug in its butt its throat.
Ignition timing was about tdc(top dead center). I have tested both advancing, and retarding the timing though.

Generally, the engine has began to show more responsibility to the carb, and also it starts easier.

Maybe it just needs plenty of short running-in sessions.

bogstandard:
S,

It has only just clicked with me :doh:, you are not using a throttle on the carb, so all you will ever get is high speed running, which is correct. When you adjust the needle, all you are doing is making the mixture more or less efficient, either weak, correct or rich. Just like a normal model free flight or control line engine.

What you really need is a throttling carburettor to give you speed control, which is a little more difficult than what you have now, but achievable.

John

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