pauser98

I have a engine problem which has been bugging me for a few months. Hope someone can help.

The engine is an OS32Sx on a pattern plane, fitted with a tuned pipe. The engine starts normally,
tuned slightly rich, and throttle advance is smooth. However after taking off and flying for a minute or so,
it will suddenly cut off when the throttle is reduced. After landing deadstick, I checked the temperature
and I would say it's normal.

In spite of various combination of fuel mixture for high and low end, glow plugs, and even switching to
a second OS 32SX, the cut-off still happen! One thing is I noticed a lot of bubbles in the fuel line (at mid throttle)
between the high-end needle and the carb. One of two of the engine screws were also loose.

Could the bubbles cause this problem - cutting off when throttle is reduced?

Chris

w8ye

My Feedback: (16)

Yes, check your prop balance and maybe cushions your tank?

j.duncker

My Feedback: (2)

Have you checked tank and fuel lines for pinhole leaks. Do not forget the clunk line.

pauser98

Thanks for your responses. Today I change the complete fuel tank from another plane. Then I change all the fuel lines from the tank
to the engine. I padded up the tank with plenty of form. I use plumber tape to seal up the high end needle (just in case).

Now there is much less air bubble in the fuel line. This is good. Bit I noticed fuel droplets coming out from the tune pipe. The engine runs very hot and I have to stop it.

Could this be a blockage in the carb or tune pipe?

Chris

DarZeelon

Chris,


Using a tuned-pipe on an engine designed to run with a normal muffler (and I would say over 99% of OS.32SX engines do run with the stock muffler, or a non-tuned replacement), will increase the eventual compression ratio, often beyond what is good for the engine.

The result is most often burnt-out glow-plugs, or a need to use a richer mixture setting, to retard the eventual ignition.
But over-heating and dead-sticks can also be an onset of this.


Adding a head shim (to the existing one), or using 5-10% less nitro in the fuel (if you use 15% use 5-10% nitro), would often solve this.
The bubbles in the fuel-line would further compound this issue, leaning the mixture and advancing the eventual ignition.


Remember - the fuel controls in a glow engine control the ignition timing.

pauser98

Thanks for the reply. I am already on 10% fuel. At idle I can see the fuel droplets coming out of the tune pipe with the smoke. At full throttle, there is smoke so it cannot be lean, but on throttle back the engine cuts off. I think it could also be leaks in the fuel lines, or leaks at the carb gasket.

DarZeelon

Chris,


I suggest you go down to 5% nitro then.

There is nothing wrong with the fact that raw oil droplets are emitted from the exhaust of any glow engine, running on so much oil (15-22%)...

If you sniff those droplets, I don't think you will smell much methanol, or nitro; just oil and soot...


And since your engine has an ABN P+L set (no piston ring), you must use fuel that contains a good portion of castor oil in its lubricant package.

I hope you were not using CruelPower...