OS 1.08 - Did I run it too lean?

by Mike Davis
(Ainsworth Ne 69210)

I have an OS 108 Glow engine that will only run for about five minutes. I have put new bearings in it.

It will run fine on the ground. The last time I tried to figure this out the engine idled for awile and we noticed it had fuel driping out the exhaust.

We turned the needle valve in 2 clicks and the plane ran the longest it ever has then died. Did we get it to lean and it died from getting hot?

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OS 1.08 - Did I run it too lean?

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Jul 07, 2010
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Try this ....
by: MIchael from Oz

G'day I have seen this sort of problem with big two strokes before because they need large tanks.

Try this -

Put about 1/4 of a tank of fuel in the tank. Now tune the engine for best top end then back it off (richer) slightly.

Now fill the tank. I will guess that the engine is now running very rich. It may be OK to fly but there is a good chance is it too rich to fly well.

The problem is the height of the tank when this happens.

One solution is to use a Cline regulator.

The other is to use a Uniflow tank arrangement. This has a second clunk in the tank connected to the vent line. The second clunk is set up like the main feed line but is slightly shorter so the two clunks do not touch. This is easy to try and it usually works. I am sure if you do a search you will find more about Uniflow tanks. Most control line tanks are of this type and they keep the fuel flow pretty fixed through out the flight.