franchi

Hello:

Today I took my ST G20/15D out to play and I could not find a setting that it liked.

On th ground it ran perfectly. Once airborne, it beagan to miss very badly and lacked power. The engine was set with what I and another Diesel "expert", deemed as a perfect setting. For the next flight , I increased the compression but the problem persisted. The next flight I increased the compression a tiny bit more and alas alack the engine was now over compressed! It laboured and had black exhaust residue on the plane.

The fuel was DDD.

Could this all be caused by a loose seal between the crankcase and the venturi ? The venturi actually rotated from vibration while the engine was running! The rubber "O" ring was too loose to form a seal. On the bench, the engine ran gereat but perhaps this was before the O ring failed..

On the ground, should the engine be given a bit more fuel and compression to compensate for the engine unloading in the air?

I was running an 8X4 prop today.

I have never had a problem settting a Diesel for a perfect run. It must be the leaking O ring!

Any help with my problem?

Tia,

Franchi

Warren B

Is the venturi a peripheral type with the spraybar through the rear or a conventional with the spraybar through the middle?
ST 20/15D came both ways.
If it is conventional then I doubt a leak would worry it very much, but a peripheral jet would result in a leak into yhe fuel gallery and I don't think this would be very helpful at all.

Another thing to check is the Venturi bore, the glow 20/15's use very large ones but the diesels use very small bore (about 1/8" for peripheral jet type).

franchi

Hello:

When I return from holiday, I will replace the rubber O ring on the venturi. This the only change that was made to the engine since it was run last.

The fuel should be good as I added a can of John Deere starting ether to it the last time that I used the engine.

Stay well my friends,

Franchi

Jim Thomerson

You might take a look and see how much the piston and cylinder are varnished up. I broke three ST G20-15s from varnish build up with DDD fuel. I had run many gallons before with no problem. This was some years ago.

controlliner

A bad day with a model diesel engine is better than a good day with a glow.

qazimoto

My Feedback: (1)

I presume that you're running DDD 1/2A diesel fuel.

Why add a can of John Deere ether?

It the fuel can is sealed, ie no ether smell evident then adding additional ether will seriously affect the fuel composition, and dilute the oil content..

Ether just doesn't spontaneously evaporate from a properly sealed container. .

greggles47

It would help to know the fuel mix you are actually running. DDD 1/2A fuel (or whatever) with additional ether added is going to reduce the oil content. Possibly to an extent that your engine has overheated & been ruined.

Recycled Flyer

So the ground setting was fine but in the air it began missing?

If its control line I am going to point to the tank and its fuel lines.

franchi

Hi All:

Just a few quick notes re the ST G20/.15 problems.

I added the extra ether to help replenish the amout of ether that had escaped from my storage tin over the year. I added about 6 oz. to the mix. I think that I have enough oil in the Davis regular Diesel fuel. Mr. Davis advised me to add 6 oz.of castor oil to the fuel if I were to use it for control line flying. This I did. I can only guess what lube he puts in his fuels. Since his fuel has a red tint to it, it may be a Klotz product. My fuel woks great in my O.S .40 that has a Davis head.

I replaced the "O" ring on the venturi so there is no leakage at that point.

I checked the tank and lines for problems but found none.

Just for laughs, I may mount a ST G20/.23 glow engine in place of the Diesel to see if it too has problems.

Thanks for all of the replies.

Stay well my friends,

Franchi