I have 2 os 30 4 strokes and both have the same problems they are I can take off and fly around for about 10 minutes then land refuel and fly again all of a sudden the motor will either quit on takeoff or fly for 2or 3 minutes and then quit I have been using the same fuel in all my 4 strokes for years with no problems , I have changed the position of my tanks changed fuel lines and god knows what but to no avail my fuel mixture is 15% castor oil 10% nitro and the rest methanol can anyone help thanks in advance

We can only suggest that you put the engines on a good test fixture with a good tank and good fuel-line plumbing. Use good-quality fuel and a new Type F glow plug. Run them and see how they go. If they run well, then the problem is not the engines, but in the airframe/engine/mount/fuel system combination. Vibration is easily a culprit that can be difficult to track down.

Thanks Bax I will try all that this weekend and let you know how I go

tried all the things you said it seems to be ok the only thing that I found is the motor gets hot ,when I say hot very hot all indications say yes the motor will run ok which it dose but I have not tried it in flight btw I am only 100 ft abmsl regards John

If the engine runs well, but becomes hot enough to burn you, then you have a normal engine. If it's truly overheating, then it will allow you to accelerate it to full RPM, and then the RPM will begin to sag, as the engine overheats and starts to seize.

G'day Bax flew on the weekend using your recommendations both 30's performed well thanks for your advice