Every pattern ship and control line stunt ship that I have seen for the last couple of decades utilizes inverted engines. Not all of them were powered by a YS four-stroke engine. Many have been powered by two-stroke sixties and four-strokes of other brands. All performed flawlessly when the operator knew what he/she was doing.

All of my models, whether sport, fun fly or pattern are expected to have the engine running at the end of the flight. I perform inverted spins, slow inverted flight, inverted flat spins, etc. I have yet to meet an engine that cannot be made to run well and reliably inverted.

So what is the secret? Set up, fine needle tweaking and proper break-in. Not necessarily in that order.

Break the engine in properly on the bench. If the engine is showing any sign of a problem with reliability after you have tried all of the variations available to you, send it back for servicing under warranty with a note describing exactly what you have tried. Sometimes engines leave the factory with unknown defects. There is absolutely no reason why you should have to put up with a defective product.

Once your engine is broken-in properly, ensure that the centerline of the model's fuel tank is slightly lower than the spraybar of your carburetor. Usually, no more than 0 to 3/8ths of an inch is the proper amount. In short, nothing else will do. Any higher or lower will affect the running of your engine, unless it is a YS, pumped other brand or an engine using a Perry VP-30 pump or other third party regulator. An engine is not defective if it is suction feed only and the fuel tank is not at the proper height.

Use glow plugs that are recommended by the manufacturer. Believe it or not, they generally know what they are doing.

Use the recommended fuel for the engine you bought. Too much nitro in some engines can cause as many problems as not enough nitro in the fuel for other engines.

Use a prop within the recommended range suggested by the manufacturer. Overheating will ruin an engine much faster than over revving. Keep that in mind.

Make sure that plenty of cooling air can reach the engine. Equally important is the exit size for the cooling air. Since the cooling air is now hotter, after cooling the engine, it will expand and it will need a much larger exit opening than cooler incoming air.

No one is born knowing how to do this stuff. Those that do know spent the time to learn. Many also look back and realize that the learning process was the most fun. Don't feel bad if you don't know how to make it run right. Get determined and figure it out. You can do it. I did.

Good flying.