I fly a rascal 40 with FX46 engine which is inverted in this plane. I constantly have the piston-jam (not sure what the exact term is) issue, some say its because of the inverted engine. I constantly remove the glowplug and move the prop to release the compression. Do you guys see this too? Is there a better remedy to prevent this (this annoys me a lot)!
tks
747

This should not happen that often if your tank is at the proper height. Also, remove the fuel line to the muffler when fueling so you do not put fuel into the exhast port when fueling. Some people start the planes upside down (on a cradle) and then pick the plane up and turn it over to taxi out and fly.

What's happening is that you're simply getting too much fuel in the cylinder when you are priming it. This can happen to an engine whether the engine is mount upright or inverted. I am currently doing a review on this same plane and the position of the tank in the plane was planned around the engine being mounted inverted, so that's not really an issue here. Just try to be a little bit more careful as you prime the engine getting ready to start it.

Hope this helps

Ken

Ah! Good old RC KEN!

Whats 'Priming' and what do you mean by ".....Just try to be a little bit more careful as you prime the engine getting ready to start it. ..."

What do I do when I start , I have an electric starter...
Thanks

Priming is turning the prop manually (WITHOUT a glow starter on) to feed fuel into the engine before starting it. Unhook the muffler fuel line, plug the carb with your finger, turn the prop two or three times. This feeds a small amount of fuel into the engine to start it easier.

The problem here is that when a 2-stroke engine is inverted, the head becomes a bucket and can load up with fuel that has no where to go, so, like a bucket, the fuel just sits there - it can't escape.

The easiest way to remedy this is to flip the plane inverted or sideways when fueling and starting.

The term you were looking for is "Hydraulic Lock" and as Ken said is caused by too much LIQUID fuel in the cylinder. Gas vapors will compress but liquids will not. If you force the issue it can bend/break parts inside the engine and out. Since you are dealing with an inverted engine and using a starter you may want to avoid priming. The start will take a bit longer but will still occur.

Post #2 had the most likely answer as to why you keep getting a hydraulic lock. If you use the muffler pressure line as the vent when filling you can overlook that the tank is full and it's trying to fill up the muffler. Getting an inverted engine to flood by priming with a finger over the carb is much harder to do because fuel then has to run uphill first before it can even get into the engine. After you figure out how to get fuel to run uphill then you have to be sure not to overprime.