Have a Saito 100 inverted in my plane and a 3 line fueling system from tank to engine. When filling tank the fuel seems to be coming out through the carb. Would going to a 2 line system and use a filling valve solve the problem. Can't fuel directly from carb line because of cowl. Any suggestions would be appreciated.

Sounds like the tank is mounted too high above the carb.  The only way I know to deal with this is to use a hemostat to pince the carb fuel line while you fill the tank.  Don't release the hemostat until you're ready to start the engine.  Don't open the carb past idle until the engine is running.  Only other option is to fuel the plane inverted and turn the plane over when you're ready to start.  Both options are a pain, but about all you can do without lowering the tank.  A two line system will not solve the problem.

pmw

Even lowering the tank may not solve the problem. Even of the tank is level with the carb, once the tank is more than half full the siphoning will start anyway.

Would going to a 2 line system and use a filling valve solve the problem?


Yes it would.

The fueling valve would solve the fueling problem, but the fuel would still siphon into the carb when the valve was closed for start.  If you don't delay the start after fueling or open the carb too much, you should be okay.

Check any restriction in the vent line that may create pressure inside the tank while fueling.
Try keeping the throttle trim all the way down (minimum) after fueling and before starting, so the low neddle helps blocking the fuel.

Copied from http://saito-engines.info/faq.html:

Q. I want to install my engine inverted. The guys in my club say you need to install an on-board glow driver for inverted 4-stroke engines. Is this correct?

A. There is no need to use an on-board glow driver if the idle mixture is set correctly, you are using an appropriate brand glow-plug, and proper fuel. The idle speed will be reliable and just as low as for an upright engine.
Make sure the tank centerline is about level with the carb or a little lower; inverted engine problems are often related to the tank position being too high.

I'll second that-the guys at your club are wrong. Proper tuning and good fuel and the engine won't care which way you mount it. Some of the cheaper 4 strokes won't let you fine tune in some cases which can be a pain but for most people they simply have the low end to rich and poor fuel which it won't Idle well upright.

Everything that French said. The topic about glow drivers is alive here on RCU right now. Idon't use them but if it makes the pilot happy then Ihave no problems with them, it's a piece of mind thing. When I install the engine inverted Ido make up my own remote glow driver, Idon't care for the store bought systems at all. Once you have the low end adjusted correctly there really aren't any problems. Ido run OS and YS engines though so that could be one of the reasons Ihave gotten away without adding the drivers?

The main reason siphoning happens is due to tank being too high. Tanks can be much lower than is generally thought and work great. yes a 2 line filling valve will help. Some have had problems with them. I have also but generally after they get old and O ring gets stiff. Get tank lowered that alone may do it for you. how much lower? I suggest a 1/2 inch below usual. It probably won't siphon when filling since nose of plane is high at that time. That's the main problem with inverted engines, carb center is much lower than tank.