I am interested in hooking up a pump to my OS .46FX for reliability, it's going to be mounted inverted. Do you tap the crankcase or the mufler for pressure with a pump ? Is there one that is more reliable than another ? I am new to pumps so any opinion would be appreciated. Thanks.

crankcase...nm

does the pump manufacturer show you where to tap it ? do you have to take the engine apart to do this ? to be sure you get all the shavings outa the case ? I would think that would have to be done that way to be sure there were no leftover abrasive particales left in the engine.

Typically, there is a small divot in a reinforced portion of the backplate. you drill that STRAIGHT in with a small bit. (1/32 is OK, 1/16 is too big) Enlarge the end of the hole to the outside of the engine case and tap for the brass nipple. (look for a small dia nipple... 8-23 is too big. Can't get one that's too small.) Be sure to clean up all metal filings. (the backplate should be OFF the engine while doing this!) deburr the inner end of the hole.

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its basicly a waste of effort on an O.S. .46 FX. The engine's already very reliable. Unless you plan on putting the tank more than 8 inches aft from the engine... don't do it. Properly tuning the engine will be all you need to do.

The O.S. FX series engines do very well when mounted inverted. The pump will NOT prevent you from mis-tuning the engine... It will make your adjustments easier to get WRONG! The pump pressure means the needle needs to be closed further, and a small adjustment will have more effect.

Mount the engine uproght on a test stand. Tune it properly. put it in the plane and LEAVE the needle alone! It'll work.

Hubber is correct, the pump will make it harder to tune. If you want better idle & mid range try an on board glow driver. But even that isn't required on that motor if it's tuned correctly.
later daveo

Simplest on-board glow is a battery and a resistor wired to the plug. You don't need full voltage of a single NiCd to give increased idle reliability.

Measure the resistance of your glow plug. You want a resistor with 1/2 to 3/4 of that value.

Put a Phono type jack between the resistor and the glow plug such that you can boost the glow power for starting by simply plugging in a 1.2 v source. Add a switch between that and the glow plug to turn off the on-board glow.. and allow charging with the boost jack. (don't have the boost jack cut the on-board battery out... vibration could then cause RF noise.)

I've never had great luck with pumps and I'm sure that's my own fault. Where I've had problems is the pump always provided too much fuel to the engine, causing it to easily flood. I too thought I would be adding reliability to the engine performance. In fact, all I added was problems. In the first place, My application did not "require" me to pump the engine. I now believe that you don't add a pump unless it's required as to supply fuel to the carb. As stated in other responses, pumping and engine that doesn't need it will cause adjustment problems. Well, maybe not quite stated in that way, pumping does add some differences in carb adjustment. Keep in mind, there is an adjustment screw on the pump itself. (Perry) Now you've added a third adjustment that has to be right for the engine to run correctly. It's easy to cause a flooding problem when using pumps, certainly in an inverted engine. The on board glo igniter sounds like a better way to go with your application. Pumps are great when needed, but if tank location is within required limits of the carb, I wouldn't use a pump. Happy flying!