(Asking this for my friend . . . I’m all e-power now.)
His full-fuse, inverted engine model has the typical spraybar location with the fuel line connection nipple on the outboard side of the model. This puts the needle valve uncomfortably close to the muffler. Changing to a different style muffler is not an option. He’d like to turn the spraybar around so the needle valve is now on the outboard side away from the muffler, and the fuel line connection on the inboard side. Is there any downside to doing this? Any effect on the way the engine will run?
I have seen it done and it worked OK, but not the optimum set up. The fuel line length increases, and it has to go against centrifugal force as it passes behind the engine and then has to go forward to the inlet. It can almost double the fuel line length. I would work out something for setting the needle valve with out burning your fingers. I would not make it longer, as the vibration for the engine will make the end dance all over the place. If it's a ST needle, you can make an adjust like some speed guys use made from a length of brass tube, and has a slot on one side of the end running lengthwise for 1/4" or so. the slot picks up the bent leg of the needle and lets you turn it. Put some sort of handle on the other end. this takes some practice and thought on how you do it so you don't stick the adjuster in the spinning prop!! Another option is a rear mounted needle valve. If this is an OS engine, they made a plugged spray bar for this. If you can find the parts from an older FP R/C carb, or even a FP rea needle valve set up, that puts your fingers in a better place. The draw back here is that the newer style needles like that come with the LA series engines have really crappy O-rings and they can leak air. Applying some heavy grease in that area helps with that, but the problem is eliminated with the older, all metal NVAs. Slow combat guys like using these as they give a better setting. The other draw back is learning how much to choke the engine for starting and setting up the tank for a quick, clean shut off when empty. If it's not right it just keeps surging near the end and if flying a contest flight could put you over the time limit. Having the back end of the tank shimmed out helps here also. I set up several airplanes for the all metal rear needle valve when my son Sean was younger and still needle shy. It makes no difference how the engine runs if everything else if right. It's tricky because your mixture is being set at the back of the engine instead of right there at the venturi/crankshaft pot. So he has some options, he just needs to think about how he wants to go about it and what might work best for him.
Type at you later,
Dan McEntee