Clarification: Drilling out the air intake without damaging the seal.

The back plate is made from zinc. It's soft. the tank is aluminum, soft, but not quite as bad. The trick is to drill accurately to retain the original factory "O" ring seal between the tank and the backplate. We used to use an old c'case, bolted the backplate/tank assembly to this c'case for accuracy, jigged up the old c'case in a drill press, then drilled out the air-intake. You'll not have an alignment problem if you do this, nor will you damage the seal.

One other item: We had an engineer upstairs. His name was Dave (not me). I have since forgotten his last name. His goal was to make a reeded engine with c'case pressure to the external fuel tank. He drilled out the air intake to 0.080". Used a 0.012" mylar reed, carefully drilled and tapped the side of the c'case right on the circular run where the connecting rod bottom end runs, and carefully dremeled it off to prevent interference. The hole was tapped, but there is not a lot of material there. The small fuel nipple was then Loctite RED into place.

He only got it to run one time that I recall. But oh man, did it scream! I recall about 21k Rpm on a 6x3 glass....but was unreliable. Your tank must be small, and all the piping absolutely air-tight. The reeded .049/51 just didn't have the c'case pressure/volume to make it work. If you had a full tank, and allowed the engine to start with a full tank it would work. But if you tried to start it with less than a full tank, the little engine just didn't have the c'case pressure volume to catch up. TeeDee's were the exception. Key here is to use a small, I mean small fuel nipple and small line.

I would NOT suggest this as a mod. Too tweaky and too unpredicatble. With the "carb" opening this wide, maintaining a fuel flow without pressure is not possible. I've only seen it work with a 1 Oz tank, and then full to the gills before initial start. I don't remember if this was retested with a smaller than 0.080" carb opening or not. I would bet not. Too much unorthodoxy and too unreliable.

Now, engines are rare. Then we could go grab a handful of the engines and butcher away with impunity.

One other item of note: This pressure mod was only attempted on the plastic backed engines installed in product, like the plastic P-40's and such. That much drilling on an aluminum tanked engine would destroy the "O" ring seal.


FYI


Dave............