I recently completed a Brodak Oriental with an inverted engine.  This is not an ARF.  When I go inverted or do any outside squares or square eights the RPM drops off to the point that I have a hard time completing the manuver.  I know the typical fix is to raise the tank.  I can't do that because it is resting on the motor mounts.  It has been suggested that I lower the engine by using aluminum shims.  It looks like I don't need to move the engine very much, probably less than 1/8 inch.  Would this create a change in the thrust line enough to create control problems.

The following are the spec for the plane:

LA 46
BYO 11-4 prop
Sig 10% Castor Fuel

  Moving the engine is not going to screw up the performance. I would however suggest that you move the uniflow vent on the inside of the tank instead. Just move it in the direction you need the tank to go about 1/8". That will effectively change the fuel delivery pressure without requiring any other fiddling.

    Brett

Brett the tank I am using is a 4 .5 ounce Uniflow wedge tank I presume you suggest that I un solder the beautiful tube and move it so the internal end of the tube is raised approximately 1/8 inch is that correct thanks Pete

Yes.  That's what Brett is saying.  It's what I said, too, but either I forgot to push the "post" button or something happened to my post.

Remember that the tank will still be beautiful when you're done, it just may be in a goobered-up sort of way.

If you use a clunk tank with a fixed uniflow then raising or lowering the uniflow would do the same thing as adjusting the tank height (you see people talking about that here).

I don't know what you'd do with a clunk on the uniflow -- you'd probably have to adjust the tank height, because the clunk would always be seeking whichever side of the tank is currently "bottom".

Peter   Yes using a plastic clunk will work if you make the uniflow a fixed tube. Do not attach it to the pickup. The problem is finding a clunk tank that will fit. Reworking a metal tank is easy. Just buy a 125 watt gun and move the tube. I use a propane torch to heat the back of the tank and flip it off with a screw driver. Unsolder the uniflow and move it. Use the iron to resolder the back onto the tank.
 I would use the aluminum shims under the motor. You should ALWAYS use aluminum shims to keep the mounts from crushing.  y1Building 101 use shims
Ed

I wouldn't use a torch to remove the back unless you have flushed out the tank with water. I have seen them explode. While not a huge explosion, it can be enough to cause injury.

"You said I have seen them" It must be that you your self have had them do it. I have never seen one explode. A small "puff" yes .Then I was the kid who always lit a match to the end of a empty fuel can just to see how far it would go across the parking lot. WE would add more fuel and shake the can and do it again. Every time I open a fuel tank I think of those good old days. Here is how I have done it, Tank is in vice,torch heats bottom of tank and I use a screw driver to pop off end. I am never in line with the back of the tank and I am two feet from it. I have heard that people heat the tank on the stove. Now that sounds bad. Also fuel will still burn sitting on top of water. I am all for safety so if you feel it is necessary to flush the tank with water,good. There is nothing wrong with being carefull
Ed