Hey Billy,
Im running a .001 headshim, irwins tuned pipe(collared down at the end with tubing for keeping in the heat), closed off cooling exit on the head and drilled a hole about 1/3 the sized of the original exit, lightened flywheel. I used a reamer that i had in my tool box(just happened to be the perfect size) to make the mod to the carb. Took all the guts out of it and started turning it untill the velocity stack was paper thin on the outer edge and a perfect taper all the way to where the barrel opens up. the final diameter where the barrrel meets the casing did not change only the way the air flows into the carb. Yes the mod to the sleeve is where it hangs down in the crankcase, under the actual inlet if you will. I ground a "channel" down in the metal about half the thickness of the sleeve, and the whole width of the port. Andy Brown was at our district 13 race last october and showed me one of his sleeves he does for all of the .21 mac engines. I did the mod to my .21 MAC and it screemed even more than it did already, so i figured Id try it out on the outboard and it did seem to help, just dont go to deep and break through the plating! I also put a little more taper on the bottom of the sleeve chamfer and smoothed it all out. Ive never had it radared but its alot faster than the only two other O.S. outboards in my club. I run Red Max 50% and it loves it. I either run a X437/3 or X440/3 prop. both with nuetral "tilt" on the engine. on a modified Herb stewart tunnel 29.5 inches in length. ~ Hope this helps, James
P.S. Come on! theres gotta be more O.S. modifieds somewhere out there, share some secrets!.
