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Engine basics => Engine set up tips => Topic started by: Dennis Toth on September 20, 2015, 09:27:26 AM
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I finally have a setup on my OS Max 25 (older baffle design) that makes it and me happy. For some time I have used the Max on my Ringmaster that has been flown in OTS and general fun fly service. This ship has had a Fox 35, OS 20FS, PAW 15 diesel, and the Max 25. The PAW and Max allow it to balance correctly without added tail weight and the ship flies reasonably well, got it share of hardware. However, with the diesel no one wanted to hold it and the car was not shall we say wife friendly.
The Max is an engine I rescued from eBay. At first I had a 0.267 venturi which I think is stock for the Max 30 (was laying in the engine draw). It ran strong but never constant. I tried for the 4-2-4, some days good most half way through it would break to a 2 and we were off to the races. I tried different fuels, nitro %, plugs, tanks (uniflow open, muffler pressure, conventional), props all with about the same result (although the conventional was pretty close but still was rich to lean not what I wanted). I then got a smaller 0.246 venturi from Jim Lee and this helped but didn't cure.
Finally, I though maybe it just wants to run. I had been running a 9x5 so I though I'll try a 10x4, it was close, ran constant through the flight but to slow. The baffled Max doesn't have the guts for the 4 pitch. I put a 9x4 1/2 APC prop and set it for a 2.5 - 2 - 2.5 and BOOM it was happy, had a 4.9 lap time (60' C-C) and I was happy.
Best, DennisT