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bgx1 and tuned pipe

Old 05-06-2005, 09:09 PM
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Default bgx1 and tuned pipe

[8D] Hello all, I have a BGX1 with an os header and os tuned pipe that sneezes out the carb on acceleration. Have the extra head shim installed according to OS instructions. Has a 18-6 classic style wood prop and tached it at 8500. This thing is a beast in my scratch built 81" Sukhoi that weights 13.75 lbs. Running 10% Powermaster fuel. Flew it today for the first time and this plane is way overpowered but just what I was looking for in a plane\engine combo. Anyhow I tried riching up the low end little by little and it seemed to help but then became burbbly rich in the middle and still was sneezing 1 out of 3 acceleration tries. Finally settled on the rich side of the high needle and somewhat rich on the idle needle and flew it. Wow what a power monster and was quite the plane to land, talk about coming in hot! Took three tries to get slow enough to land and not over shoot, BUT on throttle up for go around engine would sneeze once or twice then spool up and seem fine. Has anyone had this problem before (sneezing) and could you give me some advise. I believe it is too lean on the transition from low needle to high needle.

Thanks Bryce
Old 05-09-2005, 10:47 AM
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Default RE: bgx1 and tuned pipe

First off, make sure you have excellent fuel delivery. The O.S. Max BGX-1 needs good fuel delivery, especially if you're using a pipe. We replumb the entire fuel system with large tubing. This may require a different fuel tank because some tanks won't let you replace the tubing inside with larger. On a Sullivan tank, we go with tubing that has an I.D. that's the same as the O.D. as the stock tubing. We go with Large fuel line. This requires that we wire-tie everything in place...the large tubing won't stay attached on its own.

Make sure the tuned pipe is actually tuned. You can't just bolt it on and expect it to be right. If it's a bit long, the engine will trend rich, and if it's a bit short, the engine will trend lean.

Tune the pipe by starting out with it long. Start the engine, lean to peak RPM and tach it. Now shorten the system by 1/4". Start, leant to peak, and tach. As long as the RPM climbs, shorten the pipe. You must stop the engine each time and reset the needle. Adjusting the system like a trombone won't get you a good set.

When the RPM doesn't climb after shortening, leave it there. Fly the engine. Listen carefully. It will have a distinct sound when it's on the pipe. You may need to adjust the pipe length depending upon your flight tests.

Adjust the idle mixture as necessary once you have the full-throttle needle and pipe settings found.

You also may be trying to idle the engine too slowly. Anything under 2200-2400 RPM is considered good. If the model flies too fast at that RPM level, you'll have to try a different propeller.
Old 05-09-2005, 12:10 PM
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Default RE: bgx1 and tuned pipe

Thank you very much Bax. I will do length tweaks and experiment with the header pipe length. I can hear it come on the pipe but it is subtle right now and it is the baffled tune pipe. Sneezes coming up to half throttle at a moderate rate but sneezes in the air at a steady half throttle periodically. Yes it does come in very hot with that prop. Once the wind dies down around here and time permits, then its time to play!
Thanks again, Bryce

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