stunthanger.com
Engine basics => Engine set up tips => Topic started by: Russell Shaffer on February 27, 2006, 06:11:09 PM
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I have a Black Widow that has never been able to make a consistant run. On the bench, you have to fiddle with the needle to keep it smooth, and in the air it is impossible. What am I missing here? Russell
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I am thinking you may have an air leak. If you ever took it apart, there is a chance you might miss (or have lost) the one tiny gasket between the plastic "venturi" and the tank back plate. If you lost it, you can make a replacement from a sliver of fuel tubing. Also make sure there is no leak between the reed assembly and the back of the crankcase. A leak here could cause a lot of problems.
Finally put a piece of fuel tubing on the needle so that it will seal the needle seat.
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Thanks for you ideas, Alan. That engine has never really run right. There were burrs on the back of the crankcase around the screw holes, when I looked for possible leaking areas they were quite apparent. I lapped the case back on a piece of fine sandpaper, changed the gasket (I actually had a brand new one!), and it ran out a tank better than ever. Amazing what a difference a smooth mating surface can make. I'll give it a flight trial if the wind ever stops blowing. Russell
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HI Russell,
Alan is quite right to suggest you look for air leaks.
The real test for fuel tank sealing is to plug both tank vents with your fingers while the engine is running. If the engine continues to run, that indicates a sizeable leak somewhere. With an airtight tank, a reed engine will perform aerobatics well as long as the fuel pick-up is fixed to the outboard side of the tank. Good luck.
Paul