Back and forth

Beazld Sun May 05, 2013 5:38 pm

What does it indicate with a reed valve engine when the prop oscillates back and forth instead of rotating? Huh...

microflitedude Sun May 05, 2013 5:54 pm

1 - The engine is flooded and can't get going with too much fuel in the cylinder. Blow the cylinder out via the ports and try again

2 - The compression is too high, and the engine can't turn itself over all the way because the pressure on the piston is too great. Add a head gasket or two to lower the compression.

3 - The prop wasn't flipped hard enough to complete a cycle, bouncing the engine between cycles. Flip harder.

**RknRusty** Sun May 05, 2013 6:10 pm

Nothing I can think of to add to that. Most model engines will do it when flooded. My Thunder Tiger does it and spits at me like a Cobra. When I was getting the hang of cranking that one, I needed a shower when I was through. It actually backfired through the venturi once.

Ken Cook Sun May 05, 2013 6:26 pm

It's an indication that the engine is over compressed and needs more head gaskets. You could also lower the nitro a tad but if it's at the required content then reset your deck height by adding more shims. Not all gaskets are the same in thickness and having a instrument to measure them is important. Going to far will inherently reduce your power and starting ability, but, I would start with one at a time and the engine should be happy. Ken

Beazld Sun May 05, 2013 6:51 pm

Thanks guys, probably over compressed. Running 25%, 2 shims and Merlin head. I'll add more shims and try again.

**RknRusty** Sun May 05, 2013 7:11 pm

Beazld wrote:Thanks guys, probably over compressed. Running 25%, 2 shims and Merlin head. I'll add more shims and try again.

If that's the Merlin head clamp with the Glo Bee drop-in, it's definitely over compressed. Those suckers are way higher compression than a Tee Dee stocker. I usually find mine do best between 3 and 4 shims with 25% nitro. I have run as many as 5, but usually not. Those heads do run well after you get the compression right.

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