Bad Uniflow was "Pump"

[John Pavlick]

Sorry if this goes through twice. I sent it but I never saw it hit the list:

Jay,
 RE- Uniflow: That is a "bad" Uniflow setup (the one OS shows). Instead -
build one with 2 flexible lines and clunks: one goes to the carb. the other
goes to the muffler for pressure. Keep the rigid line that goes to the top
of the tank as the overflow line. This should be plugged when the engine is
running. Only un-plug it when you re-fuel so that you know when the tank is
full. Fill the tank through either of the 2 lines attached to the clunks.
This will work. Trust me. I have this setup running on a 3D airplane with an
OS 46LA. Like the LA, the FL-70 has an air-bleed carb. so this is one way to
get it to run (especially idle) somewhat reliably if the tank is higher than
the carb. You can't just place a check valve in the pressure line to stop
the siphon because the motor won't idle reliably (WAY too rich at idle).
Building a Uniflow the way OS suggests will allow fuel to siphon into the
muffler (as you noticed). Building it the way I suggested will not totally
eliminate this problem but it will GREATLY reduce it. What have you got to
lose? Give it a try.
 Re- The pump: I don't know if you should run an air-bleed carb. with a pump
or with any significant amount of tank pressure (i.e check valve in the
pressure line) for that matter. This suggests that mounting the tank on the
C.G. is not possible. Air-bleed carb's are not the best thing in the world.
They're cheap, that's about it. If you look at all the stuff from Perry,
they don't suggest using a pump with an air-bleed carb. I don't think it's a
good idea either. What made you choose this motor over the FS-70 Ultimate?
That would have been my choice. What a great running motor that is (no
matter how it's mounted or where the tank is)!

John Pavlick
http://www.idseng.com


John Pavlick
http://www.idseng.com

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