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Working for a 4-2-4 break

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Old 08-28-2011, 07:11 AM
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Default Working for a 4-2-4 break



I have never tried to set a CL motor for this type of run but I'm not able to get my OS 35fp to break into a 2 cycle run from 4 cycle. I have the motor running at about 9500 - 9700 rpm. My needle isjust a couple clicks on the rich side of changing to 2 cycle. Shouldn't it break into a 2 cycle run when I tip the nose up? My tank is a plastic 3 or 4 oz. dubro, my fuel is 10% nitro / 20% oil. I'd sure like to fly this bird before the snow flies. Any suggestions would be appreciated.

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Old 08-28-2011, 10:06 AM
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Jim Oliver
 
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Default RE: Working for a 4-2-4 break

The FP series wasn't designed for the 4-2 break, but there have been some (Len Neumann and others) that have had some success in modding the engines for this type run. Not worth the trouble and time, IMHO!

You didn't state your prop; you might load the engine with a bit more prop and get it to break, then the real problem with the FP series will become obvious; it won't want to go back to a four stroke. Some just use a fairly large dia. prop with flat pitch (3.5 or 4 inch) and run the FPs in a rich two stroke.

The OS LAS 46 is the only one of the common OS engines that is used with any success without lots of mods. On my LA 46 engines, I use 10/22 fuel (Morgan is now mixing a fine CL 10/22 blend), the original OS plug or a T bolt RC Long, a current production ST 51 NVA installed in the venturi, an APC 12.25x3.75 prop and launch at about 9000-91000 (depends on your location/altitude). Something less than 5 oz. for the pattern and I get a noticable break when pointing the nose up before launch and in most of the maneuvers.

Cheers,
Jim
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Old 08-28-2011, 10:38 AM
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Default RE: Working for a 4-2-4 break

Jim,
Thanks for your input. Sorry about the lack of info. in my first post. T'ws due to total ignorance of the problem. The motor has been timed and ported by Mr. Scott Reise in Portland. Myprop was a 10-6. I'll try an 11-4 on it and see if anything improves.
Thanks again.
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Old 08-28-2011, 02:38 PM
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Jim Oliver
 
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Default RE: Working for a 4-2-4 break

Scott knows what he's about; I would call him and ask for his input. He has made several mufflers for me, but no engine mods.
With the 10x6, depending somewhat on the model and line length, you will have to run pretty rich to avoid being too fast for "stunts".

I like lap time of 5.2/5.4 secs; gives an old man time to think a little.

Cheers,
Jim
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