Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

OS 50 sx with Macs tune pipe

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Old 10-03-2013, 07:05 AM
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izzy-israel-73
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Default OS 50 sx with Macs tune pipe

G'day have a few problems with tuning in my 50sx not getting any real response an the mixture screw !
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Old 10-04-2013, 12:23 PM
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Not a 100% sure.. But do have a leak anywhere?? Case or carb??
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Old 10-06-2013, 06:55 PM
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Test the muffler/ tuned pipe pressure fitting for restriction. A fuel line restriction like a kink, dirt, too small a line, bad in-line filter or filter-clunk. A fuel tank that's too low can cause problems. loose the fuel-er valve if you have one.
PS, If you can't keep bearings in that 50 SX, scrap it, the case bearing bores had bad alignment in many of those.

Last edited by freakingfast; 10-06-2013 at 07:00 PM.
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Old 10-10-2013, 07:40 AM
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Pipes do that. Just run as rich as you can on the high end needle. An in flight adjustment helps for the high end too.
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Old 10-10-2013, 02:55 PM
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I really like the technique of underpropping a piped engine for ground/bench runs so the static rpm is in flight rpm range, allows the pipe to be tuned quite accurately if that is needed, and also assists in setting the needle if the mixture seems elusive. 10% trimmed off the tips for sport engines, 15% for DF type engines on props seems to work - I didn't come up with those numbers. Fuel demand goes up with rpm, but suction at the carb does not follow in linear proportion so the mixture goes lean if the needle is set for ground rpm.

BTW - izzy - is this a MAC's "pretuned" system? Or a la carte with a stock header and pipe?
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Old 10-11-2013, 09:04 AM
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no I brought the Macs header and pipe not baffled no its not a pre tuned pipe has to be tuned !
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Old 10-11-2013, 09:05 AM
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no all new lines !
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Old 10-11-2013, 09:11 AM
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that's what I have been doing lol, from the header to the tune pipe there's a 30 mm gap if I bring it in it goes lean but the problem is still there no really response on the high end side minimal , screw it anti clockwise to richen and no response !
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Old 10-15-2013, 08:12 AM
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It is likely going lean when the pipe is shorter, because it is on the pipe then and needs more fuel to make it happy. So yes richer, and richer again. Like MJD says, use a smaller prop for ground runs. In a dive, on the bigger props it will come on the pipe with little adjustments of the pipe/prop dia.
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Old 10-15-2013, 08:49 AM
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A properly set up fuel system is a closed loop of pressure that is capable of feeding the most thirsty 2 strokes in the world.
It there is any restriction [like dirt or crud in the needle valve] the system fails here.
If the tuned pipe coupler leaks..same idea, loss of consistent pressure.
The nipple at the pipe CAN rarely become clogged
The crankcase seal of the engine must be within serviceable limits.
Pin holes in the fuel line pick up tube, or being connected to the wrong line........it is handy to have a big 2 oz syringe to troubleshoot pressure leaks and to actually suck out clogs sometimes.

Yes, if you are running too much prop and the engine is too hot as a result the engine will not respond to mixture changes if the piston is over expanded, shut it down.
Make sure to use at least 20% oil if you know exactly what you are doing and 25% oil if you do not know what you are doing.
[I use 25% oil quite often]

Last edited by combatpigg; 10-15-2013 at 08:57 AM.
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