Leaning out OS 25 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 02-05-2008, 03:06 PM   #1
Thunder Chicken
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Leaning out OS 25

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I have a head scratcher here. Its an OS .25 max FP. It seems to have good compression, i cant really tell if the crank bushings are in bad shape or not...it feels no worse than my 40.
I did buy the engine used from e-bay, and when it arrived, the muffler was the wrong one for it, and there are cracks in the casting where the carb mounts to the engine. I have expertly goobed lots of gasket maker silicone stuff around this to seal it up, but maybe it is not sealed and is sucking air......
The thing starts up OK, idles like a dream. With the high speed needle set at about 2 turns, its rich at wide open, and after leaning it out about 1/2 to 3/4 of a turn it peaks out, then I'll richen it up a bit, point the nose up, and it is ok. After a bit of fuel is burned out of the tank, say 2 minutes of running, when i point the nose up, it dies off, but if i richen the high speed needle up, it takes off and runs fine again for another few minutes. This whole process repeats itself until i get mad at it and park it!!
I've checked my fuel lines for holes,including the clunk line, the tank is sealed up, and it is wrapped in bubble wrap to prevent foaming.
The engine is mounted on its side, so the muffler is pointed down and away from the plane! The carb is pretty much lined up with the center of the gas tank.
I've never mounted an engine sideways before, but have seen many like this, and cant imagine this being a problem, but maybe it is! It sure is frustrating!!

Thanks for any help!
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Old 02-05-2008, 03:30 PM   #2
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I had a Supertiger gs40 that was exhibiting the same problems. After replacing it with a new OS, I popped the head off a noticed a groove worn into the liner. The engine felt like it had loads of compression, but would never stay running for long no matter what the needles were set to.

Hope this helps.
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Old 02-05-2008, 11:21 PM   #3
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Hi TC,

What size of tank?

With my O.S.FPs/Mag.GP.25s on 6oz. tanks I find I have to start on the rich side to avoid going lean at the end of the tank.

Some other things to check:

-Is the muff. pressure nipple clogged/restricted?

-Backplate tight?

-the needle valve could be leaking air. Use a 1/4in. of fuel tube to seal it.

-looking down the carb throat, you should see about 1/16th in. of the end of the needle valve.

My (low time) FPs/GPs.25s run 14plusK on 15% with a MA 9-4
The (well worn out) ones can still get 12K

Don't forget they can't run as good as an O.S.FX.25 !

Good luck,

Take care,
Have fun,
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Old 02-07-2008, 06:15 AM   #4
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Keep the tank as close to the back of the engine as possible too. This really shows up when you put the nose up for fuel draw.
Tried for my kamikazi pilots licence. Flunked the test.
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Old 02-08-2008, 07:16 AM   #5
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I agree with Crosscheck. Make sure the pressure nipple in the muffler is not clogged. I had an OS 25 LA that would start and run and then quit. Turned out a small blob of blue locktight had stuck in the nipple. It took a while to figure it out.
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Old 02-09-2008, 09:34 AM   #6
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Thanks for the replies.
The pressure nipple was not clogged, however, the tank is back away from the engine a bit. I had to have the battery right against the firewall to balance it, but i'll move the tank right up front and try to run it. I also JB welded the cracks around the carb mount on the crankcase, maybe the silicone was not sealing it up.
The backplate was nice and tight, the gasket looks good.
I'll also try a new glow plug, just to see.
My fuel is wildcat 10% nitro, about 2 years old, but its been in my basement out of the sunlight. Maybe it is gone bad?? ( it seems to run fine in my os 40la)
Thanks for the advice!
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Old 02-09-2008, 12:50 PM   #7
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Originally Posted by Thunder Chicken
. Maybe it is gone bad?? ( it seems to run fine in my os 40la)
Thanks for the advice!

my os 40la will run on anything under any circumstances good little motor even if it's not a powerhouse
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