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OS 120 Surpass FS Series

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Old 03-29-2011, 03:24 PM
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W.P. Hurst
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Default OS 120 Surpass FS Series

Should this engine have to be rich at idle, seems very rich, and a little lean at full throttle?? The only way I can get a good idle is rich, alot of smoke. That also gives good transition to full throttle. After throttling down from full, chopping the throttle, it will idle lean for a few seconds, then go rich again, rpms are a little higher then drop a few when it richens up. It does not stop running.I am using a APC 14x10, 15% nitro,and OS (F)glow plug. When I take the battery off the glow plug, the rpm's drop a little and it seems to richen some at idle. I can only turn the mixture screw very little, the "sweet spot" is very small. I checked the fuel lines to the clunk and everything is good. It runs pretty good in the air. It started this last summer and does not seem to be getting worse. Just don't want it to go bad when maybe a simple fix is in order. Some say it does not hurt to use 2 stroke fuel in a four stroke, true?? I have used some 2 stroke in this engine, adjusted the needle valve a little and it ran great. The guy I got this engine from said he had it for a long time. Thinks it is the series 1. I can send it in if you think it needs some Pro TLC.
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Old 03-30-2011, 05:47 AM
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Bax
 
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Default RE: OS 120 Surpass FS Series

You may want to try a new glow plug, you may want to check the rocker arm/valve clearances. If the engine has had a lot of use before you got it, it may be wearing out, and you may need a new piston ring at the very least. If it's running well, you may just want to leave it alone.

The first signs of an engine wearing-out its compression fit is an idle that's deteriorating because of the lowered compression.
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Old 03-30-2011, 11:54 AM
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W.P. Hurst
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Default RE: OS 120 Surpass FS Series

It has good compression, and I did put another glow plug in. The glow plug was not a four stroke plug and when I removed the hot shot the motor quit. The valve clearances are about .05 mm. Is this the series 1? Do you have a link for the piston ring?
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