OS FS-20 Four Stroke

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OS FS-20 Four Stroke

Postby stewbow » Sun Feb 20, 2005 7:52 pm

I have just resurected a twenty year old OS FS 20 Four Stroke. It as completely frozen up, but by disassembling and soaking it in penetrating oil, I got it to turn over smoothly. The biggest problem was freeing up the tappets, as the cams were hanging up on them.

The engine started right up and runs fine at full power. The only problem is that when I throttle back to half power or so, the engine will only run for about five seconds and then lean out. I noticed that when I disassembled the carb that there appeared to be white silicon sealant around the rotating barrel on the throttle arm side of the carb. I suspect that I may have to replace the sealant to keep out air which apparently is causing the engine to kill lean.

Does anyone have any thoughts? Thanks. Stewbow
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Postby propwobble » Sun Apr 17, 2005 11:20 am

Stewbow,

I don't recall silicone sealant being a normal part of any OS carb. Air leaking in from around the carb barrel sure could cause a lean run but I don't think silicone sealant is an adequate solution. Sounds to me like the throttle barrel or carb body or both is worn. There should be no appreciable radial slop between the barrel and carb body it rotates in. Overhaul or new carb time if there is.
Cam
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Re: OS FS-20 Four Stroke

Postby Ed Cregger » Fri Mar 24, 2006 5:18 am

stewbow wrote:I have just resurected a twenty year old OS FS 20 Four Stroke. It as completely frozen up, but by disassembling and soaking it in penetrating oil, I got it to turn over smoothly. The biggest problem was freeing up the tappets, as the cams were hanging up on them.

The engine started right up and runs fine at full power. The only problem is that when I throttle back to half power or so, the engine will only run for about five seconds and then lean out. I noticed that when I disassembled the carb that there appeared to be white silicon sealant around the rotating barrel on the throttle arm side of the carb. I suspect that I may have to replace the sealant to keep out air which apparently is causing the engine to kill lean.

Does anyone have any thoughts? Thanks. Stewbow




It has been a decade since I ran my OS FS-20 (now sold), but I do seem to recall seeing something white around the throttle barrel. Maybe not.

I would think that OS would use an o-ring, rather than relying upon applied sealant.

One thing to do would be to go to the Tower Hobbies site and look for an exploded view of the carb.

My OS FS-20 was one of the sweetest engines that I have owned in over fifty years of modeling. Good luck solving the problem.

Ed Cregger
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