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    OS 120 w pump - 9/14/2010 10:57 PM   
    vmosmith


     

    Posts: 5
    Score: 100
    Joined: 12/11/2007
    Last Login: 11/8/2012
    From: Wesley Chapel, FL, USA
    Status: offline     		My used os pumped 120 wouldn't idle or transition, so I bypassed the pump and am now running it with muffler pressure. It seems to be working. Anyone else have a similar experience or any thoughts?

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    RE: OS 120 w pump - 9/15/2010 12:01 AM   
    Campgems


     

    Posts: 4439
    Score: 138
    Joined: 2/18/2006
    Last Login: 5/17/2013
    From: Arroyo Grande, CA, USA
    Status: offline     		There are three different versions of the 120 Pump engine.  Surpass I does not have a regulator on the carb. It has a mechanical pump.  Surpass II has a big regulator with a metal cap on the carb, and an upgraded Mechanical pump.  The Surpass III had a small regulator on the carb with a black plastic cover and the pump is a small diaphragm pump again in black plastic. 

    Which one do you have?

    Don

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    RE: OS 120 w pump - 9/15/2010 5:29 PM   
    vmosmith


     

    Posts: 5
    Score: 100
    Joined: 12/11/2007
    Last Login: 11/8/2012
    From: Wesley Chapel, FL, USA
    Status: offline     		This is the Surpass II with the big metal regulator and the metal pump.

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    RE: OS 120 w pump - 9/16/2010 1:33 AM   
    Campgems


     

    Posts: 4439
    Score: 138
    Joined: 2/18/2006
    Last Login: 5/17/2013
    From: Arroyo Grande, CA, USA
    Status: offline     		You can replace the regulator diaphragm on that carb.  It's a little tedious and requires some solder skills but it is doable. 

    The pump seal goes out on this pump.  You will get fuel in the crank case and it is pumped up the vent line to the intake manifold.  It makes it really impossible to tune when the is is going on as you have two sources of fuel to the intake, one through the carb and one at the vent line to the intake.  My pump was in this condition.  A piece of clear vent line and the engine on a test stand showed the problem right away, you could see the fuel blubbering up the line.  A solid fix would be to replace the seal in the pump.  A bypass that seems to be working good for me is to install a T on both the carb line and the return to tank line from the pump.  Tie them together with a smaller diameter line.  This greatly reduced the pressure to the carb but still gives you the benefit of the pump.  I've been flying one for a little while now, and it is running just fine.  I'm about five tanks through it since I installed the T's.  

    You need to keep fuel going through the pump, or it is going to start eating it's self due to the lack of lubrication.  There is no easy to remove the pump and put a standard back plate on as the drive for the pump is an extension on the rod pin on the crank.  A standard back would interfere with the pin.  You could do some machine work, but you are burning your bridges and still may have a problem

    Last, I'm not sure I would trust flying with exhaust pressure on the tank with that carb.  It may run right on the ground, but in the air could be another story.  For me, the two Ts were a cheap and effective fix.  If things get worse and the engine starts acting up again, then I'll locate a replacement seal for the pump.  If you decide to pull the pump apart, watch for the tiny ball the keys the gear to the shaft.  It is really easy to loose it.  Also watch the springs so things are not fowled when you assemble it. 

    If the problem is the regulator, it is probably in the form of a leaky diaphragm.  You should be able to wad up some paper towel and put it against the hole in the regulator back plate and tell if you are blowing by fuel.  If it looks like the regulator, let me know and I'll post some photos and instructions to fix it.

    Don

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    All Forums >> Glow Engines, Gas Engines, Fuel &amp; Mfg Support Forums >> Glow Engines >> OS 120 w pump
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    More Resources on the
    O.S. FS-120 III Surpass (Pump)
  • 2 Active Classified Ad(s)
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