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O.S. 1.20


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Rob Harrison12/09/2008 19:41:00
1 forum posts

Hi I got a os 120 fourstorke pumped any I dears on setting up the thank to run thought the pump.


Bruce Richards12/09/2008 21:12:00
1849 forum posts

I have the same engine and my setup is

  • clunk in bottom of tank going to pump IN
  • pump OUT to top of tank with Tee to a pipe with fuel button
  • fill to bottom of tank with fuel button in pipe

So to fill tank take out both fuel buttons and fill through fill pipe until fuel comes out of other pipe

To empty take out both buttons and suck out through fill pipe.

I have been running with both fuel buttons in but wondering if the fill should not be sealed to provide air to replaiceburnt fuel.

I have had a few dead stick and this could be the problem anyone else throw any light on this?

Engine Doctor14/09/2008 12:14:00
2466 forum posts
39 photos

Hi . What mark of 120 pumper do you have? the Mk 11 and Mk111 both require different plumbing. The Mk 11 has the pump , a mechanical gear type of pump, mounted on the back plate .It is fitted with three fuel nipples .Fuel in (from tank) fuel out (from pump to carb ) And fuel return (this is for excess fuel to return to tank.)Make sure this is not kinked or restricted . I usually fit a slightly larger diameter fuel pipe to this as any restrictions can cause the motor to throw a prop, not very nice ! The mk 111 just has the one fuel pipe nipple and no fuel return pipe ,  The pump is a diaphragm type and is integral with the carb it  has a short pipe conecting it to the crank case for Crank case pressure to operate the pump. No exhaust pressure is required with either type . Plumb your tank as normal for clunk and fuel fill/empty pipes . Both types MUST have a fuel tank breather to allow air into the tank as fuel is pumped out . Failure to fit this breather will cause the engine to cut out after a short run. Both engines are superb and once set up require little or no messing. DONT be tempted to strip the pumps down unless your are confident and up to it as the earlier pump has a pressure release adjuster screw , once messed with it will take ages to sort unless you really know your engines. The beuty of these pumps is that you can fit your fuel tank further back over the Cof G so that you get a constant trimm setting unaffected by the weight of the fuel.

Hope it helps


Bruce Richards14/09/2008 18:33:00
1849 forum posts
Ah yes in my description I assumed the pump to carb line was in place as it was on mine when I got it. Sorry for any confusion this may have caused

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