musltang

as far as i know my engine is an os surpass 120 pump II. it runs great for a minute or so then it starts to sputter. and eventually dies. i have designed my fuel system exactly as os described in my manual. i also replaced all the fuel lines twice now. still the same problem. anybody have a simular experience. if so did you ever get it to run correctly. please help

Richard L.

My Feedback: (24)

Sounds like it's way too rich. With a pumped engine, you lean out the top end to max rpm and leave it there or back off 1 click only. In other words, you don't back off 200-300 rpm like you normally do on non-pumped engines. In the air, the pump will provide plenty of fuel flow. Also, try a fresh new Type F glow plug.

Richard L.

My Feedback: (24)

Make sure that your engine is pumped. You should see a pumped mounted at the rear of the engine, and the muffler should not have a pressure fitting. The vent line from the fuel tank should not be hooked up to anything and should be vent to the atmosphere.

Bax

My Feedback: (11)

Here's how to set up your pumped O.S. engine:

http://www.osengines.com/faq/faq-pumped.html

If you need the instructions, please send an email to the address below, asking for the instructions for your particular engine...in this case, the O.S. FS-120 Surpass II (it has the pump with no adjustment screw, and the carburetor is the #C13 with the velocity stack).

musltang

i pulled the carb and discovered how to lean the idle mixture and also gave it a good inspection. after cleaning and sealing everything up I ran it to find that it does the same thing. this time i had the cowl off. I noticed fuel is leeking from the back of the carb. I think the part is called the mixture control valve. I just replaced the o-rings inside it, so im gonna cross my fingers because the mixture control diaphram is out of production.

SDR-Hammer

I’ll give you my experience with this exact same engine and do what you want with this info.

I bought it from a guy at a really good price because he could not get it running right. The engine had been back to O.S. for I believe three times. Every time the engine came back with a tech report that stated the engine performed with no problems.

I put a pressure tap on the muffler and now run it without the pump. I wasn’t sure what was going to happen to the pump without being lubed with fuel. Since it’s connected to the crank I certainly did not want it seizing up. After filling the pump with a light oil I took a short piece of fuel line and created a loop between the pump’s inlet and outlet.

Bax may come back to say that to run this engine without a pump you need a differnt carb, crank and back plate.

So far I've run about a gal of fuel in this configuartion and it has performed extremely well in a 3-D plane. Had one dead stick when the muffler pressure line came off.