pbeck

I have an os 50 which up to recently has run well. Recently it was stripped down, cleaned and reassembled. Initially it ran well. However lately the following has occurred. Prior to starting, a little fuel is squirted into the intake, the prop turned over and then the glow plug battery is applied. Presto, the engine fires up, runs briefly then stops. A fuel problem obviously as no fuel appears to be or is being drawn into the engine from the tank. All components,engine, filters, tank etc are removed, thoroughly cleaned and the system tested on a test stand. The problem remains:- The motor starts effortlessly, runs for a few seconds and dies. No amount of adjustment seems to fix it. What is causing this???

Thank you.....pbeck.

FHHuber

Take the needle valve assembly apart. You have something in the needle. (you didn't say you cleaned that...) There can be a TINY bit of something n the needle which you can't even see (because of where it is...) will block fuel flow.

You could also have developed an air leak under the carb... or the backplate gasket could be leaking. (or both) but generally... that means you just get a lean run at low throttle... and have the ability to run OK at high throttle with the needle about 1/2 turn open from normal.

You could also have somehow closed down the idle needle too far durring carb reassembly... (but it wouldn't have run fuel from the tank at any time like that)

Pinched fuel line? (sometimes its just so simple... its sick. [img]i/expressions/face-icon-small-tongue.gif[/img] )

pbeck

Thank you for these tips. I have thoroughly cleaned that needle valve and did check it and its asembly thinking that was most likely the cause. As you correctly say, it has to be a pretty basic thing. Very frustrating. Will keep trying with it. That idle adjustment may be a factor.

pbeck

Amazing. I have recleaned the needle valve plus the assembly, checked the tank plus the lines, but I am now completely stumped:- The same problem remains. I guess the next step is take the blessed thing to an engine expert!!!

RaceCity

Huber was right the first time. Something is blocking the fuel flow.


Here:

1) Open the needle valve a few turns/have throttle wide open.
2) Attach a clean piece of fuel tubing to the fuel fitting on the carb.
3) Blow air into the fuel tubing...it should flow freely...you should hear a "hissing" noise inside carb.

A) Air flows freely? No blockage.
B) No air flows? Something is clogged in there.

PLAN B

Blow into the vent line of the fuel tank....air should flow freely out of the fuel feed line, if not, there is a blockage or the fuel line is pinched someplace.

In either case...it should be a simple fix. Doesn't sound like a mechanical problem with the engine at all.

'Nite

jgs77

My Feedback: (1)

pbeck,

I have the solution.... Sell me that engine. I've been searching high and low for that O.S. 50. Loop scavenged, with offset glo-plug and dorky looking muffler with only one screw; is that the one?

Greg

ballgunner

My Feedback: (1)

There is a fairly common problem with Magnum 4 strokes with the small "O" ring where the needle enters the carb fuel inlet. When disassembled it may look just fine but the idle and in air perfomance is marked by surging and unplanned shut down. The original "O" ring seal will last for many hours and then suddenly - problem. I don't know if that assembly even resembles the OS.50 but if it does it might be worth a try. You are definitely getting a lean out from lack of fuel or an undetectable air leak.

maxtenet

Who reassembled it? sounds like it may have the sleeve in backwards. Spin it and retry.

max