# Oscillating Throttle



## Grant_34 (Aug 24, 2010)

I am trying to repair a Honda HR 173 lawn mower, with a GV100 K1 engine.

A week ago it seemed to run fine. I then refilled it with some more fuel.

I tried it on Sunday and it had developed a burp every couple of seconds.
The spark plug was black and dry, so I replaced this with a new one.
I emptied the old fuel and refilled it with new. 
Checked the air filter, Fuel filter and checked the oil was “clean”, all seems fine.

After some “checking” of the Pilot Screw, Throttle Stop Screw & Stopper Screw the lawnmower starts then the Anti-Surge Spring and Throttle oscillate and then the engine stops after about 15 seconds.

Any ideas? I'm stumped!


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## Grant_34 (Aug 24, 2010)

P.S. I have had it on its side before I got the service manual saying "Don't put it on the side of the carburettor”! So after that I then drained the oil and replaced it. I have not taken the Carb off and was reluctant to do so because I do not have replacement gaskets. It has run after this but with the symptoms above.


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## 30yearTech (Sep 14, 2006)

The reason you don't want it on it's side with the carburetor facing down, is because the crankcase vents into the air filter chamber. When in this position oil from the crankcase can flow into the air filter and contaminate it. 

Try running the engine without the air filter element and see if there is any difference in the way the engine runs, just don't use the mower this way. If it runs good without the air filter, then you need to replace the element.


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## Grant_34 (Aug 24, 2010)

Hi 
Thanks for the reply.

It runs the same with the air filter removed. The air filter and air filter case, looked and felt good, not covered in the black oil I drained from the oil tank. I didn't feel the need to wash it and re-oil it. (for the moment at least)


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## Grant_34 (Aug 24, 2010)

Is it possible to post a short video I have made of the syptoms?


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## Grant_34 (Aug 24, 2010)

Fixed!

I have removed the fuel line (careful) not to get squirted with fuel and drained the fuel tank into a suitable container. Removed the carbs drain screw and let the fuel drain through. Using the compressor set very low blew through from the fuel nipple.

p.s. When taking the top/fuel tank off be careful to keep hold of the three spacers and washers.

And put some light lawnmower oil into the air filter and gave it a tight squeeze.

I found the service manual very helpful.


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