Murray mower won't stay running

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  #1  
Old 02-03-10, 05:25 PM
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Murray mower won't stay running

Hello,

I was given a Murray mower that sat outside (California) for a few months. The guy said it ran good and always started on the first pull.

I cleaned the carb well with carb cleaner and it looks pretty good. It primes well. It starts on the first pull but only runs for 3 or 4 seconds and dies. Sounds good while it does run.

Any ideas?

Thank you very much.
 
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  #2  
Old 02-03-10, 05:39 PM
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Please post the engine manufacturer, model, type, code etc. usually found on the engine shroud just above the spark plug. Have a good one. Geo
 
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Old 02-03-10, 05:53 PM
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Thanks Geo

All I can find is model number 21735X62A and Murray Ohio Mfg. Co. It's pretty old.
 
  #4  
Old 02-03-10, 06:27 PM
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I found it, it was covered up.

Model Type Code
127802-1109-01 9411295
 
  #5  
Old 02-03-10, 07:18 PM
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Make sure the holes in the bottom of the bowl nut are clean, this is the main jet. Have a good one. Geo
 
  #6  
Old 02-04-10, 03:24 PM
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Ok. It's running now. Thanks a bunch. That's a weird place to find a main jet. How does that work?
 
  #7  
Old 02-04-10, 06:22 PM
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Heck, I don't know it works, I just know how to fix them, I think it has to do with engine pulse and stuff, the combination of the engine pulse pressure in the carb bowl pushing fuel up the emulsion tube and the vacuum of the intake presents the fuel mist to the engine, which if, compression and spark are also available will create smoke and noise. The jet is at the bottom so as to give it the greatest opportunity to pick up fuel. I am sure one of the real mechanics will correct my errors. Have a good one. Geo
 
  #8  
Old 02-04-10, 09:08 PM
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Well, if you can fix it then that's good enough!

What about drive cables? This mower has a really frozen drive cable. Are the drive cables for these readily available or is it too old? I haven't been able to find any online so far.
 
  #9  
Old 02-05-10, 12:39 AM
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The cables should still be available from briggs. Look for a number stamped into the cable housing.
 
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Old 02-05-10, 06:06 AM
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Originally Posted by asker7 View Post
Ok. It's running now. Thanks a bunch. That's a weird place to find a main jet. How does that work?
The Venturi effect is a special case of the Bernoulli effect, in the case of fluid or air flow through a tube or pipe with a constriction in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli effect. It is named after the Italian physicist Giovanni Battista Venturi.
In the case of the carb the "restriction" is the venturi or hour glass shape of the carburetor throat.

If you were to put a straw or hose into a glass of water and blow air over the top or open end, you can see the water rise in the straw...

Some primers work by pressurizing the bowl to force fuel into the throat, however the engine pulses should not pressurize the carb.
 
  #11  
Old 02-05-10, 06:42 AM
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Originally Posted by geogrubb View Post
, compression and spark are also available will create smoke and noise.....
There you go again, using those highly technical terms.

 
  #12  
Old 02-05-10, 06:47 AM
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Originally Posted by GlenM View Post
There you go again, using those highly technical terms.

Small engine fixiters are hi tek folks

geo-I just thought of where you might have the idea about engine pulses working in the carb. Many riders use engine pulses to operate a diaphram fuel pump, and in the case of most Briggs, this fuel pump is incorparated on the front of the carb....or
the recycle vent from the crank breather to the air filter housing, which has no affect on the pressure of the bowl.

And just for extra FYI fun facts, these are the exact same physics that allow and airplane wing to create lift Beer 4U2
 

Last edited by BFHFixit; 02-05-10 at 09:23 AM.
  #13  
Old 02-05-10, 12:56 PM
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Originally Posted by asker7 View Post
Well, if you can fix it then that's good enough!

What about drive cables? This mower has a really frozen drive cable. Are the drive cables for these readily available or is it too old? I haven't been able to find any online so far.
based on engine numbers it's 1994
 
  #14  
Old 02-05-10, 04:44 PM
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Originally Posted by BFHFixit View Post
Small engine fixiters are hi tek folks

geo-I just thought of where you might have the idea about engine pulses working in the carb. Many riders use engine pulses to operate a diaphram fuel pump, and in the case of most Briggs, this fuel pump is incorparated on the front of the carb....or
the recycle vent from the crank breather to the air filter housing, which has no affect on the pressure of the bowl.

And just for extra FYI fun facts, these are the exact same physics that allow and airplane wing to create lift Beer 4U2
All of this air pressure stuff is scary for an old guy like me, it's sorta like electricity, you can't see it, and that's spooky, you know you cant blow a ping-pong ball out of a funnel with a high pressure hose if you start slow, boggles the mind. Have a good one. Geo
 
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