Engine Starting Problem

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  #1  
Old 05-12-03, 11:40 AM
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murray pushmower

Ok. Here's another question. My grampa also has a 25 year old murray push mower with a briggs engine. It won't start unless I pour gas into the intake. I replaced the diaghragm (the type that just has one diaghragm with a spring connected to it with a small rod that connects to a butterfly valve) and used compressed air to blow out every hole and passageway in the carburetor. I set the needle valve so the engine runs smooth when hot, but I can't start it cold, I can start it while it is still hot. When I had the air filter off, it would run at about 3/4 full throttle, even though the throttle was wide open. And if I put my hand over the intake for a second, It would speed up to a normal sounding speed. It seems that the carburetor can't siphon enough gas so it would run wide open. Plus when I slow the throttle down, there is barely any change in rpm from wide open to idle, then if I keep pulling the throttle back all the way, that is the kill position. Why won't it start cold? Why is there barely any change in speed no matter where the throttle is? Thanks for the help.
 
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  #2  
Old 05-12-03, 10:35 PM
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Sounds like you have either: more carb problems, a missing O-ring at the carb mount, or a bad intake tube. Another possibility could be an intake valve needing adjustment.
 
  #3  
Old 05-12-03, 10:37 PM
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What should the intake valve be set at. It did look a little tight.
 
  #4  
Old 05-12-03, 11:15 PM
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I don't know what engine model you have, but .005" should be ok.
 
  #5  
Old 05-13-03, 03:54 AM
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Here's a simple idea (at least to me).

With the engine stone cold, squirt a little fuel into the cylinder. If it fires right up when cold, I would say it's still a carburetor problem.

Just an idea.
 
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Old 05-13-03, 10:56 AM
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Mower is doing that already to start the engine (stated in his original post).

Trouble with that is that if the intake valve has seated far enough into the seat that it makes the stem to tappet clearance too small, it will still run with pouring gas into the carb. The problem, if it is a valve clearance issue, is that the engine does not develop enough negative pressure at the carb throat to pull gas in through the carb at low RPM (such as starting). I've seen it several times.
 
  #7  
Old 05-13-03, 03:48 PM
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Thanks Mr. Cheese, you are once again a genius. I checked the intake valve and I couldn't fit the .005" feeler guage so I ground the valve stem enough so the feeler guage would fit easily. I put everything back together, gave it a little throttle, and it started on the second pull. I didn't even touch the carburetor. I was so happy and my gramps was also very happy. Thank you very much.
 
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Old 05-14-03, 12:13 AM
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Good job! I had a feeling, because of the detailed description of the problem you gave, that it was a valve problem. Glad to be a help!
 
  #9  
Old 05-14-03, 11:05 AM
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Mower:

Good job! It's a lot of fun and satisfying to fix something like this, isn't it?

I had a good laugh at my "broken" snowblower that was given to me and cast off for no good.

After some TLC it fired up on the 4th try. Who knows when it was used last! .
 
  #10  
Old 05-14-03, 12:54 PM
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Joe_F, you are right. Fixing old things that someone throws aside because they don't understand the problem is like waking up on christmas morning, you get useful toys for almost nothing, and many times the things they junk are still good. Plus the joy of knowing you fixed it. And then working as a parts guy has a major plus side, especially when other dealers say you can't get the parts anymore and you need them soon. Congradulations with the snowblower.
 
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