12 HP mower runs fast

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  #1  
Old 08-13-04, 06:33 PM
scarrol1
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12 HP mower runs fast

I have a 1987 MTD 12 HP mower with the I/C engine. The Engine model is 281707 and the type is 0137. I recently replaced the head gasket and after doing so I noticed that the engine was racing at full speed. I tried to adjust the carb without any change. When I took apart the carb I found that there was a crack in the case. I bought a new carb from briggs and stratton and installed on the mower. The problem is that the mower continues to runs at fast idle. I followed the instructions for adjustments on this site. I adjusted the idle speed from closed position out by 2 full terms. I then tried to adjust the bowl screw. I can tighten the bowl screw (cw)all the way closed and the engine still runs at high speed. I can turn the screw CCW and the engine will stall at about 3 turns. In addition, the lawnmower is sucking down the gas. It used a gallon of gas in about 20 minutes of use. I took out the spark plug and cleaned it. I also pulled the fuel filter and cleaned. I am going to the store and purchase a new muffler as my current muffler keeps falling off because of the excessive vibration from high speed. The spring governor link is broken but everything else is fine. Could this be the issue?

Thanks .
 
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  #2  
Old 08-13-04, 10:27 PM
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sounds like throttle plate is stuck open because linkage is not hooked up right. take off breather and look at throttle plate move cable to idle position, throttle plate should partially open. i am betting its wide open.
 
  #3  
Old 08-14-04, 12:22 PM
scarrol1
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nothing wrong with the throttle. any other suggestions? I replaced the spring that was missing from the throttle, put in a new spark plug and new fuel filter. Still same issue. Runs like it is in a race and unscrews the muffler after about 15 minutes.
 
  #4  
Old 08-14-04, 03:39 PM
Azis
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Until the problem is solved, ya may not want to run it long enuff for the muffler to come off...
Only start it after making changes to see if the problem is fixed. It may be a leak on the intake, since you recently replaced the head gasket, that would be a good place to start looking. You may also be able to run it for a short bit while spraying carb cleaner in suspect areas, Listening for a change of tone in the engine.
 
  #5  
Old 08-14-04, 07:37 PM
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agreed.if linkage ok. has to be vaccum leak.
 
  #6  
Old 08-15-04, 01:31 AM
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It's pretty common on those engines for the governor to come apart internally. Replacement of the governor is usually all that is required, unless the engine has run wide open long enough to ruin the rod and other parts.
 
  #7  
Old 09-05-04, 07:32 PM
scarrol1
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Thanks. Turned out to be the governor. Also in the process, I found that the screw type muffler that was on the lawnmower when I purchased it used, was not the correct muffler. Replaced with a muffler that bolts to the motor and it works fine.
 
  #8  
Old 09-08-04, 12:28 AM
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Great! Glad we could help!
 
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