Need help with tractor engine

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  #1  
Old 04-11-19, 08:17 PM
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Need help with tractor engine

I have a1995 Lowe’s lawn tractor with a 18hp Briggs and Stratton engine. The engine runs great when the mower is engaged. If the mower is not engaged then the engine pops and backfires badly. Any ideas on what this could be? What would cause it? Thanks in advance.
 
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  #2  
Old 04-12-19, 04:13 AM
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Have you set the valve lash? After that would be a carb cleaning and new plugs, air filter, and check for exhaust obstructions.
 
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Old 04-12-19, 08:29 AM
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I would start with the simple stuff, fuel filter,spark plug, fresh gas, try some Seafoam in the fuel system,I have had good results with it.
Geo
 
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Old 04-12-19, 09:24 AM
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There is nothing wrong with the engine because you state it runs fine with the mower engaged and doesn't run fine with mower disengaged. I would look for a defective interlock switch if mechanical engagement or defective on/off switch if electronic engagement
 
  #5  
Old 04-12-19, 07:07 PM
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That's a carburetor problem. Clean the carb, I'm assuming this is a twin opposed cylinder engine? Does applying partial choke help?
 
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Old 04-13-19, 04:45 AM
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Cheese; I thought a carb operates mainly based on RPM. Why should a change in load at constant RPM affect carb operation? The OP says he disengaged the mower but nothing about manually changing the engine RPM.
 
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Old 04-13-19, 10:09 AM
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RPM's aren't everything. An engine with no load can run at full rpm while at partial throttle which brings into play the low/idle part of the carburetor. When running at full RPM with a load the engine is closer to full load so the carb is opened up and operating mainly off the high speed jet.
 
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Old 04-13-19, 04:15 PM
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What Pilot Dane said^. The engine can reach 3200 rpm with the throttle barely cracked under no load, but under full load, it has to open further, changing the volume of air and the fuel circuits it pulls from.
 
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Old 04-13-19, 04:32 PM
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Pilot Dane: I agree that full RPM can occur anywhere in the span of throttle lever travel (since its normally adjustable). I think the OP needs to tell us if he is changing the throttle lever position after disengaging the blade and experiencing poor engine operation. His post doesn't state either way. I assumed he was not changing the throttle lever position.I also know the non-Webster definition of assume.lol
 
  #10  
Old 04-14-19, 02:30 AM
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I wouldn't think the throttle position is being changed, the governor is changing the throttle position on the carb itself, not the throttle cable. I see this often... I had one yesterday that was sputtering and surging no load but ran just fine with the blades engaged or even driving in gear. It was the carburetor.
 
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