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bgsengineclinic, Small Engine Technician
Category: Small Engine
Satisfied Customers: 220
Experience:  Over 20 years of experience in Small engine repair, Kohler Certified Expert Technician, Self-Employed in my own dealership.
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i have kubota diesel lawn tractor that has a rough idle but

Resolved Question:

i have kubota diesel lawn tractor that has a rough idle but runs perfect at any rpm above idle, wondering were to start and what to test
Submitted: 5 years ago.
Category: Small Engine
Expert:  bgsengineclinic replied 5 years ago.
OK how is the air filter on this unit? Has it been serviced and cleaned out? Sounds like an unclean fuel filter replacement procedure was done, potentially allowing dirt into the fuel pump or injectors - how bad is this rough idle?

Have you tried a diesel injector cleaner in the fuel yet? That can *sometimes* help.
Why was the fuel filter replaced?
Customer: replied 5 years ago.
air filter is new, fuel filter was installed by local dealer and was replaced due to hours on machine. i have not tried any fuel additives yet. the lawn tractor shakes pretty bad almost as if it has misfire and as soon as you take it off idle it runs perfect. is there any way to test the injectors or plugged fuel line with out any special tools
Expert:  bgsengineclinic replied 5 years ago.
Hmm OK it is just at dead idle.. I would be wondering about fuel quality, water in fuel, low line pressures, as well. No way to test injectors without special tools , as you need a injector test bench to check flow and spray patterns - it probably *is* a misfire - at idle it would be delivering so little fuel due to a restriction in injector nozzle, it may be a lean misfire .. one way that may be possible to detect this is with an infrared thermometer, and measure exhaust temperatures at each exhaust manifold - but again thats generally not a tool most homeowners will have. If it has not been more than 90 days or so since the dealer service, I might recommend contacting the dealer and see if they will warranty it - if the tech was not clean and got some dirt in the filter or fuel inlet to the pump, it can take a while for dirt to migrate through the system.

It is not really something your average handyman would be able to diagnose effectively or repair. and I would recommend talking to the dealer that did the service work, and see if they will check it out for you, as if the tech made a mistake, I'm sure they will want to rectify it.
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