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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 28106
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a mower with an FH580V engine that has a slight miss.

Customer Question

Hi, I have a scag mower with an FH580V engine that has a slight miss. If I run it at partial choke it smooth's out and runs better. Spark plug check shows the left cylinder is running leaner than the right. Compression on the left side is 15 lower than the right and they are 100 and 115 respectively. I have been running seafoam in it hoping it would clear up but that has not made a difference. Carb issue? 400 hrs. on the engine and it has always run good, unfortunately I was not using it when the issue developed so I'm not sure how or why it started.
Submitted: 1 year ago.
Category: Small Engine
Customer: replied 1 year ago.
Correction slight miss at WOT, anything less than 3/4 throttle and it struggles to maintain a constant rpm. Also, I did change the fuel filter and have just now removed the carb and cleaned but still running the same.
Expert:  Curtis B. replied 1 year ago.

Have you checked the valve lash?

Expert:  Curtis B. replied 1 year ago.

FH580V0 .004 / 0.006 inch,

Customer: replied 1 year ago.
No, i will do that tomorrow evening. Thanks.
Expert:  Curtis B. replied 1 year ago.

OK, try that, Next I would be sure I have good spark to both cylinders.

Customer: replied 1 year ago.
I have not had a chance to get to the valves yet but when I do I will let u know. Both spark plugs indicate good spark and I have been mowing on part choke for 4 months so i think it is safe to assume spark is good but I will get a new set of plugs too. I will comment on you once we figure it out..good day.
Expert:  Curtis B. replied 1 year ago.

OK, thanks