I think I read somewhere on here that they where the same except for a couple slight alterations like the air cleaner and one other thing,,the insides are pretty much the same with cast iron sleeve from what i read...who knows,only time will tell for meI didn't mean to imply that fs and fr engines are identical except for air cleaners I was asking if they are....
UPDATE..
From Kawi web site looks like the only difference is the air filter to me..
FR Series Professional-grade power gets personal
Overhead V-valve
90° V-twin design
High performance pressurized lubrication
Electronic spark ignition
Automatic compression release
Single stage air filter
Cast-iron cylinder liners
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FS Series Rock solid foundation for turf work
Overhead V-valve
90° V-twin design
High performance lubrication system
Electronic spark ignition
Automatic compression release
Dual element air filter
Cast-iron cylinder liners