The biggest issue with diesel power is weight. This is true in light trucks, and in ZTR's.
A Kohler V-Twin weighs in just under 100lbs dry.
A.... (lets use Kubota) 3cyl 1L Diesel is over 200lbs dry. Now add 3 more quarts of oil, a radiator, hoses, fans, and coolant.
Adding 2-300lbs to a 1300lb ZTR is a BIG deal.
Especially when we have some rather excellent air cooled V-Twins these days.
This Kubota Diesel is 25hp and ~45lb/ft of torque. You can get a gas powered V-Twin that will blow it's doors off when it comes to power and RPM maintaining torque.
ZTR quality continues to improve, but for the most part, a ZTR is pretty worn out after 3K hours, no sense putting a 10K hour engine on a 3Khr ZTR. Especially when the diesel is adding thousands to the MSRP.
I'd love to have a little 1L diesel that's TURBO'd to keep torque up and maintain RPM's better. Don't know why manufactures dont explore this a little further.
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2013 eXmark LazerZ X-Series 60" 34hp EFI (RED) Kohler
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1996 48" SCAG Belt WB 14hp Kawasaki Classic Deck
Echo 2 strokes PB-755 & SRM 280
Eastman WM20H 20" Commercial Push mower (NEW for 2013)
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