Kawasaki stumbling on acceleration

[Scrubcadet10]

Friend has a Kawasaki FE290D-DS20
In a Mule, he says it idles great, but on acceleration it stumbles but then once he gets to high rpm, it runs great.
Brand new OEM carb, New magneto, New plug.
I've sent him Info on The pilot screw adjustments etc.
Any One think of anything else?

 

[bertsmobile1]

Blown head gasket.

 

[mechanic mark]

check air filters for replacement.