I have a john deere f725 front deck mower with a kaw liquid cooled twin cly motor. It seems to have a high speed flutter after a little bit of mowing almost like it is running out of fuel. I have replace filter fuel lines cleaned carb fuel pump is new.. I put in a plug adjusted the valves. Still seems to flutter when the rpms are up... help me please

You might check your gas cap and make sure its venting,and make sure there's no tight bends on your fuel lines,

We did a leak down test on the cylinders and one has 70percent leak I could hear it out the exhaust.. could this cause the flutter? And dying out?

Yes it could ,you might pull your valve covers and check your cleanrance

I have done that.. just wasent sure if a leaking exhaust valve would cause it to run like that..

Valve could be sticking.something I've found that works real good for sticky vales is SEA FOAM,you can get at about any auto parts place ,