I own a John Deere F735 with the V-twin Yanmar diesel 20 HP engine in it. It has 1200 hours on it and the oil has always been changed at 100 hr.'s every time! It has run strong and sweet singing since day one. Recently I had the water pump seal replaced. After getting it back I noticed it was short on the top end. OK - easy, just adjust the throttle cable a bit again and I'll get the RPM's back up. NOPE - It was maxed out already and It seems I've lost 5% - 20% of my top end toruqe. I run a mulcher on it and I know how it sounds and acts in different lengths of grass. I've also noticed after I turn it off for 5 minutes and start it back up, I can floor it and it blows black smoke and and takes a bit to get up to RPM's like it's under load. I was told he had to pull the motor up off the frame to change this seal out. Now what the heck could he have done to it in order for these new symptoms to start??? I tried injector cleaner but didn't seem to work. Cleaned the air filter and the hydraulic fluid was changed out not too long ago. Do I need new injectors, is one plugged?????? This is my first diesel and I bet other members here have had similar experiences with the way my engine is acting up. Any help greatly appreciated - I'd like to be informed before I have this tech try and figure it out on my wallet!