Small Engines (Lawn Mowers, etc.): riding lawn mower, clutch adjustment, clutch pedal

Question
hello,i have a 1986 ranch king which i installed an 18hp twin 2 engine the problem i'm having is when the mower is on an incline the engine spits and sputter and emits black smoke but on level ground the engine runs fine.
problem 2-whith the engine on and the clutch pedal pressed i can't shif grom forward to reverse but when i shut the engine off it shifts fine.  joe

Answer
Your first problem (black smoke on incline) is most likely related to the float level being a little too high and the incline causes a flooding condition.
The second problem is likely related to the drive belt adjustment and/or the brake mechanism.  If the transmission can't be disengaged from power (belt not loose enough when clutch pedal pressed or brake on transmission not stopping movement of machine) it cannot be shifted.  These are not synchronized transmissions so they need to be, at least, momentarily stopped to all them to be shifted.  Check the belt / clutch adjustment first.  Hope this helps.