Motor runs what seems like slow and when you pull handle to start it rips it out of my hand

Where do you connect the 12 v battery power cable to the engine on a 4stroke 40 hp yamaha year 2005.

surging when running is most likely normal ,they have a governer that control's the carb & rpm so it wont over rev. It has a paddle near the fly wheel to pick up wind from it when running hooked to the carb with a small lever and held stable by a spring. Check to see if the spring is too tight or sloppy. 8 hp is a pretty big motor and a kick back is not really un expected. But a plastic handle is kinda cheesy, a rubber or a wooden handle would be better.Good thing you have electric start!

The string assembly should reach a point far enough out when you pull the cord that it lets it spin free of the engine. What you are probably experiencing is the engine kick-back, where the engine is compressing the air/gas in the cylinder, and the pressure pushes the engine back. The crankshaft is connected to the pull cord assembly, so it's pulling out of your hand. You may not be pulling hard enough, or the cord assembly needs replacing.

This seems like the key-way is gone underneath the fly wheel. I hope this will help a bit.

honey it seems as thou your compressor has lived its life and is just tired

DID WE CHANGE THE MOTOR ? THE BLADE ON A LAWN MOWER ENGINE IS THE FLYWHEEL. IF NOT IT SOUNDS LIKE THE KEY IN THE FLYWHEEL IS SHEARED , THIS ALSO WILL CAUSE THIS PULL CORD ISSUE... .. IF'N I WAS ANY HELP VOTE FOR ME ...THANKS.. JAY

Look instead at the motor and drill post bearings. Remove the belt to see if the motor runs correctly with no load. If it still hums and gets hot, check that the motor itself turns freely (when off). If the motor seems to be ok, turn the driven pulley by hand--it should also turn freely. The capacitor is usually a starting assist, not running. To test, wrap a small rope several turns (when pulled must turn in the normal direction) around the small motor pulley and pull smartly while turning the motor on. If it now comes up to speed, the capacitor has lost capacitance. Electronic parts suppliers like Jameco or Mouser have such items.

sounds like timing issue check the flywheel key and see if it sheared. could be the valves also but i doubt it.

Sounds like the run capacitor has given up. Or, maybe the worst is it overheated and burned the motor winding. You'll probably have to take it apart. If there is a smoked capacitor, that's probably the one you should replace. If the winding is scorched, might as well get a new motor. If both are the case, then replace the capacitor before you give up on the winding.

These motors were famous for the seal sticking to shaft. If this is an older unit turn the fan on motor by hand until it breaks free. Do this with power off.