Motor is running eratic up and down under load

One of the most important parts of your engine is the engine governor. An improperly adjusted governor can shorten your engine's life. If engine speed is not controlled, the engine will destroy itself. Never run an engine over speed, especially without a load attached to it. Even for a short period of time it can cause catastrophic failures, like blowing the magneto magnet into 100's of little pieces. Over speeding is something that needs to be taken care of immediately, because it can be a real hazard with metal coming loose at high speed. This page will explain how to adjust the mechanical governor on Briggs and Stratton and Tecumseh Engines.
First, let's understand a little more about governors and why they may not be working right:
Most complaints about governors fall into two categories:

1. Engine runs too fast or too slow.
2. Engine surges or hunts.

You should do an inspection of the governor linkage and spring before trying to solve either of these problems. Make sure everything is operating freely and the spring is not damaged or stretched. Also, check the governor static adjustment to see that all free play has been removed between the spindle and carburetor. The best way to do this is to move the throttle from idle to full open and note the way the governor shaft moves. If it goes clockwise, then loosen the clamp screw and with the throttle wide open turn the shaft all the way clockwise and re-tighten the nut. Make sure the throttle moves from idle to full open freely after making the adjustment. Refer to the engine repair manual for exact adjustment procedures.
After you have made the above check, restart the engine and see if the governor now operates correctly. With the engine at idle, move the governor lever with your finger to open the throttle and it should push the arm back toward idle if working properly. One way to do this test is with the governor spring removed. If it still over speeds or has no push toward idle, you probably will need to have the internal parts checked inside the motor or recheck the static adjustmen