Lucius1958 wrote:That's a Model B.
First of all, have you cleaned the motor and upper works yet? If not, you should do so. Remove, clean, and reinstall the mainspring as well, lubricating it with a good grade of grease (lithium or molybdenum are good). The rest should be lubricated with fine sewing machine oil.
If it still bogs down, you can adjust the pressure on the half nut, using the screw on its spring mount: alternatively, check the mandrel bearings on either end, and adjust them until it runs properly.
Bill
Seriously, is it really good advice to a novice to remove the mainspring?
Raphael