how do you derestict ride on lawnmowers?

Hi,

The engine is not 'restricted' as such - it is rev-limited.

If you look at the throttle mechanism, you will see that the speed control is connected to a spring. This spring acts on an arm pivoted at one end on a spindle comng out of the crankcase, and at the other end is connected to the carb throttle via a rigid link. The tension on this spring determines the maximum engine speed. Trial and error - with an accurate tachometer (I got an optical one off ebay from Hong Kong for £15) is required here.

Normally, the engine is goverened to a maximum of 3600 RPM. This can be (fairly) safely increased to 4500 assuming CLEAN OIL of the correct grade. That will give a useful increase. Any further increases in RPM will probably not live long. More power can only be had if you have access to a machine shop (raising the compression ratio etc).

Raise the gearing - you don't say what type of mower it is. Front-engined 'Westwood' type - take the drive from the engine off the deck drive pulley instead of the normal one. You may need to get creative with mounting the pulley on the crank, they won't normally invert easly. If it's a rear rider, you have 2 options - change the engine pulley as above (space permitting), and/or change the transmission output cog for a larger one. Don't overdo it - the trans has a maximum torque limit which should NOT be exceeded.

Let me know - and if it IS a rear rider and you want to sell the deck, drop me a line!

Phil Saunders
August 2008