Thanks John; great information. My mower's a 43SL with a square oil drain plug (horizontal) and an angled filler plug (plastic) both on the back. I can find no dip stick - front or back so how do I judge the correct oil level? Where should the (missing) wavy washer be located on the throttle assembly? There's a trapezoidal opening and spigot hole in the housing on the right side. Is it there? There's no sign of anything having been mounted axially & I haven't taken it to pieces and lost anything.

Alan, June 2009

Hi Alan - I'm thinking now that your engine is painted black...in which case the oil level is correct when you take out the 2 pronged filler plug and add oil until it starts to run back out - making sure the machine is level, of course.
As for the throttle linkage, the fault must be in the control lever on the handlebar....maybe something has broken in here? Trouble is, I cant for the life of me remember what the thing looks like - sorry!

John, June 2009