Petrol lawn mower new lease of life

There's a terminology question here. AFAIK traditional magnetos still have two coils, the moving magnet generates a low voltage and high current in the primary which is broken by the points, leading to a high voltage in the secondary which feeds the spark plug lead.

I have always assumed that modern stuff is basically the same with, as you say, a Hall effect or similar sensor triggering an electronic breaker in the LT. Do lawnmowers, chainsaws, etc. actually have advance/retard? I guess this would be easy enough to build into the electronics.

I think you may well be right.

I don't think so.

By and large they are pretty much 'one speed' low compression engines with no particular requirement for ultimate fuel efficiency.

Does the timing of an engine need to vary at all according to the mechanical load on it, if it is maintained at a constant speed by a governor? Our mower (unlike my dad's old cylinder mower that he had in the 1960s and 70s) has a single-speed engine: the throttle control is an on/off control and does not allow the speed of the engine (and therefore the back wheels) to be varied. And the governor is surprisingly good: even when the mower encounters long or thick grass, the engine speed sounds as if it remains pretty constant - until the "digital cliff" point when the load becomes so great that it causes the engine to stall.

Dad's old mower had a variable-speed throttle - and it would be illegal nowadays on a new mower because it stayed in whatever position you set it, instead of being spring-closed so it shut off the engine as soon as you released the handle. That mower went to the tip long ago when he bought a petrol rotary mower. However I *think* his rotary mower has a similar throttle arrangement: I've a vague memory of seeing tortoise and hare logos (for slow and fast!) on a control that stays wherever you set it, with no "deadman's handle" safety device.

Our Briggs and Stratton mower has two spring-loaded handles that must be squeezed in opposite directions towards the handle: one is the on-off throttle and the other is the clutch for the back wheels. The trick is to release the clutch when turning round (or manoeuvring around flower beds etc) while still holding the throttle in the "on" position - took a little while to get the hang of that!

in principle, yes. Under light load you can advance the ignition a bit to lower fuel consumption. Think 'vacuum advance' on older vehicles

Our mower (unlike my dad's old cylinder mower that he had in

hand throttles that stay where they are are fine on ride-ons

I've never driven a ride-on mower, though when we bought our present house with a large garden, the owner offered to sell us his ride-on - luckily I spotted that his price was a real rip-off.

I'd assumed that ride-on mowers would have car-type accelerator and brake pedals, rather than a hand throttle. I've learned something.

nope. mine has hydraulic transmission, so a variable gear on the right foot and a brake on the left, but the cutter speed is constant.

If I get off and the cutter is engaged, or the brake is not applied, the motor stops

Older ones have a few speed gearbox engaged by tensioning up a belt drive.

Its only the walk-behinds that are rather safety conscious.

Mine has a car type pedal, which alows forward and reverse. Yes, there is a brake pedal too, but I've never needed to use it; just ease off the throttle.

Huh! Mine is Swedish so there is a raft of safeties including the above. Removing the rear grass collector is considered a safety issue. I have a small block of wood and a big croc clip to defeat the switch so I can blow cuttings out the back.

My walk-behind doesn't seem to chuck any grass out if the grass box isn't clipped on and therefore the stone-protecting flap is downwards. Quite what it does with the cuttings is a mystery because the amount of spoil either side of the cutting width seems to be far less that I'm cutting ;-) Perhaps it makes them disappear into thin air ;-) The instructions say "don't use without the grass box": wish we'd known that before we chose that model. All rotaries that I've used in the past have either collected grass in the box or else have kicked it out of the back without it accumulating and fouling the blade, and it never occurred to me that some might not do this. Probably some H&S rule. If I had to use a box on the back, I'd be emptying it every minute or so, given the size of our lawn and the density (as well as the length) that the grass grows.

The ride-on I used years ago had something marked as a brake pedal too. I quickly found out it had no brakes, it just worked a clutch.

NT

I had a Husqvarna rotary with a really awkward clutch mechanism. With practice I eventually got to the point where I could disengage it without either stalling it or accidentally releasing the safety handle. When I replaced it with a newer model they had changed it to a much simpler and easier to use mechanism.