Run a two stroke backwards?

I know there were certain chainsaws that this could be done on, but would it be possible on any basic two stroke! I think in theory it should unless the internals are shaped to direct fuel to the right places. This is a basic weedeater motor I'm talking about here. It's no longer a weedeater and the application I have for it would be very good if it ran opposite to what it does by design. Would doing this to test possibly cause damage! Your thoughts and discussion would be great, Thanks.

The old Gnat three wheelers used to do that for reverse gear, you'd stop the motor and start it in the other direction.

just change the ignition timing so it's a few degrees after tdc (when running the original way) then it should run the opposite way

umm...

Wont the timing be 'fixed' by being on the fly wheel with a key! How would I adjust that! Should I be able to move the coil a little bit! Cheers.

yeah is probably will be fixed, but there's a way around everything if you want to do it badly enough! Maybe get another keyway machined into the crank!

Probably easier to slot the bolt holes in the coil. I think I'll just give it a go as-is and see what happens, then worry about tuning later. Cheers for the comments.

Had an old go kart as a kid, there was an old lawn mower engine on it, if it stalled going up a hill could make for an exciting trip down when it started backwards while rolling.

had an old bike dirtbike, tried getting up a hill and ALMOST stalled it just before the top, so reved its nuts off and dropped the clutch, everything was a blur of ground and sky after that. it turned out when it almost stalled, that it had started going backwards! fun fun!

file the crank keyto adjust the timing

true but "gnats" ran a 4 stroke so spark timing must have been at or close to TDC

wont run well though as the port timing will be wrong

You jogged my memory, I had an old Jawa 125 do that to me once.

it will run but not as well. the bike that did it to me sounded a little different when it ran backwards. Also I ran a modle glow engine in reverse, it ran but was down on power.

Maybe take the barrel and head off and turn 180deg then bolt back down, then the crank will be turning the same way in relation to the barrel as it was to start with!

yes that will work rotating the barrell

UUmm, coil usually bolts to barrel !

no, to the frame

OP talking about weedeater motor, they don't have a frame (o:

Had a TY250 Yamaha trials bike that did it regularly. Could be quite exciting ( and painful!)

the problem with running backwards is that bolts will come undone as they are designed to tighten when the engine runs normal, it can be done. I had a moped puch when i was young and needed a new crank the crank had the timing for the ignition on the flywheel and it was on the wrong spot so when you push started it it would run backwards just like normal , only found out it ran backwards when you try and take off and it moved backwards but only shortly as the resistence was enough to undo the clutch-nut and clutch fallen apart and that was it no drive .

the problem with running backwards is that bolts will come undone as they are designed to tighten when the engine runs normal, it can be done. I had a moped puch when i was young and needed a new crank the crank had the timing for the ignition on the flywheel and it was on the wrong spot so when you push started it it would run backwards just like normal , only found out it ran backwards when you try and take off and it moved backwards but only shortly as the resistence was enough to undo the clutch-nut and clutch fallen apart and that was it no drive . dont know if it had enough power sounded ok and had the power to undo it self only thing was the flawheel was on the wrong spot that generates the spark lifts the contact and produces the power for ignition.

Bit big for a weedeater, but GM Diesil,s were bad for it too. blow the oil out of the aircleaner, etc.

there is no need to change the barrel etc, the ports are in exactly the right place already, the ignition will need retiming

these chinese chainsaws selling on here do it quite regularly, their timing is very close to tdc and a slow pull on the cord will get them fired in reverse, they are then running a little retarded so don't have the same power, and due to the retard they do sound different
yes I'd imagine clutches etc would need lock tabs or staking to keep them tight

The pistongoes up and down the same way uncovering the ports regardless of the way the crank is running-its just an ignition timing thing

Can you just Literally, turn the engine so it faces the other way!