On the compression stroke, what stops the charge going back through the bypass port and then in to the carburettor / venturi picking up a second charge.
Hmm of course conventionally a valve will stop back flow in a 4 stroke and the piston skirt or reed stops it in a 2 stroke, in this case the back flow isn’t stopped by either lol. Will call you laterwell yes, that happens on all engines, I called it pulse.
they have a circuit for want of a better word that enables mix to go over the valve assy, cam and crank and lube like a normal 2 stroke.
Looking at the vid, I would imagine that the crank helps move the mix thru, and it is then drawn into the combustion chamber.
I would think there would be a reed petal valve of some sort to prevent backflow??? I tried looking for a good pic or diagram to show such a thing but came up empty handed. I did find a YouTube video showing some top views and I saw nothing of the sorts over/near the port.
Full disclosure, I have never worked on a 4 mix or even ran 1!!!
the kubota 130cc engines i do for the bowling green mowers have a very crude decompressor that jabs the inlet valve open a tad just before tdc, and they suffer blowback, with fuel being sucked up the mainjet twice, and if the valve clearance is too tight it dumps too much compression, and that soaks the air filter and makes the engine very laggy i have to grind some off the cam followers when they get too badThanks Frank, that’s very true, it must be because you’d limit lubrication / movement of oil mix if it was valved. I’d be curious to run one without the AF and see how much spitback does occur. Edit : clearly not enough to matter, but it answers my question!
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