the induction cycle is symmetrical around TDC, a major drawback of piston ported engines.
as stock standard, it is 120 degrees, from memory. the 1/4 inch notch brings it to around 150 degrees. ie, as piston goes UP 75 degrees drawing air IN, it also DESCENDS 75 degrees, expelling some of that fuel air mix back out the carby...
so doing BOTH 1/4 inch notches results in possibly over 180 degrees. great ONCE the engine is doing hi rpm, and the sheer momentum/inertia of the air prevents it from "reverting" back up the inlet manifold... bad when the engines running slow.
this is what reed valves are for
assymetry of induction stroke means good power through the range... ie, the piston sucks IN on the upstroke, but the reed valves CLOSE, compress the mix all the way from TDC till the transfer ports open.
the EXport mod you made, towards the TOP of the cylinder...increases open time. so what was 140 may now be 150. the shortened time for the power stroke(increase port open, decrease power stroke...) is where your low end torque has gone. (and 70% exhaust port would be over 2/3 of the piston... maybe big on some, but never that big. still need space for the transfer ports, etc.)
yes, maybe WIDEN the ex port, careful not to exceed the end of the rings or it shall be messy. but really? its big enough. 250ish square mm.
the transfer ports also need to be increased to some point to match...
without a custom designed pipe, the portwork is virtually pointless. it will be a marginal gain in these things.
also, you dont get both low end and top end from twostrokes. dammit! either always less, over more rpm... or more...at one lil revband...
a nice pipe on these engines do make all the difference from being a lawnmower engine to something slightly more interesting, btw
you wont believe its the same engine.
you have a fine line between piston induction, exhaust timing, and intake/transfer timing. one degree too far one way... oops!
i suggest a new cylinder, left alone, with a pipe. you will die of shock