Quote:
Originally Posted by Rusty Heap
Here's a Piston comparison, Banshee ATV 2 stroke twin, 350cc stock.
A Big Bore 404cc stroker engine piston on the left, Stock on right, but joined with a common wrist pin.
Big bore dyno'd out at about 60 hp.
Illustrates how on a 2 stroke, the pistons' fuel window port timing can be shifted to make mo' horsepower. As well as piston skirt height.
Note also, Left big bore piston exhibits the classic 4 points seize from a too lean on-top at max RPM's. 
Too hot piston skirt expands / swells up then seizes the engine locked up tight...........yeah unfortunately at ~60 mph on pavement, so pull in the clutch, coast to the road side.
Let engine cool for 5 minutes, kick it over and ride it home.
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Increasing bore on a 2 stroke also increases compression ratio unless the dome is relieved. That means it needs to run richer.
Radical porting mods also mean it needs to be richer.
Some folks like to "break-in" with extra oil, which makes it run leaner.
Hopping up a 2 stroke for more power almost requires needle and jet moves to richen, otherwise hot sieze.
BTDT lesson learned the hard way in my yoot.
