> Born to be WillD Wrote:
> I mean it's not crazy, but i'd warn against taking and applying advice
> directly from a 2 stroke guru if they're not a moped guru.
> Specifically dirt bike guys, alot of the same stuff definitely applies,
> but alot doesnt, one of the big ones being the lack of gears, which can
> change alot about where you're running and where/how wide you wanna make
> power. at least you're variated though, so as long as you know what
> youre doing there you can take advantage of peakier high RPM power with
> a loss at low RPM.
> for example, you look at an RM 80 and theyre running 28mm carbs, some of
> the competition folks run up to 32 and over. That's like racing dirtbike
> shit tho, those things make at least twice the power your kit does. and
> theyre spinning up to 14k, not to mention being slightly bigger too
> the other thing to consider about carbs, and its obvious but also easy
> to overlook is that youre reading a diameter but the flow's gonna be
> proportional to the xsectional area, essentiall it scales with r^2. so
> like from a 18 to a 28 is 1.5x diameter but effectively 2.5x the size...
> that also affects your velocity. you've got a flow rate based on your
> engine's volume (draw per revolution) and RPM. so for the same RPM you
> have to have the same flow and so your velocity's necessarily gotta be
> smaller which can hurt the mixing of the charge and response. Flat slide
> might be better here also.
> or the tl:dr w less theory, similar sized high performing engines can
> use that size range of carbs, but you might be overcarbed for the
> limitations of the cylinder and engine, and see worse performance in
> terms of responsiveness and low end torque.
> and of course much worse gas mileage.
Amen to that. Velocity is important and with gears you can get that by keeping it in the red. You're going to need a fat needle to compensate at low rpm.