Hi guys,

Probably a really stupid question but I was hoping someone could clear it up for me. I'm told the MC21/28 carbs have slightly different sized jets standard. Why is this? Exhaust differences? Engine geometry? The difference in the heads between front and rear cylinder? If you run a head from the rear cylinder on the front do you end up running the same jets in each carburettor?

Thanks
Jim

Only the Mk1 MC18 has staggered jetting as standard, but all NSR250s have staggered needles, making one cylinder effectively richer than the other.

The difference is one cylinder is more efficient than the other, and as such, each cylinder should be treated individually. Think of it more as two 125s that share a common gearbox.

Inlet path and combustion chamber design are the main contributing factors. As far as I am aware, the exhaust lengths are the same on each model, but a more convoluted path for one chamber may be another "restriction" that effects jetting too.
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Andy.
NSR-WORLD.COM

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