Check your float heights. My MC18 used to run dry just before the braking zone at Ruapuna and just after the entry road at Teretonga, cos I had the float heights wrong (like that when I got it).

you're wide open for less time in 1st/2nd than the other gears, less time to suck the carb bowl dry.

Check your splice. If its spliced to first or second gear, the ignition advance is more than the other gears.

And finally, look over all your carb gaskets etc, make sure that you aren't sucking air in somewhere else. My little brothers IT200 siezed or holed pistons about 6 times before we finally fixed the problem (twice with me on it ) too much compression leading to the base gasket blowing out, leading to air being sucked in leading to . Solution: thick, wire reinforced industrial gasket material. Made it gutless, but reliable...
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The Chopster