Sand will easily take a third of your engine away from you. You need as much torque as you can create.
Gearing:
There are only two places you can adjust gearing. The drive gears in the final transmission and the sprockets. The 13/40 gear set was the best ratio that came with some buggies - SycArms may have an even better ratio for you to swap in to drop gearing. If you have an external reverse you will have 15-17t drive sprocket and you want the smallest sprocket you can fit. If your reverse is to the left of the sprocket, you will be able to use a 13t sprocket. Stock axle sprockets vary from 27-39t - The largest the sprocket that will fit without modification is usually a 39t, but some swing arm configurations allow a 42t to clear.
Engine Breathing:
Remove the restrictions in your intake and exhaust to make the engine flow better. Changing the cam to a long duration torque model A11 or A12 will help get the motor moving under load.
CVT Tuning:
You want get the engine to stay in it's peak horsepower curve by lightening the variator and stiffing the main torque spring. 12g slider weights will give the variator full range while keeping the engine in it's peak RPM. Using a red torque spring will drop the the variator to lower gearing quicker when you let off the throttle plus it will keep more tension on the drive belt. Running other clutches or variators in sand will not help you. Also changing over to heavier clutch arm springs will stress your CVT too much and result in component failures.
Tires:
The 150cc GY6 does not have much power, so paddles will hurt performance since it will have too much bite not be able to spin them. You are better off a pattern like the AMS Zipper or even a turf tread that float on top of the sand. Try to keep the rear diameter short, but the footprint wide. Our buggies are not like rails with light front ends - You want a tall and fat tire up front so it does not drag you down.
Ignition:
High powered coils and CDI's will not make much of a difference until you do the other modifications to allow the the engine to spool up more.
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