We are running 19/36 in my Dad's '90 Indy 500. Plenty of chain if it is stock length. Below is the set-up used in that sled for fast trail use.
Polaris gold primary spring 100/275. For higher engagement, EPI white 120/280 (adds approx. 200 rpm to engagement) or black 145/280 (adds approx. 400 rpms to engagement).
Polaris #10 bushed weights
42/34 full progressive helix
HSP white secondary spring #2 position
19/36 gears (much quicker)
The clutching and gearing changes made it a great sled on the trails for a sled with 72 HP. Also went 1 size smaller on the main jets and 1 notch leaner on the needles. Still safely jetted for most riding.
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