The snorkel kits restrict air flow to the engine and reduces power by around 10%. I would expect something on the order of a 5-7 mph speed decrease, but it is well worth it if you need the snorkel.
Gasoline loses its octane and combustibility significantly after just a few weeks.
I would put in fresh gasoline and try it for power. If it is just down slightly with fresh gas, then it is just the impact of the snorkel.
If you leave the ATV parked for more than a few days at a time, add just a very small amount of Echo, Sthil, or Husqvarna chain saw oil to your gasoline. It will keep the fuel fresh and will stop fuel system corrosion. I buy my fuel in bulk and treat my entire gasoline supply at the rate of 1/8th the amount that is called for for on the chain saw oil bottle, and have zero fuel related problems and performance is unaffected. Do not use the cheap generic or box store oils, they suck and do not have the preservatives that are required.
A forum community dedicated to Kawasaki Motorcycle owners and enthusiasts. Come join the discussion about performance, modifications, troubleshooting, maintenance, off-road, touring, street bikes, and more!