Leaderboard

It’s a 500 so right out of the gate you know 1-3/4 will be the minimum. Start there and adjust out. Keep the idle as lows as possable to keep the bike running. As you adjust the fuel/air mixture screw the bike will rev up as you get better. While this is going on you will have to lower the idle. Keep adjusting until the highest point of reving. That means at some point the engine will not continue to rev higher but start to act up. Once you hit that point you have passed the sweet spot. Back it down and make final adjustments. The highest revs mean the bike is getting the most out of fuel and air.

There is a download of the service manual in the forum's downloads section .

Check plug for spark and the carb for fuel. Seafoam won't clean out a plugged jet if that turns out to be the problem. You'd have to take the carb off and clean it thoroughly. No spark is harder to chase down. First check the electrical harness for any loose or corroded/ broken connections.If still no go you'll need a service manual to get the specs on the components , or if you have access to compatible ones to swap out one at time to find the faulty one.

Can't help on the axle info but I believe the line going to the top of the carb is the impulse line ( I misnamed it "vent" ) that makes the fuel pump work. As you found out the motor will run on gravity feed alone. More than on owner has bypassed the fuel pump and just run the fuel line directly from the fuel valve to the carb and blocked the vacuum impulse line from carb to fuel pump. There is a service manual for your quad available in the downloads section that should help you working on the front axles/ differential.