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Blown head gasket usually will not kick back fuel into the air box like that. It's usually contained to the cylinder head and very easy to hear. BUT a compression test definitely could not hurt!

check spark and compression as well. could be a blown head gasket

Hey @Steven Urban welcome to Quadcrazy. The second part you show in the picture is your starter circuit relay. It all starts from your neutral safety switch. It looks like its in bad shape but they still work in that condition. Anyway you should have 4 wires going into it. Light green, brown and two black ones. Here's how it works: the green wire runs down to the neutral safety switch on the left side of the engine right above the shifter. The brown wire is a 12v positive wire. The two black wires are what completes the start circuit when touched together. Here is where to start: take a jumper wire and jump the two black wires on the relay together and hit the start button. (Make sure the atv is in neutral) and see if it cranks. if so thats good. After that; Take a tester and see if you have 12v+ on the brown wire at the relay. If so then thats good. Now the green wire is simply a ground thats made when the atv is in neutral. That green wire has a device inside the engine that when clicked into neutral it grounds the green wire. So in essence the 12v brown on the relay and the green (ground) when put in neutral energizes the relay and brings the two black wires together and also brings on the neutral light. If you have no ground from the green wire then put a jumper from green wire on the realy to a good ground. If that works then the neutral safety switch is bad. That starter circuit relay is an easy find if need be. Do some of these test first and lets see what you get. https://www.ebay.com/itm/153882535043

Hey @Amboyjim welcome to Quadcrazy! Check the diaphragm on the fuel pump. If the diaphragm is bad and gets a hole in it the fuel gets sucked into the carburetor via the vacuum line and floods the engine and winds up getting kicked back into the air box. Also when you set the air fuel screw after the carburetor rebuild did you set it properly?

dang right👍