[440Tim]

If you have to use the choke to keep it running it's probably lean. Either air leaking in somwere or it's not getting enough fuel.

Your Chinese knockoff carburetor may not be jetted right for your quad. Or the mixture screw may need turned out farther.

Could also be a vacuum leak. I'd start the engine. Then spray some carb clean or starting fluid on the intake between the carb and engine. And on all the vacuum lines. If it has a leak you will hear the idle go up or down depending on what you spray it with.

Could also be an issue with the fuel petcock or fuel pump. It also could be a clogged fuel filter or in tank fuel strainer.

The vacuum leak is probably easiest to check for so I'd start there.

 

[440Tim]

Some fuel petcocks do not have the vacuum port. If yours was replaced with this style you should be able to cap it's vacuum port on the carburetor. Any local auto parts store should carry vacuum caps to plug the port.

The vent on the fuel tank cap doesn't go to the carburetor. It's just a vent. Usually would have a line running from the cap down through the plastic panel around the shifters below the speedometer. If you zoom in on this pic of mine you can see the vent line coming off the gas cap.