Im working on a '00 sportsman 500. It will start up with starter fluid thru the intake. I have a fuel delivery issue that is either in the fuel pump or the in the carb. Im trying to understand how the diaphram fuel pump works. Behind the diaphram the fuel line coming into the pump is intermintantly sucking when the motor is turned over. I assume this moves the diaphram in and out and pumps the fuel into the carb. If that is correct what Im wanting to know is the other two lines coming from the pump to the carb, are they both supply lines or is one an overflow return line? Also, if they are both fuel supply lines then does one or the other a main supply or what? Im just trying to get the understand how its supposed to flow so I can make sure it is working properly

 

Top line to the pump is the fuel inlet from the fuel valve. Below it is the outlet to the carb. The angled nipple marked by a "P" is the vacuum line that goes to the other side of the carb.As the engine turns over it creates a suction on this line that starts the fuel moving through the fuel pump to the carb. Easy way to tell if the fuel pump is working properly is to pull the fuel line from the carb and crank the engine over. Should be a steady flow of fuel. If not could be a stopped up filter or a fuel pump problem.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

OK, I rebuilt the carb and got the fuel pump working and it will start right up. I adjusted the choke and the idle and it idles smoothly. Problem Im having is it will bog and backfire through the exhaust. I put fresh premium fuel, new E3 spark plug, it does that with and without the air filter on it. I set the pilot screw at 2 turns out. It seems like the last polaris carb I rebuilt the pilot screw had a spring and an o-ring or washer or something like that on it. This one just has a spring. Is it missing something? Also, the muffler is crappy and we have it off and have another ordered but could no muffler cause that? You have been a great help, thank you so much

 

Could be pilot screw if you're missing the spring washer and o-ring. #27-30. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse Muffler being off could cause the back firing also, BUT I'd check the valve setting along with the cam shaft for any abnormal wear on the exhaust lobe as this was a common problem on the 500 engines until the 2001 500HO.Symptoms were that they would idle,but wouldn't take throttle and back fire. http://forums.atvconnection.com/pola...d-cam-pic.html