Polaris 300 Xpress prime to start

It is a 2 cycle. If i have not run it for a couple of days i have to prime it. Carb has been rebuilt, new fuel lines from switch to carb, filter is fairly new, and fuel tank switch replaced last year. I am thinking lines from tank to switch, filter, or maybe a defective switch valve. To me it seems to have an air lock preventing fuel from filling the bowl. Once i prime it runs great and will start after shutting down with no problems.

Unless it is a electronic fuel injection, that is pretty normal procedure. I had an older Yamaha Grizzly that in cold weather you had to have the machine in full choke for the first 50-100 yds before it would run with being choked. It was a 4 stroke.

Does it have an electric fuel pump or a pulse pump?
If it has a pulse pump, the motor has to turn over a few times to pump any fuel - it works on alternating pressure/vacuum in the crankcase as motor spins.

Not an electric pump. I checked fuel flow out of tank after filter and fine. I put a new filter on it anyway. Primed it cranked right up and idled for 10 minutes. Took it out for a spin and ran fine. I left gas on and 2 hours later ut cranked right up. Problem occurs when i leave fuel valve off. I am going to leave fuel valve on and crank daily.

I have left the gas valve on for a week. Fires right up NP every day. Not sure why i have to prime when i turn it off. I would add a primer bulb if i had room for one.

Unless it’s leaking or flooding over leave the valve on. I never shut mine off Just my 2 cents

What do you mean when you say prime? Id doesn't have a primer button and it doesn't have a bulb, how are you priming it?

When your shut the fuel off when you store it are you turning the valve off and letting it run out of fuel and die? Could be the fuel is evaporating out of the carb when you turn the shut off and the tank doesnt keep it full.

I dump a little fuel straight in to the air filter box. I am going to do what Black Duck Dog. I was not running it dry. I did that with first Mercury i owned until i got smart and figured out it was not necessary.i think it is better for needles to stay wet.

Sounds like the tank may not be vented properly.

Im not sure on my thoughts on that. Had a 3 cylinder/3 carb evinrude on our first boat from 1985-2014. We ran the gas out of it every time that boat came off the water. The carbs were never opened and it would still fire on the first crank when we sold it.

Recently acquired a riding mower and got my old generator running after sitting for some time, the needle on either of them wouldnt seal and they would flood till i rebuilt/replaced the carbs. Perhaps the 2-stroke pre mix in the evinrude saved it over its almost 3 decades.

I discovered my four wheeler has two filters inside the tank when you drop the fuel valve. They were restricting the fuel until there was a suction on them from the engine running.

I will look in my tank but i dont think there any filters in there. I disconnected the fuel line below filter and flow looks good. I am just going to leave the valve open.

leaving the valve open should be fine as long as the float isn't stuck allowing fuel to run out. I've owned dozens of off road motorcycles over the last 50 years and that always worked fine ... I had one XR600 that the float was notorious for sticking open that I had to turn off the fuel, but leave it sitting a few weeks and it was a bear to start as the gas in the carb dried up clogging the jets.

Vent is fine I just pulled the line out of the steering column and blew through it with gas cap off. I think it is a vacuum issue. I am going to replace the vacuum line that runs from the engine to the carb.

I may have figured it out. Sometimes it pays to read the manual. I have always depressed the throttle when starting. I was looking up the instructions to clean the spark arrestor and read the starting instructions. They stated to not depress the throttle lever when starting. Tried and seems to work. I am thinking with limited air the carb sends a richer mixture.