Fuel wont stay Primeed

Hey all, im looking for some input on what might be happening with my bike, My fuel line wont stay primed. i keep running out of fuel and air is getting trapped. why wont me fuel line stay filled?

New gravity fed petcock
cleaned that carbs
gas cap open
new inline filter

with the fuel line disconnected from  the tank, fuel flows great.
Klein CV34

thanks

 

Ditch the filter.  If the tank is cruddy, clean it.

If the filter is designed for a pressurized system, it will cause the symptom you describe. One indication is a paper element. If you want to run a filter, you need one designed for a gravity feed system. 
Giving an old  tank a thorough cleaning is always good advice.

This method works well unless there is a bunch of rust.
www.kwick.biz/how-to-flush-your-fuel-tank/

Do you have a problem or is it just that you are seeing “air” in the line

Nothing wrong with running an inline filter but you describe typical symptoms of the inline filter being fitted with flow direction back to front. 
If the filter body doesn't have a flow direction arrow on it then rule of thumb is the inlet end fills the outside chamber and outlet end is the inside chamber. 
If fitted in reverse you'll have chronic fuel starvation. 
 

If it is "the wrong way round" throw it away - if you turn it round all the crap that has been filtered will be washed into your carbs 

I have a problem with running out of fuel after 15 minutes or so. Fuel stops flowing

Double post. 

That's the symptom of inverted inline filter. 
The flow is restricted not shut off, so your bowl fuel level gets gradually lower as the resupply is less than the usage until there's insufficient level in the bowl to run. 
Simple visual check if you have the clear body type of inline filter. 
If it's not that then you can look elsewhere but check it first before over complicating things.
If it's not that then as its gravity fed only the air breather in the cap being partially/fully blocked creating a vacuum in the tank or crap in the tank blocking the tap could cause the issue.
Also ensure your fuel pipe has continual downward trajectory from the tap. If it's hooped above the tap level you could possibly be creating an air lock in the pipe. 

Also..because You mentioned "rebuilt" the carbs. Make sure YOU didn't plug the float chamber vent lines, just because there is a loose port/barb doesn't mean you should plug it!