TOPIC: Fuel bowl level

I run twin 35 Johnsons, have a 15 gal fuel tank under the front deck. Each has it's own pick up, anti siphon valve and filter primer. I am a little perplexed as to why the port bowl stays full all the time, but the starboard bowl level will drop, as seen in the picture. (it will fill by priming) It will run all day like that, never runs out of fuel. I thought if there was a restriction in line, or faulty anti siphon valve it would run out, if the fuel pump was weak, the bowl would stay full. Scratching my head, any thoughts?
Thanks
Cheers
Bill

That's the second time I've gone to the JEGO section to post and it turns up in the main forum.
What gives?
Cheers Bill