What you want to try is get a piece of 3/8 inch clear vinyl hose and insert closest to engine and watch fuel flow, it should be solid with zero bubbles.
temporary use only. There are many places air can leak in.
One of the primers was leaking air in and making bubbles, all kind of problems with Johnson 200s, I even changed a fuel pump on motor and it didn't fix it. Green corrosion at one of the brass flare fittings and no smell of gas or a drop leaked.
If concerned with fuel quality, use a separate portable tank with fresh gas in same hose, bypassing boat's fuel system.
I got rid of both primers, squeeze bulbs work fine, just have to walk to stern, no big deal.
If you get bubbles, just have to work backwards to find the source in the chain.