water flows through tell tail only when exhaust pressure drops.

I have a 4hp yamaha 2 stroke outboard. There is a rubber "bung" for lack of a better word on the side of the shaft about 1.5" in diameter which you remove to get to the shifting linkage. when removed the exhaust flows out through that hole and instead of through the prop dropping the pressure inside of the shaft and water starts to flow through the tell tail. When the bung is in place there is only steam and exhaust flowing through the tell tail. I'm pretty familiar with cars and motorcycles but haven't played with outboards much, I know 2 strokes need a certain amount of back pressure on the exhaust and i may be throwing that out of spec when i remove the bung, and can i remove that bung and just let the salt water flow into there? I know its probably an odd question but I appreciate any help on the subject.
And the impeller only has three of six fins, but i did find all three of the other fins from the impeller and remove them.

post a picture

what part of the outboard would you like a pic of?

the plug you r taking out

This isn't my motor but it is pretty much the same, the plug when removed gives you access to the shift rod where you can disconect it when dropping the lower unit to work on something like the water pump.

so removed it pees?

correct, and when in place exhaust comes out the tell tail, should exhaust even be able to get into the cooling system? and seeing as the impeller for the water pump has only 3 out of 6 fins, will replacing it fix the problem by giving the water pump the extra pressure to overcome the exhaust gas and pee? or can i run it with the plug out and it will work fine? or will that not provide the right amount of back pressure for the engine exhaust and let salt water into places it is not supposed to be?

2 stroke yes

i would take the lower unit off
and replace t-stat and back flush

no thermo stat on such a small motor, its just a 2 stroke 4hp.

get me the full model number

Check if there is an oil-seal in the impellerhousing where the driveshaft enters the housing. This stops exhaust getting into the waterpump.Replace this seal and obviously your impeller and it should pump water fine.