Scarab low water flow starboard side
 

I have a 85 scarab with a 5.7 vortec engine. The engine was rebuilt when I got it don't know what has been done to it. It really needs some marine upgrades on the engine carb ingition etc which I already have the new parts for.
When I got it, the starboard side exhaust was always slow on the flow the port side kicks the water our really well.
There was a new drive installed on the boat its a Merc but the lower gear case was leaking oil really bad. I took the drive off pressure tested the uppper and it passed. I took the lower resealed it and put in a new pump. I started it last night since last year and the starboard exhaust is still low on the flow when I run the motor up the water came out better but not as well as the port side. With flush attactchment on the drive.
My thinking is a cirulation pump is bad . I have a new pump I am also going to put in a new thermostat. Any other ideas? This is my first boat with thru hull. Thanks guys Roger