80s Johnson 20 thru hub exhaust not thru hub?

[Rodman738]

I purchased a 20 hp Johnson with a bad lower unit a while back. I also got my hands on a 35 johnson that was locked up.
After switching lower units which were practically identical I got motor running. Seems to run fine other than its kind of loud! I noticed there is no exhaust coming out the lower prop hub? Seems like all exhaust is coming out upper part of exhaust housing. I've looked at a few parts diagrams but can't figure out what I'm missing or what is different! Hope someone can shed a little light on my issue I'm exhausted!!

 

[TrueNorthist]

Likely either a mismatch or the lower exhaust seal is damaged. Take the LU off and inspect the black seal just behind the waterpump housing. Measure it and the corresponding midsection exhaust channel it mates to. Back pressure is significant with the leg in the water and any splits, debris and/or excessive hardness will leak. Exhaust will follow the path of least resistance, and we all know full well resistance is futile...

Has the powerhead been off? Maybe it needs to be taken off?

 

[Rodman738]

I will take the lower unit off and take another look. Probably wouldn't hurt to take power head off and see if anything needs replaced. Thanks for advice!!