model #906X90C exhaust leak

[graybird78]

my 90hp us marine,has bad exhaust leak when in water. the smoke seems to be coming from underneath the carbs around the shifter rod. took it to boat mechanic to have looked at. found that there was some horse shoe looking exhaust seal in lower unit that was missing. but he doesnt think that the missing seal is the culprit. says doesnt see how that smoke can get up to the motor. parts diagrams call it exhaust seal. could some explain this.

 

[jerryjerry05]

More than likely the plate the block sets on is leaking exhaust up into the motor.
Get a can of WD or something that will make smoke when burned.
Get motor warm, remove the cowl, raise the idle, spray into the carbs and inspect the base for leaks.
That not showing a leak??

Then the end of the exhaust tube inside the mid section the gasket 2 1/2"X 3" X 1/4" is bad.
You'll need to pull the powerhead to replace this.

What you can do is stuff a strip of weather stripping 1"X 1" X 2' shove this down in the area below the powerhead.

 

[graybird78]

will try that when i get my boat back.

 

[graybird78]

well i got my boat back. there was actually a gasket missing in the lower unit. i had a spare jung lower unit took the gasket from. he did say that after the repair,he ran the motor in tank for 20 minutes with no signs of exhuast leak. will take to lake weather permitting to confirm if fixed. he did say he replaced the bellows in the mid leg that goes bad becacuase it wasnt sealing very good. he also replaced the water pump at my request.