Since I am asking question today I have another one. We have a small boat 15' with a 1988 2 stroke 75 HP Mercury outboard. The engine is so load that the wives often don't want to go boating because of the noise. Is there anyway to dampen the noise to a more acceptable level. I was in a friends 70HP Mercury of about the same vintage and it was night and day, his was relatively quite while mine was extremely loud. Any ideas what might be going on or how to dampen the sound. Claude
Is there any noise insulation under the cowl cover? My 1983 25 HP Mercury was very loud and underneath the cowl was bare. I got 3-4 sq. ft. of 1/2" foam padding at an Arts & Crafts store and with contact cement applied it underneath the cowl. [Don't ever let any of this get into the carb intake.]Incidentally, my older 9.8 Merc had factory insulation under the cowl, which was a good noise suppressor. Maybe my 25 HP had it with the previous owner and it was discarded along the way.
Here is another possibility but a long shot. The exhaust tube that connects the exhaust plate in the powerhead to the lower unit may be missing. My 40hp had the same problem with noise and when I removed the lower unit to change the impeller I discovered the exhaust tube was gone. A previous owner had removed it for some reason. Installed a new one and it made a HUGE difference in noise levels. When I start this motor now it is hard to tell when it kicks over it is so quiet.
pour some 2 cycle oil in cylinders and start motor.it will smoke alot and might show any exhaust leaks.i found a small hole in the block on my johnson by doing this.the motor sounded like a harley davidson until i found and repaired the hole.
In my experience, the cowling insulation makes a little difference, but not a huge difference. It certainly won't hurt, but I wouldn't guess it would make a night and day difference - which is what it sounds like you're looking for. The great majority of the sound comes out the exhaust and a relatively smaller amount from the powerhead. I'm interested in the theory that the exhaust tube's disconnected or gone.
DoctorCad, it's been a few years but I rode those bad boys as well.." Whats wrong with that" you ask,it would scare the heck out of the fish ! LOLImagine a v twin stroker with straight pipes mounted to a skiff coming down the canal..LOL
I never had a 75 but I did have a 40 1978 2 cycle and it was louder than my newer 40 but not appreciably so. A 75hp should have a high whine and at full throttle is probobly the same. Is the motor exhaust covered when the wives are in the boat, meaning do you have trim and tilt or do you need to trim the boat manually with the extra weight(not saying your brides are not lighter than the air) with the adjustment bar?