ok i have a question for the merc guru's... im looking for some more power... looking to pick up a 140 powerhead for my next build..i have a guy who has a few laying around.. and need to know what to look for to id a 1980 140hp from a 90 or 115... i know they look the same to most,, but there has to be a sure way to id the difference.. i dont want to pick up something i dont want..
A 1980-81 140hp will have a serial # range starting with 5625108.
One way you might tell is if you pull a main jet plug on one of the carbs, with a strong light you should be able to make out the jet size of .080". A 115 or 90hp is gonna have a smaller jet.
Can't recall if the casting #'s on the block mean much of anything.
Another sure way is (if you can) pull an intake port cover. Run a piston up to the top of the cylinder and you should be able to see the round hole for the extra port in the piston (and there's extra porting in the block that you can't see). Only the 140 in this year range would be piston-ported.
Note that later in the 80's, Merc went to a prop-rating for their engines to match industry standards. So, what was a 140 became a 115. And the 115 became a 90hp.
If you find one of the 115hp piston-ported models, they are very strong runners. Just about as good as the earlier 140's.
115's starting with serial number 6436123 have the ported pistons.