1978 johnson 115

[fiberglassiccollector]

it has 125 compression runs ok but i know it wont be fast enough and im not ditching the motor its on a 1974 glastron cv 16 im going to put a bobs mid section exhaust on it and im not sure but i think 140 heads the bubble back exhaust plate and 1 9/16 carbs are about it on these if im wrong or forgeting something please tell me just wanna max this thing out dont want a different motor

 

[fiberglassiccollector]

srry meant to put 1977 it has no power trim thought it was older

 

[interalian]

Hard to read your post without periods or capitalization, but I'm assuming you want more power from the 115?

 

[fiberglassiccollector]

That is what i am trying to do read the vin today its a 1978 johnson 115

 

[interalian]

Bigger carbs from a 140 plus the bubble exhaust may bring you up slightly. Block porting may also be different between the 115 and 140, so you won't see full benefit. Intake ports on the 140 are YUGE!

 

[jimmbo]

The 115 and 140 share the same port timing and in most cases the same size carbs 1 5/16"(jetting will vary slightly), in 78 and 79 the 140 had 1 3/8" carbs. Adding the bubble back will require some machining of the block. Also needed will be the Exhaust tuner(megaphone), the one from a 1977 140 is the best. There were several cylinder heads used on the 140 over the years, but the ones from the 1973 135hp had the highest compression. Every year after, the compression dropped slightly. About 19 1/2 years ago, Bass and Walleye Boats Magazine had real good Article about what the same and what the differences were between the crank rated 90, 115, and 140 hp, and how to make the 90 into a 115 or 140, and how to make the 115 into a 140