I want to convert my 1977 Evinrude 115hp to a 140 hp. Can i…

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Answer 1

Answered in 18 minutes by:

10/12/2011

Marine Mechanic: Jason, Marine Mechanic replied 11 years ago

Jason, Marine Mechanic

Category: Boat

Satisfied Customers: 25,430

Experience: Degree in Marine Technology. Gas and diesel marine mechanic.

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My name is XXXXX XXXXX I will be helping you today. Most questions will involve troubleshooting, and usually take many posts back and forth.

What your looking at is different carbs and a different exhaut tuner, and sending out the block to have the ports machined. A whole bunch of work. If doing this yourself your looking at 15to 20 straight labor hours. Plus whatever you have to pay the machinist for his time.

And this does not include spending time to procure the parts you need.

The question is... where are you going to get the parts from? They don't sell carbs and exhaust tuners any more, not new. Anything you will find is going to be over 30 years old, and hit or miss.

The differences between the 115 and the 140 are going to be carbs, exhaust tuner, and port location on the block.

All of these items are a somewhat doable if your talking about a 6 or 7 year old Mercury. But on a 34 year old Evinrude.... there is just no place to get the parts you need. On top of that, lets be realistic. Not including your own time, what your time is worth to you. If you can find the carbs, if you can find the exhuast tuner, after you pay for the machine work. Your looking at at least 1500 to 2K in parts an machining cost before you put your own time into it.

I look at motors every day, and i'm going to look at one tomorrow that I will more than likely pick up if it checks out good. What i'm looking at is a 2003 Mercury 150 V6 EFI fuel injected engine for 2700 or best offer. If it checks out i'll get it for 22 to 2300. Converting your 34 year old evinrude just to pick up 25 is going to cost you at least that much by the time the job is all said and done.

But to answer your question speficially. And I do repeat myself a bit here. You need carbs, exhaust tuner, and a whole bunch of machine work. Its not a cost effective upgrade.

Post back with any follow up questions

Good luck!

Jason

Answer 2

Marine Mechanic: Jason, Marine Mechanic replied 11 years ago

You still need to get the exhaust tuner out of the old one and get it into the new one. Which means striping down both motors to their bolts. But that's 1/2 the battle.

2 stroke engines do not have valves, they have ports. Port height, width, and location all play a part in overall HP. You have to take apart your existing engine down to the bare cylinder block and send it out for all the machine work necessary. Aside from breaking down the block, chances are you won't find a machine shop in your area that has all of the specifications , and can do the work reliably.

If you simply bolted on new carbs, and changed out that exhaust tuner without changing the ports. It's going to run worse, with less HP, and not better. It is an all or nothing deal.

As you can probably tell i'm trying to talk you out of it. I have been down this road many many times. And I am trying to save you money and headache here. For something that old it is just not worth it. You would be much better off selling what you have and buying what you want versus going through that much trouble. Even with the later model stuff, where parts are plenty available, it is still to much work to justify it.

I don't want you to accept my answer and leave me bad feed back. If you want a 2nd opinion you are entitled to it. But if another expert tells you the same thing.. I hope you will think of me when choosing which answer to accept. But thats up to you. If you had a mid 2000 engine, my answer would be completely different, and more worth while. But for a 34 year old engine.... Outboards are not like car engines, like your chevy 350's.... Once they get so old thats it.... there is no bringing them back, no parts available, to expensive ect. Do some research on your own. But for the most part outboards are "throw away" engines".... The manufactorers of them simply do not support them after they get so old.

Answer 3

Marine Mechanic: Jason, Marine Mechanic replied 11 years ago

Keep in mind is that Boats.net is not an Evinrude dealer, simply a re-seller. So take what they say for a grain of salt until you talk to a true evinrude dealer in person.

What do you mean by "What would you do if 1 out of three answers were incorrect, would that build confidence and trust in the other 2 answers?"

Answer 4

Marine Mechanic: Jeff G., Marine Mechanic replied 11 years ago

Jeff G., Marine Mechanic

Category: Boat

Satisfied Customers: 4,730

Experience: 42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance

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Welcome,this question may need more than a single answer. Please post back with additional questions on this at any time.
The 115 and 140 carbs are a different size, as well as jets.
A 140 powerhead will bolt right up to a 115 midsection.
The exhaust back on the two engines is different as well. Your 115 uses a flat back exhaust. The 140 uses a bubble-back exhaust. To convert a 115 block in addition to porting you would need to have the block machined to accept special exhaust stuffing blocks and the bubble-back exhaust.
In the midsection the 115 was restricted where the 140 had a more open tuned exhaust. So unless you also changed the tuner under the adapter plate you would be choking the 140.
Basically much of what Jason posted was correct.
Other than the exhaust chest, tuner, engine block and carbs the other parts will interchange.

I want to convert my 1977 Evinrude 115hp to a 140 hp. Can i…

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