How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

I heard adding the right back pressure helps reduce the amount of lost fuel out the exhaust and can also add better power efficiency. Or adding a fuel control valve will help, but you have to be very aware at all times that its on the fuel line if you throttle up alot or are running wide you could burn out the motor b/c lack of oil. Tell me if im right with this or if you have any ideas that work or anything with modifications that will work on the motor.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

Those engines were never fuel efficient, they used a lot of gas compared to newer models. The fuel flow is controlled by the needle/seat in the carb, it flows fuel as it is needed, an external control valve is not going to help.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

kyle45133 said:

I heard adding the right back pressure helps reduce the amount of lost fuel out the exhaust and can also add better power efficiency. Or adding a fuel control valve will help, but you have to be very aware at all times that its on the fuel line if you throttle up alot or are running wide you could burn out the motor b/c lack of oil. Tell me if im right with this or if you have any ideas that work or anything with modifications that will work on the motor.

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I don't know how you plan to "add the RIGHT confused back pressure".

But as far as restricting fuel flow to the engine, that sounds like a quick way to burn holes in the pistons. The engineers calibrated (theoretically) the carburetors to supply the correct amount of fuel needed to allow the engine to not only make power, but also keep the engine from leaning out, or going too rich. It's a delicate balance. Throwing some sort of valve in the fuel line in some half-azzed attempt to get better fuel consumption isn't going to turn out well. It's not a toilet or shower that you are trying to restrict down to save money on your water bill. It's a piece of machinery that depends on the correct mixture of fuel and air to keep chugging.

She's 50 years old, don't abuse her for the sake of saving a buck. If you want something that's more thrifty on fuel, get something at least 2-3 decades newer, or something smaller.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

There is nothing you can do to make that engine more fuel efficient. It is what it is either live with it or buy a newer engine. That motor was built when gas was cheap and no one was concerned about pollution.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

a) cut and plug gas line.
b) get a set of oars
c) use the oars exclusively
d) done

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

Pray that it turns into a late 70's three cylinder 75 HP, you will be a lot happier.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

thats a good one. Ill go with a) for 200

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

194269 said:

Pray that it turns into a late 70's three cylinder 75 HP, you will be a lot happier.

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What year does the 3 cylinder 75hp start?

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.



this is what i mean by back pressure.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

http://2strokeengine.net/2strokeenginetuning/2strokeengineanimation.php

image wont come up so here is the web site to understand back pressure.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

kyle45133 said:

http://2strokeengine.net/2strokeenginetuning/2strokeengineanimation.php

image wont come up so here is the web site to understand back pressure.

Click to expand...

Yeah, I understand 2 strokes, and back pressure. Problem is you have an outboard motor, not a 2 stroke motorcycle, or snowmobile, which actually uses a tuned pipe like what was shown in the article.

All your motors exhaust exits out of the lower unit. Back in the day, there were some outboards that were equipped with funky pipes coming out of the engine cover. Those outboards were used for racing. And I'm sure little regard was given to fuel consumption, noise, and longevity from those outboards too.

And not for nothing...building tuned pipes isn't as simple as making a trip to autozone for different sized exhaust pieces. There is a science to it that requires more skill and figuring than just reading and copying an Internet article.

Leave your vintage outboard alone. Either keep it in good repair, and enjoy it for what it is, or sell it for something newer.

A sweet old OMC "survivor" doesn't deserve to be hacked up or experimented with like a science project.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

I've decided to leave it be and rebuild it to its former glory. It will look good on the back of my steury boat. Here's the kicker the outboard that came on my boat was actually an amc 25 hp. I'm going to rebuild it to use for cruising and just having a relaxing time, then use the johnson 75hp for fast fun.

thanks for the answers and comments.

Re: How to make my 1961 75 Hp Johnon Seahorse more fuel efficient.

I think you made the proper decision.