1986 Mercury 75 hp 4 cyl vs 1991 Mercury 75 hp 3 cyl

[mgsolakis]

1986 Mercury 75 hp 4 cyl vs 1991 Mercury 75 hp 3 cyl. Which one is better? I assume the newer 3 cyl would be better on gas. Would the 4 cyl idle better? Do either of them troll well? The 3 cyl is oil injected is that a good thing? Which is faster?

 

[James R]

Re: 1986 Mercury 75 hp 4 cyl vs 1991 Mercury 75 hp 3 cyl

Most two strokes hate idling. It doesn't make a lot of difference 4 cyl or 3 cyl. When Mercury got their act together and realized that an oil tank up at the motor works and an oil tank on the deck causes problems, their oiling system got up to where Suzuki and Yamaha have been for years. A good oiling system with little trouble but the oil pipes to and from the pump have a habit of brittalizing and splitting. These should be checked every season and replaced as needed.
I run a 60HP Big Foot on my toon and have noticed this failure on mine and other similar Mercurys that came to me for service. Another failure that is common is the oil level switch float, if that is what is in there. The switch itself rarely fails. I suppose that is why they put the window in the cover. If it does fail you can disconnect it to stop the beeping. To fix it the whole tank has to be replaced.
Speed is a function of engine, prop and load.

 

[pckeen]

Re: 1986 Mercury 75 hp 4 cyl vs 1991 Mercury 75 hp 3 cyl

Both motors should have the same power. Which one to buy? I prefer oil injected over having to mix the oil myself. Having said this, is the price is the same, the one to buy is whichever one is in the best condition.

 

[jimmbo]

Re: 1986 Mercury 75 hp 4 cyl vs 1991 Mercury 75 hp 3 cyl

A 3 cylinder will get better fuel economy than a 4 cylinder of the same power being than it is easier to tune the exhaust over a greater RPM range than with a 4. The 3 is loop charged, which will help fuel economy, while the 4 is direct charged which is a variation of cross charging, which usually makes for smoother low speed running. Since both are rated 75hp the top speed should be about the same unless there were improvements in gearcase design.