Merc 650 65 horse.

[Erie Steelman]

I just bought a boat with a Merc 650 65 horse outboard. I am not sure if it is a 2 cycle or 4 cycle engine. The serial number is 3403892 and I think its a 72. Previous owner stated that it takes straight gas but I am not convinced he's correct. He started the engine for me before I purchased it and it seemed to run well. I'm concerned that he may have been operating the motor without gas/oil mix for some time. If so what damage could he have caused?

The merc is on a 72 Caravelle which has a merc control throttle and steerng wheel. I dont want to run it until I the fuel mixture. Or maybe the previous owner is right and I dont need a mix???

As you can see I am new to this, but am willing to learn since I love fishing and getting out on the lake. I looke all over the boat and cant seem the find the info anywhere. Thank you for your help.

 

[Grizzlybear]

Re: Merc 650 65 horse.

Google it. Its a four stroke or a two stroke. Four stroke (to my knowledge) requires straight fuel, 2 stroke definitely needs oil/fuel mix. If it were a two stroke and the fella has been running it on straight gas he wouldn't have had much of a motor to sell.

I could not say for sure, but it sounds like a four stroke. As I say running a 2 stroke without adding oil to the fuel would end fairly catastrophically, fairly quickly.

But. Check it out defo, as if it is 2-stroke, you gotta be adding oil (as far as I know)

 

[Grizzlybear]

Re: Merc 650 65 horse.

Is this it?

 

[Erie Steelman]

Re: Merc 650 65 horse.

Yes that looks exactly like it.

 

[Erie Steelman]

Re: Merc 650 65 horse.

I look at it again to make sure. On the back, it actually has a silver face plate that comes off before the housing with the two halves come apart.

 

[Erie Steelman]

Re: Merc 650 65 horse.

I googled the motor and did some research, and called a couple merc dealers. Every source is leading me to believe that this motor is a 2 stroke. However, the orginal owner keeps saying that he has only put straight gas in and never had a problem. I bled the gas tank and found the color of the gas in the tank to be green, which I assume would indicate some oil in the tank.

Question: Does this motor somehow mix the oil in automatically, or did I just buy a potentially bad motor since he said he always put in straight gas. Sorry guys, I'm a novice at all this. I dont want to mix 50:1 if it is not needed, but i dont want to fry the motor either.

P.S. The guy I purchased it from fired the motor up before I purchased it. It only took him a couple tries and the motor seemed to be running fine. Thanks for your help.

Erie Steelman is really confused

 

[Aqualift]

Re: Merc 650 65 horse.

It's a 72 two-stroke triple. You premix the gas and oil in the fuel tank. 50:1

End of story.

If you detect oil mixed with the gas, I wouldn't worry about it. If it makes you feel better, get the compression checked on all three cylinders. If it was run on straight gas for any length of time, there would be some serious issues.
Bearings would have also taken a beating.

 

[Erie Steelman]

Re: Merc 650 65 horse.

Thank you. I will try to put it out first and go from there. I appreciate the advice.

 

[Moody Blue]

Re: Merc 650 65 horse.

Erie, if the owner was being straight with you he may have been mistaken on what he was buying. Some marinas sell premixed gas from the pump so when he was buying "straight gas", it may have in fact been premixed already.

No way the motor would last more than a few minutes running on straight gas. It would overheat and seize within a short time.

There is no oil injection on that motor, so do as Aqualift suggested and premix at 50:1.