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    Yamaha 2 stroke

    70 horse 2003 Yamaha with very low hours. Previous owner told me to put oil in the gas tank and never trust the auto-mixing pumps. Kind of thinking he didn’t ever run this boat and don’t see why I should not just fill the oil tank.
    I looked today and it has a small amount in there. I thought it would have been empty based on what he said so I added oil to my first tank of gas which is almost gone. The motor runs ok but idle is a little rough and it doesn’t like to idle for more than a minute or two without stopping. No issue restarting on first turn. Wondering if I’m oil rich now cause there was oil in the oil tank being mixed with my already 50:1 gas tank?


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    #2
    Replace your spark plugs and see what they look like! I have a 40hp 2002 model that still runs like a top.


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      #3
      there has been many a boat motor burned up because the oil mixing pump thing did not work right. why fuss about the guy just wanting to reduce his risk by premixing his oil in the gas tank so as not to worry if the mixer system worked correctly?

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        #4
        Yamaha's oil injection system is gear driven and very reliable. Over oiling from pre-mix plus injection shoulder cause an idle problem until the plugs foul. Id run some seafoam in your next tank of fuel.

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          #5
          Originally posted by Walker View Post
          Yamaha's oil injection system is gear driven and very reliable. Over oiling from pre-mix plus injection shoulder cause an idle problem until the plugs foul. Id run some seafoam in your next tank of fuel.

          Thanks. I’ve been seeing similar comments in the various outboard forums. I think I’m gonna fill the oil tank tomorrow and put a fresh tank of gas in and see how she does.


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            #6
            Thanks for that info Walker . I have a 2004 115 2 stroke I’ve had for about 2-3 years and I’ve worried about the oil injection. I have replaced the strainer at the bottom of my main oil reservoir on my boat. Sorry , didn’t mean to Hijack thread
            Last edited by HotRod Hunter; 03-27-2021, 07:26 PM.

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              #7
              Any alarms going off?? There should be a low oil sensor on the oil tank. The previous owner may have unplugged it. You need to check the small oil line coming from tank to pump and from pump to carbs. The is a metal rod from the pump to the carb linkage to needs to be connected also. All this stuff is on the port side of the motor. You might Google it for pictures or u-tube.

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                #8
                Oil pumps are solid-
                The lines just suck.. they crack

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                  #9
                  Running rough sounds more like a low speed jet(s) that need to be cleaned. I bypassed my oil pump just because I would rather not take the risk of it malfunctioning 30 miles from the ramp in marshes not other boats I know can get to. Just a little piece of mind.

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                    #10
                    Ive got a 2001 yamaha 70. Blew the motor about 6 years ago due to water that had gotten into the oil reservoir through the rubber gasket around the oil cap on top of the cowling. First thing my yamaha mechanic did was bypass the injection system after rebuilding. Ive been mixing oil ever since with zero issues

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                      #11
                      If he was running regular fuel with any ethanol in it - it would also cause it to run rough. Be sure to run an ethanol fuel stabilizer in a two stroke...

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                        #12
                        My lines all look fine, no signs of any cracking. Filled 16 gallons in the gas tank today so that leaves 8 in there with some pre-mix. Went ahead and topped off my oil tank and also added seafoam to the gas. Motor ran like a champ all morning and is idling much better. This boat had been stored for a very long time. Previous owner had it serviced last summer but no telling how old the gas in the tank was. I think I’m now past any old gas issues too.



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                          #13
                          Not sure if Yamaha & Evinrude are the same but I have a 1997 Evinrude 70 HP. Mechanic I trust recommended disabling the VRO pump and adding a traditional vacuum operated diaphragm fuel pump and start mixing oil in the gas tank. It has run great ever since & gets better fuel mileage. If the previous owner said to mix oil in gas, maybe he did the same thing?

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                            #14
                            Originally posted by Monark View Post
                            Not sure if Yamaha & Evinrude are the same but I have a 1997 Evinrude 70 HP. Mechanic I trust recommended disabling the VRO pump and adding a traditional vacuum operated diaphragm fuel pump and start mixing oil in the gas tank. It has run great ever since & gets better fuel mileage. If the previous owner said to mix oil in gas, maybe he did the same thing?
                            They're not the same. Omc was crankcase pulse powered (vacuum). Yamaha has a gear driven pump.
                            Last edited by Walker; 03-28-2021, 04:36 PM.

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                              #15
                              I had a 1988 70hp Yamaha I ran for years (on 3 different boats) and never had an issue with the oil injection. I sold it a few years back but I bet it’s still going strong.

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