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Old 03-27-2021, 07:33 PM   #1
TexaRican
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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 didnít ever run this boat and donít 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 doesnít like to idle for more than a minute or two without stopping. No issue restarting on first turn. Wondering if Iím oil rich now cause there was oil in the oil tank being mixed with my already 50:1 gas tank?


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Old 03-27-2021, 07:40 PM   #2
manwitaplan
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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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Old 03-27-2021, 08:13 PM   #3
easeup
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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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Old 03-27-2021, 08:14 PM   #4
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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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Old 03-27-2021, 08:18 PM   #5
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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. Iíve been seeing similar comments in the various outboard forums. I think Iím gonna fill the oil tank tomorrow and put a fresh tank of gas in and see how she does.


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Old 03-27-2021, 08:22 PM   #6
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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

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Old 03-27-2021, 08:29 PM   #7
Walker
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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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Old 03-27-2021, 09:12 PM   #8
kingranch
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Oil pumps are solid-
The lines just suck.. they crack
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Old 03-27-2021, 11:24 PM   #9
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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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Old 03-28-2021, 04:05 AM   #10
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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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Old 03-28-2021, 08:50 AM   #11
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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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Old 03-28-2021, 04:19 PM   #12
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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 Iím now past any old gas issues too.



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Old 03-28-2021, 04:57 PM   #13
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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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Old 03-28-2021, 05:03 PM   #14
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Quote:
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 at 05:36 PM.
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Old 03-28-2021, 06:32 PM   #15
bowhntrmatt
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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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Old 03-28-2021, 08:03 PM   #16
TexaRican
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Quote:
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?

Previous owner pretty much passed the boat though to me with a signed title from the original owner. He said as I was driving away always mix gas and never trust a oil pump. I texted him later asking if there was already pre-mix in the tank and he replied that he didnít know.
This guy had a barn full of toys- RV, UtV, ski boat, Jeepís, 4 wheelers. I think he bought this boat and it sat under a cover for a year or so that he had it.


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Old 03-28-2021, 08:12 PM   #17
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If that's all the history you have then I suggest you put a new waterpump in it.
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Old 03-28-2021, 08:37 PM   #18
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Yeah the guy claimed he had a full service done. Asked him if that included the impeller and he said no. I replaced it but the one that was in there looked brand new. Spark plugs look brand new. I think this guy just didnít have a clue.


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Old 03-28-2021, 08:38 PM   #19
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Good deal.
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Old 03-28-2021, 08:42 PM   #20
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Personally I’d just pre-mix it unless the boat is kept in the water and fueled at marinas. Getting gas there is enough of a hassle that I wouldn’t want to comokcsfe it more by having to add a precise amount, and dealing with oil bottles/trash.
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Old 03-29-2021, 03:37 AM   #21
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I have never had any issues with a oil injection system on any Yamaha outboard. Not saying that it doesn't happen but I do not worry about it. I have had 2 Yamaha 70 HP 2 strokes (flatbottom), a 150 HP HPDI (bayboat), and twin 200 HP HPDI's (offshore boat) over the past 25 years, never 1 issue with any of them. I may have just gotten lucky but all my buddy's that run 2 stroke Yamaha's haven't had issues either. Yamaha makes a heck of a motor in my opinion/experience.
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Old 03-29-2021, 07:01 AM   #22
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Mine is a 02 200 Yamaha never think about it. I no that omc had problems . And if I ever have any questions I know you too reach out to
Walker sounds like he knows his ****z


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Old 03-29-2021, 08:11 AM   #23
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Quote:
Originally Posted by Snowflake Killa View Post
Walker sounds like he knows his ****z


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Sho'nuff! Thanks again Walker. You helped me a bunch on my mercruiser thread getting my bayliner tuned up for sale.
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