Yamaha 9.9 oil/gas issue

[FishingFool34]

2002 Yamaha 9.9 4-stroke... came with the boat I bought, previous owner warned me it was cold blooded but it ran fine during sea-trial so I bought the boat. First time out with it this weekend and took forever to start. Once I finally got it started it would idle but die everytime I hit the throttle. I could choke it and get it to rev up but as soon as I gave it throttle it would die. Got it back home and happened to pull the dip stick and it poured out oil/gas mixture out of the dipstick hole. Did I just severely flood it trying to get it running or do I have other issues?  

[tech2526]

I have an 01 and it is also a cold blooded four letter word. But your carb may be leaking. Give it an oil and spark plug change and try again. Over full oil mixed with gas can cause several problems. One will be low compression. Causing it to stall with any load.

 

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[mr 580]

I have a 03 9.9 Yamaha and it is hard to start too.  Mine doesn’t have a choke knob.  What I do is leave my big motor idling in gear then put 9.9 in gear to open/close throttle multiple times then back to neutral to start.  It usually will then start 1st pull and I let it run a bit before putting in gear-it tends to not want to take load at first and it might stall.  Once it takes load, it runs without an issue for hours.  In the fall I run it out of fuel by disconnecting fuel line-since I’ve done that it starts 1st pull in spring again.  As far as fuel in oil issue- that sounds like stuck float or needle/seat leak.  I’d pull carb and clean.  I don’t see excess fuel in oil when I change.  I have an 8 hp Yamaha on my other boat and both of them have been good.  Never use oil and run forever.  I do run non-ethanol fuel and conditioner at all times.  With a carb clean and figuring out a start procedure then you should be fine.

[tuffishooker]

Ditto on the no ethanol fuel and  " additive " ; remove the drain plug on the carb and drain [may solve the problem ] . I always filter my gas before putting the fuel in the tank . I always run the carbs out of fuel after use but I have heard different opinions for this in storage esp lawn mowers !

[emtystringer]

If motor was laid on its side when transporting it may have been laid on the wrong side  . it can only get laid on one side or oil and gas will mix 

[Sk8man]

If the choke was left part way out without being detected and the motor was run for quite awhile it could do that. Apparently some motors may also need a different thermostat than the one that came with the motor appropriate for the specific climate temperatures encountered they are operating in. Not  sure if this is an issue with it but it is something that a tech guy mentioned to me in the past.  Overfilling of oil sounds like a possible contributor. Sometimes the oil level needs to be filled to just below the upper level on the stick as the oil may become more viscous when warm and then exceed the upper level and if the choke was left on or partially some mixing with the gas may have occurred and have the look of "unburned" fuel turning the oil black.

[mr 580]

You might try changing the oil and running it in a garbage can full of water.  If you have a separate tank put a gallon of gas with an extra dose of Sea Foam in it - might get carb cleaned w/o taking it apart.  Run it for awhile and check oil level.  Once you find a starting procedure the motor “likes” should be ok.  My experience with the little Yamahas is that they are bullet proof and require little maintenance.

[Frogger]

X2 the changing oil / plugs and running it in a bucket while sea foaming it.


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[Jack]

May have nothing to do with your problem but my neighbor had the same issue . Gas in the oil. Turns out he bought a new fuel tank which are now sealed they have a vent to let air in but not out. So the sun would heat up the tank and force the gas into the motor. I also believe Yamaha's have a sensor that won’t let them run if there is to much oil (and gas) in the crankcase. He had to add a pressure relief valve to his fuel line. 

[Jack]

These motors run very lean. I removed the small plug on the carb that covered the needle valve and richen it up . Because these do run so lean it doesn’t take much dirt or fuel deposits to restrict the gas flow and make them run poorly. 

Good luck

 

[sullyonhudson]

Your fuel pump diaphram has failed.  This allows gas to be pumped into the oil, hence the release of pressure when the dipstick was removed.  Replace the fuel pump ( very easy job ).  Drain the oil and replace with fresh.  Run the engine at idle to heat up the oil.  Drain oil again and put in fresh.  You want to get as much of that gas out of the crank case.

[p3434]

I agree the fuel pump failed. i have a 9.9 nissan 4 stroke. Last year , I was getting gas in my oil. Pulled the carbs and cleaned them. Had the same problem. Then I bought a new fuel pump online , and installed it. no more gas in the oil.

[David435]

Had the same problem with my Yamaha 9.9 For a long time it was very hard starting then I see there was gas in my oil. Changed the pump and all my problems were solved. Got the parts from Boats.net  Excellent people and service. In fact I bought a new 150 Merc 2 years ago for my boat from them couldn't be happier. Saved thousands.