90 HP Yamah***

[LittleSmoky]

We are having problems with our 90 HP Yamaha fouling plugs. (Light coating of oil on them).<br />Is removing the oil injection system an option ( I think its getting too much oil) and just mixing the gas and if so should it be 50:1. Comp readings were 98,95,92 from top to bottom. Should we be using a higher grade of gasoline possibly. Any ideas would be greatly appreciated.<br /><br />Thx <br /><br />Smoke

 

[butlp]

Re: 90 HP Yamah***

LittleSmoky,<br />Your compression seems a little low (should be around 120 psi), however they are very similar pressure. Your compression tester gauge maybe reading low.<br />I believe the Yamaha oil injection is one of the best and therefore I would recalibrate before disconnecting completely.<br />I strongly suggest you get the Yamaha maintenance manual for your motor and perform the full service of carb's, ignition and oil pump calibration. <br />I did mine this summer and it now runs great.<br />Hope this helps.<br />Peter

 

[Forktail]

Re: 90 HP Yamah***

Just keep track of how much oil you use per gallon of gas. That will give you your ratio. 2-strokes run around 50:1 and not much more. I've seen some below 40:1 that were fine. But some of these newer 2-strokes run extremely oil lean. You will need to find out exactly what ratio this engine is designed to run on (dealer). Keep in mind that your ratio will change slightly depending on what throttle range you are running at. Very few oil pumps run linear to fuel usage.<br /><br />There is 16 oz in pint. 2 pints in a quart. 4 quarts in a gallon.<br /><br />So each gallon has 128 oz. <br /><br />For a 50:1 ratio, divide 128 oz by 50. You get 2.56 oz.<br /><br />So for each gallon of gasoline, you should be using 2.56 oz of 2-stroke oil, for a 50:1 mix.<br /><br />For a 100:1 mix you would divide 128 by 100. This would be 1.28 oz oil per gallon.

 

[Solittle]

Re: 90 HP Yamah***

I suspect your manual calls for 87 octane and if so that is what you should use. Check "Search Forums" in red above as this has been discussed at length many times.