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2002 Newly Rebuilt Yamaha 90hp 2stroke

2K views 12 replies 5 participants last post by  justletmein 
#1 ·
Can anyone tell me if I should be running twice the normal amount of 2 stroke oil during the break in period of this motor? Does anyone have the Yamaha recommended procedure for breaking in a fresh rebuild 90hp 2stroke.

I really don't want to mess this up!
 
#2 ·
Yes, you need to run double the amount of oil...25:1...the first 30 gallons of fuel. Vary the throttle up and down in the rpm range with no full throttle...keep it at 3/4 throttle max...for the first couple of hours. After this, keep varying the throttle and full throttle may be attained shortly. After 30 gallons of fuel, you can then go to the regular 50:1 mix of oil...or just none in the fuel tank if you've left the oil injection, but frankly, I would disconnect it on a Yamaha...and then again no sustained full throttle for the next 5 hours.
 
#3 ·
I should have said, yes, I deleted the onboard oiling system. I will be pre-mixing from here on out. I put 16 gallons of fresh non ethanol in the tank and pre-mixed it to a 40 to 1 ratio. The tank will hold an additional 10 gallons, but I hate filling it up because of the weight. Boat is a 16' custom aluminum flats boat.

I'm getting conflicting info about the fuel/oil ratio. I'd rather err on the side of caution.
 
#6 ·
Thanks Bwguardian.

I located the break in instructions for my motor from Yamaha. Essentially they want you to pre-mix your fuel at 50:1 and run it through with their automatic oiling system which adds more oil effectively reducing that ratio to 25:1.

Since I had the on board oiling system deleted, I'll just mix my current batch of fuel at 25:1 and be done with it.

I picked up and pre-gapped 6 new NGK B8HS-10 spark plugs to keep on hand as I suspect I'll foul them during this process.

So rather than toss the fouled plugs, shouldn't I be able to clean them up and re-use them? At $2.49 apiece, they don't break the bank if I decide not to keep 'em.
 
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