oil ratio

BillPutney · #1 07-02-2009, 05:30 PM

What is the correct oil/gas ratio for a 91 70 hp. Mercury outboard. The boat belongs to a friend that just bought it from a mechanic who told him to put double the normal amount of oil for the first tank and 1.5 times the amount on the second tank during break in period.

bridgeman · #2 07-02-2009, 08:18 PM

If the oil injection is hooked up you'll need to pre-mix 50:1. I'd run it that way for a 20 hrs or so, won't hurt anything other than fowl the plugs if you idle for extended periods.

eggsuckindog · #3 07-03-2009, 03:26 PM

Normal 50/1 as mentioned if oil injected judt put another 50/1 in the tank - if not then run it at 25/1 premixed

BillPutney · #4 07-03-2009, 08:16 PM

I told him to add 50 oz. to 10 gals for the first go round.That should be close enough don't you think ?

BillPutney · #5 07-03-2009, 08:17 PM

The motor ie not an oil injected model

bridgeman · #6 07-04-2009, 08:08 AM

If the motor is not oil injected you need to run 25:1 initially eg. 1 gallon of oil added to 25 gallons of gas for at least the first 10 hours, I'd go 20 hrs and lean it up after that.

BillPutney · #7 07-04-2009, 09:20 AM

If my math is right the 50 oz. to 10 gals works out to 1 gal. oil in 25.6 gals. gas . Glad you confirmed that for me.