oil to fuel ratio needed

[runningbear888]

Could someone tell me the proper oil to fuel mixture for a 1976 115 hp Mercury outboard? Also, how fast should this motor push a 16.5 foot fiberglass boat? The boat runs at about 28 mph with 2 people in it, when one person goes to the back of the boat it picks up another 4-5 mph. Thanks for your help.<br /><br />Runningbear.

 

[andrewkafp]

Re: oil to fuel ratio needed

50:1 MIX <br /> http://www.goa-northcoastoil.com/tips/obmixing.html

 

[ZmOz]

Re: oil to fuel ratio needed

For most merc engines mercury says 50:1. I have a '74 150hp, and I usually mix 50:1 and then add a little extra. Too much just causes more smoke, too little will ruin your engine quite quickly.

 

[The Marine Doctor]

Re: oil to fuel ratio needed

Too much will carbon the engine up and ruin it.<br /><br />Just mix as directed.<br /><br />TMD

 

[andrewkafp]

Re: oil to fuel ratio needed

Agree with TMG..<br />Try to get it right on.. Use the chart. <br /> http://www.tohatsu.com/tech_info/oil_gas.html <br />You gotta keep those carbs clean and the Air/Fuel mix right to avoid burning pistons.<br />Too much oil can clog things up and affect the motor. The short term visual effect is more smoke, but in the long term more problems will arise.

 

[bergsofafeather]

Re: oil to fuel ratio needed

rb888, There's a lot to be said about prop size and pitch and all, perhaps someone else can give you the scoop on this, and of course the weight of your boat and motor, .....but just a comparison, I run a 1975 85hp Merc on a 1976 Bayliner Mosquito (15.5') and turn 34 mph consistently. I do know that you will get better performance by being heavier aft of center, thus keeping the bow light making for better planing. If all else fails, throw in another couple of gas tanks in the butt!

 

[ZmOz]

Re: oil to fuel ratio needed

More oil will give you more carbon...but doing 50:1 and then adding a little extra that might bring you to 40:1 isn't going to be a noticeable difference, although the chance that you didn't get enough oil is much lower. Mercury used to recommend 25:1 for their racing engines didn't they? You should run something like seafoam through your engine regularly anyway.