Mercury 4HP 1978 Belgian, Fuel Ratio?

[bassmandan89]

Hello everyone, I have a 1978 Mercury (40) 4HP outboard 2 stroke, 2 cylinder. I called my local boat dealership for the fuel/oil ratio and they werent really sure off hand but that it was probably 50:1 ratio. I just bought a 3 gallon tank and some 2 cycle oil (1 pint 16 ounces) and needed to know for sure how much oil to put in the tank if i indeed fill up the 3 gallon tank?<br />I appreciate any help you can give me, thanks

 

[Paul Moir]

Re: Mercury 4HP 1978 Belgian, Fuel Ratio?

Welcome to Iboats, bassmandan!<br /><br />The mixture for that outboard is 50:1 87 octane gas to TC-W3 rated outboard oil. That works out to 1/2 pint for your 3 gallon tank, or to say it another way 1/4 of your quart of TC-W3.<br />By the way, the plugs recommended for that engine in the US were Champion QL7J5 or QL7J gapped at .050". In the rest of the world, they recommended NGK RB6HS gapped at .050. I find the NGK ones work better in it. I don't use the NGK B6HS plugs because they cause a lot of radio interference, but they work equally well.<br /><br />I've been through he11 and back with one of those little 4hp Merc Gnats. If you need any help, just say the word!<br /><br />Good luck!

 

[bassmandan89]

Re: Mercury 4HP 1978 Belgian, Fuel Ratio?

Thanks Paul, this info really helps.....so far i only have 150.00 in the mercury outboard and i have seen it run and run real well but i didnt know the ratio myself. thanks again for all your help, and i will call on you again if i need to.<br /><br />Dan M.

 

[Paul Moir]

Re: Mercury 4HP 1978 Belgian, Fuel Ratio?

Good to hear!<br />It's really a high tech outboard for a 4hp there - looper with through-prop exhaust, F-N gearshift, nickasil bores, needle and roller bearings throughout. Pretty much the opposite of the circa 1950 design 4hp iron bore crossflow with no shift that OMC offered at the time. <br />It's also a strong engine - my brother uses his to push around his sailboat.