Gas Ratio

[dplatt]

I just have a simple question, I have a mercury 2.2 hp on my jon boat that was givin to me, I think its pretty old like maybe a 1980 or so and I need to know what fuel/oil mixture should be. thanx

[a64pilot]

All two stroke outboards that I know of have always been 50 to 1, having said that I would also use only a TC-W oil, they are made for marine engines, I don't know the difference between that and weed eater two stroke oil though.
If you run it a little richer, it won't hurt anything, maybe foul a plug sooner, but no harm. I run all my two stroke motors richer than 50 to 1, personal preference.

[captainstubbie]

When I bought my early 1980's mercury outboard, the tag on the engine said 40 to 1 ratio. Have been using that ratio since purchase with no problems.

What say you?

[brantleychuck]

I thought the same thing about adding a little extra oil to the 2 stroke mix . What could it hurt? But a friend of mine explained a possible issue with doing that. By adding extra oil to the gas oil mix you are essentially leaning the air/fuel mixture. A side effect of a more lean mixture is hotter combustion temperatures which can cause damage to pistons and such. Best to stay with the manufactures oil gas ratio and a good quality oil. But not a big deal in any case. As a side note the easiest sway I have found to measure oil for mixing is the bottle with the cap and all the ratio markings on the side. Easy to keep things clean.

[cal40john]

Almost certainly 50 to 1, especially for that era, but just to be a pain I have an older friend who remembers 25:1, the first link says that 60s and older used that ratio. I remember the last 2 stroke our club keelboats had was 100 to 1. I think I remember a club 40 hp that said 40 to 1 as well.

Service Frequently Asked Questions What is the correct ratio for mixing oil and gas for my outboard motor?


Oil Mix Ratio


Mercury service manual link below says 50:1, don't know what years it covers. see page 1-2

Boatinfo - Mercury Service Manual for 2,2-2,5-3,0-3,3 hp

[PommyDave]

I have a Mercury 8hp outboard. The manual says to use 25:1 while breaking-in a new motor for the first ten hours use. Then can use 50:1 ratio fuel. You do this by keeping the revs low for the first 10 hours use. Mine was purchased in 2003.

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[FSMike]

Originally Posted by brantleychuck

I thought the same thing about adding a little extra oil to the 2 stroke mix . What could it hurt? But a friend of mine explained a possible issue with doing that. By adding extra oil to the gas oil mix you are essentially leaning the air/fuel mixture. A side effect of a more lean mixture is hotter combustion temperatures which can cause damage to pistons and such. Best to stay with the manufactures oil gas ratio and a good quality oil. But not a big deal in any case. As a side note the easiest sway I have found to measure oil for mixing is the bottle with the cap and all the ratio markings on the side. Easy to keep things clean.

brantleyc -

I disagree.
First leaning out the fuel mixture is properly referred to as leaning out the fuel/air ratio, leaner being more air less fuel mixture (gas & oil).

Back in the days when I was racing motocross bikes the idea was that leaning out the oil/gas mixture (less oil more gas) would increase horsepower since it was the gas that really provided the "bang". That was popular for a while until somebody discovered that increasing the oil percentage helped the engine run cooler, which increased the hp.

So instead of reducing the oil until the engine was in danger of seizing all the racers increased the oil until the engine was in danger of fouling a plug when you tried to start it. Had to use a hot plug to warm up the engine, then switch to a normal heat range to race with.

Now that I've said all that I have to admit that I'm not sure how this info from highly tuned air cooled motorcycle race engines applies to water cooled dinghy kickers lol.

[denverd0n]

You can probably look up the correct mixture. Find the model number--it is bound to be on the engine somewhere; practice a little google-**; et voila!

I have an old Johnson 2.5 and after a half hour or so sorting through Google results I was able to find a parts manual that included all the specifications, including recommended fuel/oil mixture (which, for that particular engine, was 40:1).

Good luck.

[1000 islands]

50:1 is the most common mixture for 2 stroke engines.

By enriching the mixture two things will happen, first you will foul your plugs real fast and the engine will smoke, stink and cause much more pollution.

[Dockhead]

Originally Posted by FSMike

brantleyc -

I disagree.
First leaning out the fuel mixture is properly referred to as leaning out the fuel/air ratio, leaner being more air less fuel mixture (gas & oil).

Back in the days when I was racing motocross bikes the idea was that leaning out the oil/gas mixture (less oil more gas) would increase horsepower since it was the gas that really provided the "bang". That was popular for a while until somebody discovered that increasing the oil percentage helped the engine run cooler, which increased the hp.

So instead of reducing the oil until the engine was in danger of seizing all the racers increased the oil until the engine was in danger of fouling a plug when you tried to start it. Had to use a hot plug to warm up the engine, then switch to a normal heat range to race with.

Now that I've said all that I have to admit that I'm not sure how this info from highly tuned air cooled motorcycle race engines applies to water cooled dinghy kickers lol.

That's the opposite of what snowmobile racers say. They say that indeed too much oil can burn a piston, as it replaces fuel making the mixture leaner and burning hotter.

I think completely irrelevant to us, though -- dinghy outboards are so low powered compared to these that there is just no way you will burn a piston.

My snowmobile makes 120 horsepower out of 600cc, and it's not even a racing sled. This is like 10x the specific power of a typical outboard.

A bit of thread drift -- it's a Rotax direct injected engine which weighs less than my 8hp dinghy outboard. It does not behave like a high strung racing engine at all -- broad torque curve and max output at moderate 8000 RPM. An amazing power plant. Makes you think that two stroke engines still have some development potential.

[zeehag]

your mix will be either:
100 : 1
50:1
25;1 or 40 ; 1. it is a good idea to research by use of dealer/distributor if in doubt. nothing like destroying your engine because some one said to use the wrong mix. too much oil is not as bad as not enough, but you want the correct mix for your engine. in the mean time, a lil extra lubing wont kill it. make it a lil sluggish if anything, but i didnt even experience that issue with overoiling my new to me engine , some years ago.

[Cheechako]

My Yamahas were stated as 100:1. Others as low as 40:1. I just mixed some where in the 80:1 range for the Yamaha.

[MarkJ]

I had a mercury 3.3 and it was 50:1