What fuel mixture for 2001 115hp mercury 2 stroke salt water series

[wild card]

I just purchsed a 17 foot Mako with a Mercury 115hp 2001 2 stroke saltwater series. The boat doesnt have any manuals. The previous owner said that it runs on 50:1 straight from the fuel tank. Any advice would be appreciated. I thought by 2001 most outboards were using 100:1. When I test ran it she ran pretty rough. Any information would be appreciated Im just getting going on this and dont have much experience with big outboards. I am still trying to figure out if its carbs. or fuel injection. Thanks john

 

[Silvertip]

Re: What fuel mixture for 2001 115hp mercury 2 stroke salt water series

To determine if the engine is EFI or carbed, remove the engine cover and look. Carburetors will be looking at you as face the engine from inside the boat. They wil be behind the air intake silencer. You are wrong about the 100:1 pre-mix ratios. Mixtures have been 50:1 for decades. You remove the cover of your engine. You check for presence of an oil resevoir. If it is not there, you MUST mix fuel in the tank at 50:1. If the tank is there, check to see if it is plumbed and wired properly and that the oil injection pump is installed. If it is, verify that the system is operating. If it is, there is no reason to pre-mix fuel. As for rough running, you should know this engine idles on two cylinders and the other two cut in as you apply throttle. That feature may have been eliminated by the previous owner. Unless the engine cover says OptiMax on the cover, it is not fuel injected.

 

[ticondo46]

Re: What fuel mixture for 2001 115hp mercury 2 stroke salt water series

WildCard,


Out of interest,I have monitored actual oil percentage delivered on my Mercury 115 2-Stroke since I bought it in 1997. Year on year, the exact percentage delivered by the automatic oil feed runs steadily around 1.5 %, i.e. 65:1. May I add that no alteration whatsoever was ever done to the factory settings, and that the motor works absolutely fine on this concentration. No point pre-mixing if the oil pump, reservoir and pipings are in place and in good working order. If not, and if pre-mix is chosen, 100:1 would be a bit dry. 50:1 would do absolutely no harm however, other than fowling up the plugs slightly faster.

Regarding the carbs and their weird setup, there are a lot of threads on this forum explaining in detail how they work. If you can't find them, give a shout, I will redirect you.

 

[phebus1]

Re: What fuel mixture for 2001 115hp mercury 2 stroke salt water series

The automatic system is variable, depending on throttle setting. I wouldn't suggest that someone pre mix at 65:1, much safer to stay at the recommended 50:1.

 

[Texasmark]

Re: What fuel mixture for 2001 115hp mercury 2 stroke salt water series

The automatic system is variable, depending on throttle setting. I wouldn't suggest that someone pre mix at 65:1, much safer to stay at the recommended 50:1.

The manual for that engine states 80:1 at idle varying to 50:1 at WOT via the pump.

 

[ticondo46]

Re: What fuel mixture for 2001 115hp mercury 2 stroke salt water series

Good point; however, just for argument's sake, how much Wide Open Throttle do we do on a 115? In my experience, maybe a few minutes a week, no more. On my 17.5 ft boat, a comfortable well-planed cruise will be at 3,000/3,200 RPM. Beyond that, it would take a very flat sea to go WOT. That doesn't happen every day. 50:1 is really a bit smokey. Let's do something for the marine environment! Lean is clean!

Jut one word of caution, WildCard: if you plan to use the autolube feature, make sure the oil pump is thoroughly checked and primed beforehand. I would be concerned if the previous owner never used it, because inside, the pump is composed of two nylon gears that are driven off the crankshaft. Those gears don't like running dry for any extended period of time. And priming the oil circuit is of essence, because the gear pump hardly creates enough vacuum to suck the oil. Don't assume that the oil will travel on its own just by filling the oil tank. The circuit has to be filled beforehand.