2003 135h.p. optimax

I was out fishing this weekend and my motor was acting up. I lost around 900 r.p.m. and also around 5-8-m.p.h. any idea what to look for? I put new plugs in and that did not help

Mine did the same thing on leech 2 days ago only I lost 300 rpm and 2 to 4 mph, gonna find out tomarrow if it was a one time deal or a problem. I was wondering maybe the gas has some thing to do with it, need to find some 93 non-ox and just stay with that.mine is a 05 135 optimax

Replace the fule filter first If that dont do it go in and get it scanned its cheap and it will tell you everything you should know about your motor!

Could be a number of things plugged injector, loose injector wire, even new plugs I have some that were bad right off the get go.

Are you letting that Opti warm up before putting the hammer down, cold lock is the number one cause of Opti problems.
Get it scanned like DCO mentioned quickest way to find out.

I have a 135 Opti and gas has never been an issue and most of the gas I run is 10% ethenol and never had a problem from gas. My manual does not recommend 93 octane.

Like Tom said.
Just oddball question here, how is the prop? Any dings or hits lately? That can drop the RPM’s and speed as well-even minor dings and hits.

Might not be anything wrong with the motor. May be a comination of hot weather and ethonol gas. I always notice a performance drop during these summer day temps. The comment about the 14% drop would translate to about a 900 rpm decrease in your rpms.

Is it possible you added some E-85 to your tank? Or maybe the station “Slipped” you some gas with an errant mix??? You may want to add premium – “non-oxy” gas nect trip to the pump.

Try getting out before sun up when the air is still somewhat cool and give er’ a run down. See if you have the rpm and speed to start the day. Good luck.

From the merc website:

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Why does my boat perform differently on a hot day verses a cool evening?

It is a known fact that weather conditions exert a profound effect on power output of internal combustion engines. Therefore, established horsepower ratings refer to the power that the engine will produce at its rated rpm under a specific combination of weather conditions.

Corporations internationally have settled on adoption of I.S.O. (International Standards Organization) engine test standards, as set forth in I.S.O. 3046 standardizing the computation of horsepower from data obtained on the dynamometer, correcting all values to the power that the engine will produce at sea level, at 30% relative humidity at 70 deg.F (20 deg.C) temperature and a barometric pressure of 29.61 inches of mercury.

Summer Conditions of high temperature, low barometric pressure and high humidity all combine to reduce the engine power. This, in turn, is reflected in decreased boat speeds–as much as 2 or 3 miles-per-hour (3 or 5 Km per-hour) in some cases. Nothing will regain this speed for the boater, but the coming of cool, dry weather.

In pointing out the practical consequences of weather effects, an engine–running on a hot, humid summer day–may encounter a loss of as much as 14% of the horsepower it would produce on a dry, brisk spring or fall day. The horsepower, that any internal combustion engine produces, depends upon the density of the air that it consumes and, in turn, this density is dependent upon the temperature of the air, its barometric pressure and water vapor (or humidity) content.

Accompanying this weather-inspired loss of power is a second but more subtle loss. At rigging time in early spring, the engine was equipped with a propeller that allowed the engine to turn within its recommended rpm range at full throttle. With the coming of the summer weather and the consequent drop in available horsepower, this propeller will, in effect, become too large. Consequently, the engine operates at less than its recommended rpm.

Due to the horsepower/rpm characteristics of an engine, this will result in further loss of horsepower at the propeller with another decrease in boat speed. This secondary loss, however, can be regained by switching to a smaller pitch propeller that allows the engine to again run at recommended rpm.

For boaters to realize optimum engine performance under changing weather conditions, it is essential that the engine have the proper propeller to allow it to operate at or near the top end of the recommended maximum rpm range at wide-open-throttle with a normal boat load.

Not only does this allow the engine to develop full power, but equally important is the fact that the engine also will be operating in an rpm range that discourages damaging detonation. This, of course, enhances overall reliability and durability of the engine.

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and…

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Does ethanol affect horsepower or fuel-efficiency?

Ethanol has a heating value of 76,000 BTU per gallon, which is approximately 30 percent less than gasoline’s heating value (which is approximately 109,000 to 119,000 BTU/gal). The result is E-10 gasoline which should yield slightly lower mileage – a decrease of approximately 3 percent. Fuels containing higher levels of ethanol will have a corresponding reduction in mileage. For example, E85 fuels produce mileage approximately 30 percent less than gasoline.

The octane rating of pure ethanol (200 proof) is about 100 and is therefore useful in elevating the octane value of gasoline. In E-10 blends the presence of ethanol provides about 2.5 to 3 percent of the overall octane rating. The effect on engine horsepower is determined by the octane result of the blended fuel. Care should be taken to select fuels having the octane rating recommended for the engine as indicated in the owner’s manual for proper operation.

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-J.