2008 Yamaha T60 lacking power, especially at elevation

[DAPSRT]

I have a 2008 Yamaha fuel injected T60 4 stroke on an 18 foot Koffler custom built boat. The engine runs great most of the time but it has been acting up intermittently over the last couple years but especially when it is at elevation (6000+ feet). That being said it hasn't been perfect, even at sea level, either. One shop I took it to said it was the injectors and cleaned them at a cost of $400 plus. It worked ok for a while and then began acting up again.

When it happens, the engine won't turn over 3200 rpm (give or take a tad) but the engine runs smooth. It seems to be running out of fuel but there is plenty in the tank and filters are new. Running clear 92 octane for fuel, never run any ethanol through it. Has new plugs, and doesn't change when the fuel bulb is pumped. Tanks are 6 gallon portable tanks in the front of the boat, hose running to the back under the deck, through a water separating filter and then to the engine.

Seems to me that because the problem is intermittent, it can't be a plugged filter. Screen in the fuel tanks is ok, tanks are clean.

Any suggestions? Thanks!!

 

[T_Herrod]

Re: 2008 Yamaha T60 lacking power, especially at elevation

You say the fuel tanks are in the front of the boat and the fuel has to travel 18 feet through a filter to reach the engine. I would be looking at the fuel line to see if it has soft spots that could create a restriction.

 

[boscoe99]

Re: 2008 Yamaha T60 lacking power, especially at elevation

Based on the size of the fuel line, and the distance from the tank to the motor, you might have an excessive restriction to fuel flow. As T notes, if the fuel line is degraded it will only make things worse. Put a vacuum gauge into the fuel line just aft of the fuel filter cup. Between the fuel filter and the fuel pump. See what the vacuum reading is at WOT and let us know.

Or, just install a small one gallon tank connected close to the motor as a temporary test device. If the motor runs well with the small close by tank but not with the distant tanks, there is your issue.

High altitude is a different problem. At 6000 feet the motor is not making anywhere near rated power. If you were marginally propped to begin with it is made worse at altitude. You might need a different propeller with lesser pitch. Here is what Mercury Marine says about high altitude ops.

How do elevation and climate affect performance?

Elevation has a very noticeable effect on the wide-open-throttle (WOT) power of an engine. Since air (containing oxygen) gets thinner as elevation increases, the engine begins to starve for air, like using a supercharger in reverse. If the boat has been set up at a lower altitude and then moved to a much higher altitude, there will be a noticeable reduction in power, thus RPM.

Although some performance can be regained by dropping to a lower-pitch propeller, thus bringing the WOT RPM back into the recommended range, a basic problem still exists. The propeller is too large in diameter for the reduced power output. The experienced marine dealer or a Quicksilver propeller repair station can determine how much diameter to remove from a lower-pitch propeller for specific high-elevation locations.

In some cases, a gear ratio change to more reduction is possible and very beneficial. However, this fix is only safe while the power level is reduced. If the engine is again run at a lower altitude, the gear ratio change must be reversed to prevent excessive torque on drive train parts.

It is a fact that weather conditions exert a substantial 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 now established by the International Standards Organization (ISO).

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 two or three miles per hour in some cases. Nothing will regain this speed for the boater, but the coming of cool, dry weather.

 

[DAPSRT]

Re: 2008 Yamaha T60 lacking power, especially at elevation

Based on the size of the fuel line, and the distance from the tank to the motor, you might have an excessive restriction to fuel flow. As T notes, if the fuel line is degraded it will only make things worse. Put a vacuum gauge into the fuel line just aft of the fuel filter cup. Between the fuel filter and the fuel pump. See what the vacuum reading is at WOT and let us know.

Or, just install a small one gallon tank connected close to the motor as a temporary test device. If the motor runs well with the small close by tank but not with the distant tanks, there is your issue.

High altitude is a different problem. At 6000 feet the motor is not making anywhere near rated power. If you were marginally propped to begin with it is made worse at altitude. You might need a different propeller with lesser pitch. Here is what Mercury Marine says about high altitude ops.

How do elevation and climate affect performance?

Elevation has a very noticeable effect on the wide-open-throttle (WOT) power of an engine. Since air (containing oxygen) gets thinner as elevation increases, the engine begins to starve for air, like using a supercharger in reverse. If the boat has been set up at a lower altitude and then moved to a much higher altitude, there will be a noticeable reduction in power, thus RPM.

Although some performance can be regained by dropping to a lower-pitch propeller, thus bringing the WOT RPM back into the recommended range, a basic problem still exists. The propeller is too large in diameter for the reduced power output. The experienced marine dealer or a Quicksilver propeller repair station can determine how much diameter to remove from a lower-pitch propeller for specific high-elevation locations.

In some cases, a gear ratio change to more reduction is possible and very beneficial. However, this fix is only safe while the power level is reduced. If the engine is again run at a lower altitude, the gear ratio change must be reversed to prevent excessive torque on drive train parts.

It is a fact that weather conditions exert a substantial 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 now established by the International Standards Organization (ISO).

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 two or three miles per hour in some cases. Nothing will regain this speed for the boater, but the coming of cool, dry weather.

See the thing is it runs bad one time and then good the next. We planned on switching to a portable tank with a short hose and see if that made a difference last time but it worked just fine. The boat is 4 years old and if I had any reservations about restrictions in the hose I would look into that (although thinking about it I know sometimes hose gets mfg wrong....so good point in checking that)

This particular motor is the one that is a 60 hp head unit with a 70 horse sized lower/prop. That being said, I understand that being a sap on power but we're talking about at least a 50% power decrease minimum (if it were a power decrease per-se).

It is also slightly intermittent when it does it, which is most curious. I can periodically get it to spin up a little more than 3200 but it is not consistent. It also, again, is not specifically at elevation... just most consistently at elevation.

I have seen some talk about the VSP filters, which i find curious, but I don't think that would be the issue. I figure if a filter is going to plug, in most cases it would stay plugged.... that and we have gone above and beyond in order to keep good, clean fuel in it.

I'll check on getting the fuel vacuum reading and let you know as soon as I can.

Thanks for all of the help guys!