Pro V losing power

[Truman Kid]

I have a '89 Pro V on a '88 Ranger 390, which has always ran very strong. Recently I noticed that it would run 1-2 minutes at 4500-5000 rpm then dye down to 3500. The other day it would get up on plane, hit @4000 then drop off to 2500 rpm. When I bring it back to idle, then hit it, it goes on plane then drops to about 2500 again. I'm up in Kalispell Mt and Yamaha dealers are few, much less the guys who have worked on older Pro Vs. Am I looking at a fuel pump issue here, or something much worse? I'd appreciate any input.

[rodbolt17]

a complete model number is nessasary.
many engines got labeled pro-v.
was a marketing thing not a model identifier.
did it ever run correctly at that altitude?

[Jason2tpa]

did it ever run correctly at that altitude?

Man, great question rodbolt. Never occurred to me that altitude affects engine performance. I assume because of the thinner air?

[pstephens46]

Yep. The 80 Pinto never did well on the blue ridge parkway.

[cpostis]

Man, great question rodbolt. Never occurred to me that altitude affects engine performance. I assume because of the thinner air?

Truman Kid, you boat in Flathead Lake, MT? If so, Beautiful. see the attached image.

Guys, this lake is about 2,900 feet above sea level. What would you have to do to get best performance at this altitude? Is there a certain altitude where changes become necessary?

[Truman Kid]

Reply

I don't run much on the Flathead, but it is a nice lake. And it did run real strong until the problem. I do believe it is a genuine Pro V. Actually bought it @ Quaker Marine in Eastern PA as new years ago. Since then we migrated west. And the altitude does make a difference, it runs richer , w/ less power than it did on flatland.

[Truman Kid]

Model? serial # for RODBOLT

The tag on the port side of the engine says " PROV 150G" in the serial # area "304073". I hope that helps.

[boscoe99]

Man, great question rodbolt. Never occurred to me that altitude affects engine performance. I assume because of the thinner air?

Yes, thinner air. Thinner air means less oxygen. Less oxygen means less power. Here is a snippet from Mercury Marine that addresses other issues that can result is loss of power.

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.

[boscoe99]

Truman Kid, you boat in Flathead Lake, MT? If so, Beautiful. see the attached image.

Guys, this lake is about 2,900 feet above sea level. What would you have to do to get best performance at this altitude? Is there a certain altitude where changes become necessary?

Rejet the carburetors. Make sure that the propeller is sized so as to let the motor turn at or near its red line RPM when the throttle is wide open with the engine trimmed to the most efficient trim angle. Get rid of any unneeded weight.

[boscoe99]

The tag on the port side of the engine says " PROV 150G" in the serial # area "304073". I hope that helps.

That's almost it. PROV150LG should be the complete model identity. Remember that for future use. The G indicates it is a 1988 model year motor.

http://www.boats.net/parts/search/Ya...0LG/parts.html

304073 is the serial number.