RPM Too High for Speed

[dschweitzer5]

I have a 2004 VMAX 150hp Yamaha on a Ranger 188 bass boat.

Relationship between speed and rpm is off between 3,500 rpm - 5,500 rpm. Full throttle top speed is usually 55mph-57mph at 5,500 rpm. All of the sudden one day tach was showing 5,500 rpm at 3/4 throttle and 46mph. Engine will continue to rev and speed will continue to increase if more throttle is applied but I am afraid to go over 6,000 rpm. I have since tested another day on the lake and had the same problem.

Speed is GPS speed, trim works fine and is adjusted optimally for given speed, prop is fine. I have checked the prop hub and it is not spinning. Holeshot seems okay. Haven't hit anything recently.

Any ideas? Could something in the lower unit being causing these symptoms? Failing tach? Does the engine have a rev limiter that would stop it from over revving if I applied full throttle?

[markle]

Markle

Were you under the dash ,working near tach?Look at the dip switch settings on the back,make sure they are correct.

[dschweitzer5]

I haven't been working under the dash lately. Settings on tach appear to be correct. Wires and connections look okay. Thinking about replacing tach just to be sure.

[boats.net]

Engine does have a rev limiter, activates at 6200 rpm's. Tach could be bad, sometimes will show higher reading. Scribe a line across prop hub and prop washer, if line stays aligned after running prop hub should be ok. Check under boat and on transom for obstructions in front of outboard that might cause turbulence in water flow to prop.

[dschweitzer5]

I have checked prop hub by scribing a line and it is not spinning. No obstructions in front of prop.

Tach reads fine at idle but seems to be about 1,000 rpm too high at 3,500 rpm and above. Will try to check or replace tach next. Thanks.

[dschweitzer5]

Problem was the tach.

[adamcoles]

i have a 30hp 2 storke evinrude,but anymore than half throttle the engine revs and i loose speed. What could be the trouble??

[boscoe99]

Start a new thread. Provide the complete serial number of the motor and a complete description of the problem. When it happens and when it does not.