Vibration and power loss at high rpm 1996 30 Yamaha 2-stroke 3 cylinders

[apn3a]

hello i recently started having an issue with my outboard motor. It operates fine for a good amount of time and all of a sudden in high rpms (3/4 to 4/4) it starts vibrating and there is a power loss. It runs fine at 1/4 and 1/2 with no vibration and power loss. In the past, when the vibration and power loss was happening, I knew that the oil tank was low so i would just fill it up and everything would be fine. Now the oil tank is full but it does it anyway. Does anyone have any ideas as of what could be causing this? It does not happen as soon as i start the motor. It happens after about 30min when i go on high rpms.

thanks

 

[mthieme]

Re: Vibration and power loss at high rpm 1996 30 Yamaha 2-stroke 3 cylinders

Does it vibrate in neutral?
If so you can rule out the drive train and it is something in the powerhead.
Are their any noises that you can discern?
The only time I have experienced a vibration was from a bent prop. I assume you've checked this (?).

 

[apn3a]

Re: Vibration and power loss at high rpm 1996 30 Yamaha 2-stroke 3 cylinders

Does it vibrate in neutral?
If so you can rule out the drive train and it is something in the powerhead.
Are their any noises that you can discern?
The only time I have experienced a vibration was from a bent prop. I assume you've checked this (?).

no it does not vibrate at all at neutral. I already checked the prop, i was sure that that was not the case since it starts vibrating after 15-30 min. There are no other noticeable noises whatsoever. When i reduce the speed, it stops vibrating. I run it for about 5 min at low speed and then i go to high rpm again. But after about 5 min it starts to vibrate again, i have power loss, and i have to cut my speed to 1/2. Any other suggestions? Could it be the oil pump? like it does not provide oil to the engine sufficiently in high rpm?

 

[Yamajoe]

Re: Vibration and power loss at high rpm 1996 30 Yamaha 2-stroke 3 cylinders

You need to check your oil sensor and temp sensor. The motor is shutting down to safe mode to protect itself; the reasons this occurs is if you are running low on oil, the motor is overheating and or it is reviing beyond the recommended WOT rpm.

High temp problems are caused by blocked or restricted water intake (lower unit), water pump, thermostat and heavily corroded or build up in the water passages.

 

[apn3a]

Re: Vibration and power loss at high rpm 1996 30 Yamaha 2-stroke 3 cylinders

You need to check your oil sensor and temp sensor. The motor is shutting down to safe mode to protect itself; the reasons this occurs is if you are running low on oil, the motor is overheating and or it is reviing beyond the recommended WOT rpm.

High temp problems are caused by blocked or restricted water intake (lower unit), water pump, thermostat and heavily corroded or build up in the water passages.

after checking all the sensors it seems that when i disconnect the temperature sensor there is no vibration whatsoever. So that means that either the temp sensor is bad or there is an overheating problem. But i doubt there is overheating since the water coming out of the engine seems to be under high pressure. If there was a problem either with the pump or with the water intake, the water that comes out of the engine should have lower pressure. rite..?

 

[Yamajoe]

Re: Vibration and power loss at high rpm 1996 30 Yamaha 2-stroke 3 cylinders

If you cannot hold the palm of hand on the side or top (be careful of moving parts) of motor for more than 30secs, then you should check and replace the water pump and thermostat; also. The water pressure coming from the pee hole is a fair indication of the state of the pump, but i would not rely on the pressure or lack there of; if the water is hot too touch, then you have a problem with your cooling system. Someone here can give you test procedure for the sensor, but my guess is you need to check and replace the pump and thermostat; don't run the motor without the sensor until you have verified the source of the problem and it is resolved.