1998 yamaha 150's alarms sound at 4200 plus rpm's

[thejman1967]

I bought a boat that was sitting for 1.5 years and needed major clean up. it came with a pair of very clean Yamaha 150's
PROBLEM; both engines sound w alarms at same time running 4200/4500 rpms. when they sound I back off and idle then they shut off???
repairs made with factory parts....
replace and clean new thermostats. complete water pump with housing, pulled heads and cleaned waterways, pulled and cleaned pop it valves, pulled power heads and cleaned mid section (all above looked good with no evidence of wear) flushed entire waterways out while engines were on motor stands and perfect flow w zero restriction.
any other thoughts????????????????? thx jman

 

[99yam40]

Re: 1998 yamaha 150's alarms sound at 4200 plus rpm's

not sure what w alarm is.
what did the gauges say the alarm was?
are positive it is not an oil level alarm?
If one goes into alarm both motors should go into reduced RPMs and sound alarms but should not shut off.

Does the alarms reduce RPM?

 

[thejman1967]

Re: 1998 yamaha 150's alarms sound at 4200 plus rpm's

the W is short for with (sorry)
the alarms sound together and engines both begin to slow down. the alarm is a continuous horn that will stop when I bring to a idle and shut off and restart after a moment. we have dissected the entire cooling system and nothing seems to change. the boat was park and was not able to test prior to buying so I have no idea of there history. thanks for your help jman

 

[99yam40]

Re: 1998 yamaha 150's alarms sound at 4200 plus rpm's

only alarms I have heard about on Yamaha motors are
low oil level in tank on motor(should indicate oil on gauges)
high temp on motor(should indicate oil on gauges)
low voltage ( just some motors and will not indicate on gauges)
water in fuel filter on motor( just motors with that option, and will not indicate on gauges)

This is why I asked what the gauges indicate when alarm sounds

You did not say the RPM dropped before you cut back on throttle before.

So you need to look at gauges and test the systems to see what is working and what is not
That should narrow things down some
Like I said before on duel motor set ups when one goes in to alarm both will so you will have to find a way to figure out which motor is causing the problem