Alarm goes off and idles down over 4k RPMs

[Dalton F.]

its a 97 Yami, 90hp, 3cyl, 2stroke on a 17ft sailfish bay boat.

it starts up fine, idles fine, accelerates fine, pumps water fine, but if i run it over 4k rpms for more than a few seconds an alarm goes off and the engine idles down (alarm stays on). i shut the engine off, fire it back up (alarm is off now), i get back on a plane and continue on my way.

when the alarm goes off the engine continues to pump water perfect.

Other than not running over 4k RPMs its a great motor! i am stumped and any help yall could through my way would be great!



could a problem be my max RPM is at 4500? (Prop is a pitch or two to high)

 

[99yam40]

Re: Alarm goes off and idles down over 4k RPMs

over propped is not good on a motor, and you need to find out if it is overheat or oil alarm

 

[Dalton F.]

Re: Alarm goes off and idles down over 4k RPMs

it has no oil tank...sadly i must mix in the tank.

but how can it be overheating...i kept it around 3.8k RPMs for all of today, witch added up to be about 2hrs of driving and it never heated up and set the alarm off.

 

[Dalton F.]

Re: Alarm goes off and idles down over 4k RPMs

anyone elts have any ideas?

im almost sure it the heat alarm...but why go off over 4k RPMs and not when i run at 3800rpms all day?

 

[Doernuth]

Re: Alarm goes off and idles down over 4k RPMs

You indicated max rpm of 4500. Is that what you get? Or is that the rating? If the engine is only rated for 4k going over could trip a rev limiter of some type and set off the alarm.

Do you have a temp guage? What does it do over 4k?

 

[Dalton F.]

Re: Alarm goes off and idles down over 4k RPMs

The engine will only do about 4.5k rpms then it maxs out. i would think this engine would have a WOT around 5.5k rpms or so...thats why i think im running a prop with to much pitch. but idk what my WOT is for this engine it dosent say on the side of the motor or under the callen.

but i dont have a water temp. but like i said i can run all day under 4k rpms but once i go 4krpms or higher (till i hit 4.5krpms) the engine will run there for about 15-30 seconds then it will sound the alarm. after the alarm sounds the engine idles its self down. i turn the engine off really quick start it back up and go on my way with no sound of the alarm untill i hit 4k rpms again.

but if i never go up to 4k rpms i wont have the buzzer go off. and the engine pumps water fine.

 

[Mr_engineer]

Re: Alarm goes off and idles down over 4k RPMs

You may have a water flow problem thru the head water jackets. I had a similar problem with my 1998 C150 last year. The problem was the water jacket had become clogged with silt and salt buildup eventhough the engine has always been flushed after each use. Removing the head covers, heads and mechanically cleaning them solved the problem. If you use the motor in salt or sandy/silt water, the buildup can occur after several years.

 

[Dalton F.]

Re: Alarm goes off and idles down over 4k RPMs

removing the head covers is this a easy thing to do? i know alot about engines just not really good at putting stuff back together and such...

 

[Mr_engineer]

Re: Alarm goes off and idles down over 4k RPMs

Removing the covers and the heads is not difficult, but it does require some mechanical knowledge, planning, materials and the correct tools such as head gaskets, torque wrenches, etc. If you aren't comfortable with this I wouldn't tackle the project. Purchase a repair manual for the motor, they generally provide teardown and rebuild instructions.

Good luck.

 

[EricJRW]

Re: Alarm goes off and idles down over 4k RPMs

Regarding heat, I'm going to chime in on something I read about, but have never seen. Apparently there are these "heat sticks" that look similar to a lumber crayon. The supposedly come in different temperatures, so you buy the right temp, smudge it onto your motor, and if the temp is exceeded, the mark changes color. If such a thing still exists, it might help.

Of course after typing all that I realize these contactless digital temperature probes are getting pretty inexpensive and are more useful than a lumber crayon... Might also help with getting temp readings on the head.

If this makes no sense, just smack me on the wrist.