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**rodbolt17** · 06-30-2013, 08:39 AM

if all is working,anytime you get a RPM reduction you also get the audible buzzer and RPM is limited to about 2500 RPM max.

on that engine low oil in the engine tank,overheat or low battery voltage can cause it.
no audibles or limp homes for the remote tank.

on this note.
there is NO "limphome" mode.
RPM reduction is caused by an issue that will most likely destroy your powerhead if it continues to run.
RPM reduction is to alert the operator that a problem has occurred and its time to shut it down and inspect, not continue.

**rhodyboater** · 07-01-2013, 09:14 AM

Thanks rodbolt! followup questions

Thanks Rodbolt. Yes, I slowed right down was back home within 5 minutes when the RPMs dropped. I am new to this engine so I am extra careful and nervous.

I do have a few thoughts, maybe you can comment?

Buzzer: I think there may be two buzzers, one (maybe in the yamaha tach with the green and red lights?) that is just for the oil reservoir. That works. It was green when the limphome went on. And perhaps another buzzer for other issues. I don't think that works. I was doing some rewiring (it was all messed up) in the helm and saw a pink wire to buzzer, but it looked pretty beatup.

I am assumming the limp home is some RPM limiter? I originally thought it worked off by shutting down one or two of the carbs, but that sounds too complex.

Why would the oil buzzer go off when the reservoir is full at startup? It has done this twice and I had just filled it. Maybe some sediment got into the tank sensor?

I think my real issue is related to coolant. I had mistakenly started the engine a week ago in the mud. I ran it a long time after that and all was well. Then this issue happened a few days after. I am thinking some sediment got into the system, settled somewhere. I am thinking the poppet. I had the impeller and thermostat changed this year.

I don't think the issue is fuel or ignition b/c it only dropped in RPMs but ran smoothly. However, does the limphome react to a low oil pressure? That would be my second guess. How does it sense a low pressure ?

I am thinking of changing the poppet and trying it. Is theer a way I can monitor coolent temp, maybe hold my hand in the telltale stream? If it goes into limphome I want to check the sesors on the engine. I am thinking to use a ohmeter and see if the pink wire in the cyliner head goes to ground. Also, is there two temp sensors? one for coolent and another for combustion. I would think not, again too complex.

I thank you for your comments and hope you will help again and answer a few questions.

Thanks
all!

**rhodyboater** · 07-01-2013, 05:15 PM

update

Hello:

Problem still not checked but I did some research and I answered some of my questions (but correct me if I am wrong!):

1) the motor uses a rev limiter when it senses a problem.
2) the buzzer doesn't always sound.
3) I read an older post by rodbolt and the most sensible problems (b/c the motor seems to run OK, no stalling/shuddering) are temperature or the 2cy oil injection.

I also called a mechanic to get the poppet valve. He questioned if the engine was pumping, I said yes and there is a telltale stream, but I don't know if its less powerful then before. He stated that once the revlimiter activates it stays on until the motor is restarted. He suggested I run it again without the cowl and if it the revlimiter activates, pour some water on the head, if it boils it is too hot.

So, I plan on doing two things. Run without cowl. 1)Watch the onmotor oil reservoir. If I see it going low, then there is a problem with the reservoir or reservoir pump. Perhaps gunk got in when I recently filled it. 2) And if the reservoir stays fine and the revlimiter still comes on, pour a little water on the head to see if boils. And maybe see if the sensor is activated by checking to see if it is grounded out.

Let me know if this seems OK and also, can I do this in neutral in the water? I would rather stay close to the dock.

Thanks anyone!

**ausnoelm** · 07-01-2013, 07:51 PM

I don't want to derail this, or anything like that BUT.....I think you should read what rodbolt said very carefully, there is NO "limp home" if the motor has a fault that reduces the RPM, you do NOT limp home, you stop the motor, NOW! and any mechanic that tells you to tip water on the motor to test for temperature needs to have the water tipped on HIS head (in my opinion) that is not a way to check for an over heat.

**rhodyboater** · 07-03-2013, 10:42 AM

Yes! I totally agree, I guess limphome is not the right word. I do take this seriously, I just drive in circles near my dock.

Well, I removed the cowl and saw the sensor on the oil reservoir on the engine was dislodged. I pushed it back in. Buzzer did not sound when I started it up. I drove it awhile in circles around my dock and kept an eye on the reservoir (stayed full) and put my hand on the head a few ties (stayed warm).

But I still have an issue...the engine was not performing as usual. First the tach does not work, so I am going by noise. The engine seems to rev up about only half and the boat just about gets on plane. Engine sounds like its going about 2-3 grand RPM. But runs smooth. GPS says 12 mph. Its a 150 on a 20 footer, it should go about twice that.

So, I talked to a mechanic on the phone. He thinks its the carb high speed jet. He suggested getting it up and pushing the choke in a second to see if it speeds up a bit. Also, check the fuel pump by squeezing the fuel bulb .

I still suspect its in RPM limit mode. I am a car guy and the old line is that 90% of carb problems are actually electrical, but I am realizing that is not for boats.

I am charging the battery to make sure its not low voltage. I just wish there was a way to see if its in revlimiter some other way other than the buzzer, becasue I think the buzzer does not always sound.Once I run with a fully charged battery and its still seems low I will start looking at the fuel system. But any thoughts are appreciated!

M

**99yam40** · 07-03-2013, 01:52 PM

If you buzzer does not sound off each time a condition is met that calls for it you need to fix that.

There are 2 ways to reduce or limit RPM, retard timing or drop spark.
Both are easy to detect with a timing light and spark tester to see what is going on while problem exist

**rodbolt17** · 07-04-2013, 07:14 AM

car guys should NEVER be allowed to remove the hood.

Diesel guys should NEVER be allowed on the boat.

electrical failures on that engine are very rare.
fuel and cooling fairly common on car guys rigs.

**rhodyboater** · 07-06-2013, 08:22 AM

Update

Hello All:

Looks like the thing that is causing the revlimiter to kickin is voltage. A fw days ago, I checked the battery voltage, 12,2 and then drove it, still low on revs and GPS said 12 mph. I charged battery overnight, read 13.4 volts and boat the ran good, up to 20 mph. I drove it again today, ran good, but the second I hit the tilt button (power draw) the revlimiter kicked in.

I have always known that the rectifier was bad. But my mechanic said not to worry once the engine starts it runs on its own magneto. However, I think he forgot the computer doesn't. And there is the oil pump and other accessories drawing power. When you get up in RPMs the engine does draw current and if the engine is not charging it doesn't seem to take much to kick in the revlimiter.

So, I guess a rectifier is in my near future. Just curious, does anyone know the voltage the revlimiter kicks in at? Would seem to be sensitive, I would say below 11 volts. My battery is only a year old.

Please comment. I like any input!

Rodbolt, thanks, you posted awhile ago that revlimiter causes could be temperature, oil and voltage. I just went down your list.

M

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limp home cause? 1990 150 HP yamaha

limp home cause? 1990 150 HP yamaha

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