1994 150hp 2-cycle wont go over 2,200 rpms after it warms up

[FLBoatGuy]

boat a new boat, well new to me... And well i got problems right off the bat.

It's a 1994 150hp 2-cycle.
So the issue is that when the boat warms up, about 15-20 minutes into running it, an alarm goes off under the dash and when that happens the engine will not get above 2200-2400 rpms and shakes pretty bad, it doesn't die. The first time this happened it was under load in the water, but it also would do it in neutral when i attempted to rev it up that way. It will also do it on bunny ears in the driveway too. Basically as soon as the engine is at operating temperature the alarm goes off and this happens doesn't seem to matter if its under load or not.

I have no gauges to tell me what the alarm could be... The water is spitting out of the engine in a nice steady stream, the oil reservoir on the engine is half full, the spark plugs aren't brand new but pretty damn close. When I took them all out they all appear to have the same amount of carbon build up, not too bad on all of them.
I tried removing the spark plug wires while its running, cant really tell if any of them aren't firing, i cant tell if its dropping rpms when i pull them. (is it very minor on these motors?) but it seems like they would be since when the boot is close to the plug its arching to the top of the spark plug on all the wires.

I don't know any ideas?

[99yam40]

overheating would be my guess as low oil level and over heat are what brings in the alarm and RPM limiting.

did you try to add a little oil to the tank to see if that made a difference. needs to be higher than 1/2.

water pump, PRV, and stats should be the 1st thing to look at for overheat

[Jason2tpa]

If this was low oil related it would alarm immediately after the key is turned ON (main tank is not being filled by reserve tank).

My guess:

warm engine + alarm when engine reaches op temp + rpm reduction = high temp alarm

Considering these 3 factors, yeah I agree with 99yam. Your troubleshooting should begin with the cooling system. Sounds like the water pump is operating good, but this doesn't mean water is being pumped through the engine's water passages.

Since this is an older engine, and you're not the original owner, who knows how well maintained it was. With that said, what I'd do first in this scenario is pull the stats and heat test them. If good, then I'd open the head covers to eyeball the state of corrosion. It won't cost you a dime. No point in dumping money into parts if passages aren't free and clear of corrosion.

[FLBoatGuy]

pardon me not knowing but what are the "stats"and how do you heat test them?

Thank you for your input, I really appreciate it, I will definitely start on the cooling system now....

Before ya'all responded yesterday I ran a compression check on all the cylinders and they all came back at 120, so I'm thinking I'm not looking at too major of an issue here.

I also filled the oil tank on the engine, it was roughly 1/3rd from the bottom.
(I haven't ran it again yet, since that)

I pulled the PRV (Pressure Relief Valve)and it seemed fine not really much corrosion in there.

Is there a thermostat on this engine also or is the PRV there instead?

Pulling the heads I'll need a gasket set, so before that is there any kinda engine flush you'd suggest or just better off pulling the heads?



I was also searching for model name/ number on the engine last night so i can order a service manual for it, any suggestions on where to go for one?

Model# on the midsection: 200TLRP
Code: 6G6 L
Serial #: 404 623

looking up those numbers it gives me a 200hp Power Tilt/Trim, Electric Start, 20" shaft - 1991 engine. But the guy I bought it from told me he replaced the midsection a few years back (from the research I've done online the only place with this stamp/plate is on the midsection?) and judging that the engine cover says Yamaha 150 I'd believe it is a 150hp with a 200hp's midsection. I would also tend to believe that it is not a 1994 powerhead like I was originally told but a 1991 since the hull is a 1991 as well, seems to make sense to me.

[pstephens46]

Thermostats. They are closed when cold and open at a particular temp. Say around 140 degrees. I use a kitchen thermometer and a pot of water. I hold the thermostat with a pair of tongs in the water as it heats up. Hold as to not block the top of thermostat. You should see it open between 140-155 degrees.
It should open fully and then retract when it is removed from water.

If they look corroded when you remove, just replace them. You should have two.....$22 bucks each. buy the gaskets too.

[99yam40]

Stat is short for thermostat
each head should have one on the top .

ID sticker/plate should be on clamp brackets

if someone has been putting parts from other motors on it, there is no telling what you have.

no telling what motor that boat had on it originally or what was put on later

I would test oil level and over heat to make sure they funtion.
get gauges so you know what is happening when the alarm sounds

[Jason2tpa]

I also filled the oil tank on the engine, it was roughly 1/3rd from the bottom.

The engine main oil tank has 2 level lines. During normal operation the level of oil will remain in between these two lines. Oil used from the main tank is replaced by the reserve oil tank via the oil pump. If for whatever reason the main tank's oil level falls below the lower level line, the low oil alarm will activate.

Pulling the heads I'll need a gasket set, so before that is there any kinda engine flush you'd suggest or just better off pulling the heads?

You can try flushing with Salt-X, or likewise product. However, if the corrosion build up within the passages are rock solid it won't do much good. Plus you'll only be able to run the engine for the time it takes to warm up before it begins to alarm.

I was also searching for model name/ number on the engine last night so i can order a service manual for it, any suggestions on where to go for one?

Who could say which manual to order until you know for certain the model and year of the engine ('91 or '94), as well as the lower unit. Sounds like your motor has been pieced together using parts from different models and different years.

[FLBoatGuy]

ok so it's definitely an overheating problem not oil. Checked the oil pump and it's all good.

I replaced the thermostats, the "starboard" side's thermostat was not bad but i still replaced it. The 'port" side had a lot of corrosion and about a 1/2 golfball size chunk of salt sitting behind it, replaced that one too after cleaning all the gunk out. (I did check the stats in boiling water and they did both open however...) either way there's new ones in there now.

Then I ran some salt away stuff through it with the whole thing sitting in a big tub and ran it for about 15-20 minutes, the telltale stay relatively cool the whole time. Seemed good, but when I put some bunny ears on and was just flushing it with clean water it sounded the alarm again at about 5 minutes.

I discovered that the temperature sending unit on the starboard side is the culprit for triggering the alarm, when i just tried unplugging it it turned it off and likewise turned it back on when i plugged it back in. It's a bit strange as that side of the enginer was alot cleaner than the port side.

So I don't know, what should I do next? Should I pull the heads so i can really get in there or is there something else I could do before that?

Also out of curiosity the two hole at the back of the engine, these are for exhaust right? Water isnt supposed to come out of them also? (because its not)
One of the attachments I uploaded is a picture of these holes...

And one last thing there's some sorta oilk or grease leaking down the side of the midsection. Now im not sure if it's just flushing some crap out from the top of the powerhead or if this is yet another concern. It's a milking brownish color... I uploaded a picture of that too.

I appreciate all of ya alls help!!!

[Jason2tpa]

ok so it's definitely an overheating problem not oil. Checked the oil pump and it's all good.

I replaced the thermostats, the "starboard" side's thermostat was not bad but i still replaced it. The 'port" side had a lot of corrosion and about a 1/2 golfball size chunk of salt sitting behind it,replaced that one too after cleaning all the gunk out. (I did check the stats in boiling water and they did both open however...) either way there's new ones in there now.

Then I ran some salt away stuff through it with the whole thing sitting in a big tub and ran it for about 15-20 minutes, the telltale stay relatively cool the whole time. Seemed good, but when I put some bunny ears on and was just flushing it with clean water it sounded the alarm again at about 5 minutes.

I discovered that the temperature sending unit on the starboard side is the culprit for triggering the alarm, when i just tried unplugging it it turned it off and likewise turned it back on when i plugged it back in. It's a bit strange as that side of the enginer was alot cleaner than the port side.

So I don't know, what should I do next? Should I pull the heads so i can really get in there or is there something else I could do before that?

Also out of curiosity the two hole at the back of the engine, these are for exhaust right? Water isnt supposed to come out of them also? (because its not)
One of the attachments I uploaded is a picture of these holes...

And one last thing there's some sorta oilk or grease leaking down the side of the midsection. Now im not sure if it's just flushing some crap out from the top of the powerhead or if this is yet another concern. It's a milking brownish color... I uploaded a picture of that too.

I appreciate all of ya alls help!!!

The corrosion you've discovered in the stats is a good indication of whats occured around the powerhead. I'd most definitely pull the head covers. The cost to replace the 2 gaskets for each head isn't too bad, maybe $40-60. Careful unlocking the head bolts, you'd prefer to not snap one. You'll need a torque wrench to reassemble.

Those 2 holes are exhaust ports. Water does not flow through these, however, depending on the air temp you'll see condensation blow out.

The oil stains on the mid section could be coming from the lower cowling pan. If you've got a thick layer of oil lining the cowling surface, when the engine heats up it loosens the oil. Then the oil seeps down out of the lower cowling and onto the mid section. If this is what you discover, a safe solvent to clean the pan is Simple Green. Or any degreaser I suppose.

[scofflaw]

You make no mention of replacing the water pump on this new to you boat. That's the first thing I do on a new acquisition. Don't care how good the piss stream looks

Check both head temps with an IR gun, may be a bad heat sensor on that bank.

I have had good luck flushing with pool acid. I would pull heads as a last resort, seeing chances a high some bolts will break

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