'92 70hp outboard problem

[Kingr427]

I was just gifted a pontoon with a '92 70hp outboard from my grandfather. The boat and motor have been maintained very well over the years, and only has 300 hours on the motor. The boat was not used much in the past few years, but I was told it was recently serviced (water pump, carbs cleaned, new plugs, etc). We put it in the water last week and it ran fine. I did notice that there was a red light over the oil warning symbol on the gauge, but my grandfather told me that was always on.

I took it out again yesterday, and just to be safe I premixed the gas and topped off the oil in the engine, so I could tell if any was actually getting pumped through. The engine ran great initially, but after about 8 miles of riding, the engine went into limp mode (no alarms, red light still on, steady stream coming from the tell-tale). I let it run slowly for a couple minutes, after which it returned to running normally for short period only to go back in to limp mode, again no alarm. I continued in limp mode for around 5 minutes and then the engine just completely shut off, and had to use the *****ing motor to get back to the dock.

When we got back, the oil in the tank appeared to be at the same level I had initially topped it off at. I'm assuming the oil pump is the culprit, but if so shouldn't the engine had shut off earlier? How would I go about checking the alarm to make sure it's working? The horn and radio no longer work, so I have zero confidence in the alarm working either. Oh, and even with the switch off, the red light above the oil warning is always on. Thanks for the help

[boscoe99]

There is no "limp" mode in any Yamaha outboard motor. If a red light is on, if a warning horn is sounding, if the motor is in the RPM reduction mode the motor should be stopped immediately. Or sooner.

I would suggest that you take the boat and motor to a Yamaha dealer and have them inspect the motor, determine the problem and fix same. Assuming that the fix is cost effective.

[Kingr427]

Here is a picture of my style gauge... This gauge doesn’t even appear to be plugged in and has the same red light. Is the red square a low warning light or just background color in the gauge?

[99yam40]

Running a motor with a problem until it dies is not good.

I would take a compression test to see if the cylinders are sealing properly.
need to find out why it went into RPM reduction and why it died and would not start again.
worry about the gauge only if the motor is still good.

looks like those icon on the bottom are for oil level
green for good
yellow for caution
red for danger

[pstephens46]

Checking the alarm? Assuming this motor set up has a kill switch with a safety lanyard, pull the lanyard clip out and try start it. Alarm should sound. Hope you didn’t kill it.

[rejesterd]

There's no sensor feedback that would cause the engine to shut itself down, if that's what you're wondering. Describe what you thought was limp mode. It could be that fuel just stopped flowing.

[Kingr427]

Yeah, I’m wonder (hoping) it was a fuel issue also. I was using a small 6 gal tank instead of the main tank since it was easier to premix in. The tank was still about a third full, but maybe that was too low to be consistent.

[TownsendsFJR1300]

Yeah, I’m wonder (hoping) it was a fuel issue also. I was using a small 6 gal tank instead of the main tank since it was easier to premix in. The tank was still about a third full, but maybe that was too low to be consistent.

Fuel tank air vent clogged??

[rejesterd]

Yeah, I’m wonder (hoping) it was a fuel issue also. I was using a small 6 gal tank instead of the main tank since it was easier to premix in. The tank was still about a third full, but maybe that was too low to be consistent.

I would try loosening the cap on that 6 gallon tank and see how it runs for a short distance in calm water. If it's better, then theres a vent/check valve issue somewhere between the tank and the engine.

[panasonic]

Yeah, I’m wonder (hoping) it was a fuel issue also. I was using a small 6 gal tank instead of the main tank since it was easier to premix in. The tank was still about a third full, but maybe that was too low to be consistent.

First thing you need to do is pull the safety lanyard and try to start the engine. The Warning horn should sound, if it does not then that needs to be fixed first and foremost.
Having only a third of a tank of gas would not have made any different in the way your engine will run. You can pretty much burn every bit of gas out of a portable tank.

Was this portable tank clean and have fresh gas in it?

Please answer the questions and maybe someone hear can help.

Will the engine start now that it has cooled down?


If you think it is going into RPM reduction you can test that...you need a service manual to do so.

[Kingr427]

I got a chance to mess with it some this morning. I confirmed the red square, is just part of the gauge and there is an arrow that points to the corresponding level of oil.

I started the engine with premix again and it was idling a little rough. I noticed one of the plug wires had come loose, so once I snugged that back down it ran much smoother.

i took it out for a quick run and it was running normal even at full throttle. I didn’t have much time so I had to stop there.

i did try to check the alarm, there is a chirp when I turn the key switch on, but with the lanyard removed there was no alarm when I tried to crank it.

Im guessing the fact that it was running on only two cylinders was the reason the rpms dropped? Would that ultimately cause it to shut off?

thanks for all the help!

[rejesterd]

Sure, the loose plug wire could cause the engine to run rough and eventually stall out.

You said the horn doesn't work, right? I'm not sure how that all works, but on my hull, the overheat warning sounds just like my horn.. I always assumed the sensor is just wired into the horn, but I haven't dug too deeply into gauges.

[99yam40]

a 3 cylinder motor should be able run on just 2 ,
But I would not think that would cause the motor to shut down

[Kingr427]

Is the alarm behind the controls or is it underneath the console? I’ve found wiring diagrams, but they don’t show the actual location.

[pstephens46]

Is the alarm behind the controls or is it underneath the console? I’ve found wiring diagrams, but they don’t show the actual location.

Part of key switch assembly.