50 2 stoke Yamaha going into limp mode with no alarm?

[islander9]

Hello, I am hoping to get some suggestions on how to diagnose why my 2000 50 hp would go into what seems like limp mode. It will run fine at <1500 rpm and shut down at any rpm above. Have tested the alarm and it works when temp sensor wires are bypassed and connected together.Have replaced the impeller and it I am quite sure it isn't running hot. Oil tank is full.
Have opened up all the wiring connectors to check for clean/corrosion.

Can a CDI failure cause the engine to go into limp mode with no alarms? Any suggestions on what to look for?

Thanks

 

[99yam40]

\would go into what seems like limp mode. It will run fine at <1500 rpm and shut down at any rpm above.

what makes you think limp mode will shutdown a motor?
It will not, just limits RPM to about 2000

You need to find out is it is running out of fuel or spark is going away if it is shutting down

 

[islander9]

The engine is new to me and had been sitting for 2 years. I am fairly experienced at OMC and Merc engines, but very little time on Yamaha's.

I have soaked the carbs and installed new needles and seats.
I knew the engine had this problem when I bought it from the previous owner so I spent considerable time checking oil and fuel lines and electrical connectors, rub through's, when I had it apart cleaning the carbs.

I was testing it today and noticed it runs fine for about 15 minutes and then the rpm's start to drop off about 100 rpm at a time until it won't run any higher than approx 1500 rpm. Today I also disconnected the wire coming from the oil tank to the pink wire that feeds the alarm, although I am not getting an alarm.

If I let the engine sit for a couple of hours it will repeat the issue as described. Once warmed up it won't go above 1500 rpm with both temp and oil sensors disconnected.

Any suggestions would be appreciated.

 

[schematic]

check the diaphram pump for fuel leaking into crankcase. rupture diaphram or cracked pump housing....

 

[islander9]

Thanks I will check it today. If it is leaking back into the crankcase would I expect to find fuel in the pulse port of the pump and at the case? My fuel ball stays hard and the engine idles great before the issue overcomes the engine, after the issue hits even the idle is effected somewhat.

 

[islander9]

Thanks I will check it today. If it is leaking back into the crankcase would I expect to find fuel in the pulse port of the pump and at the case? My fuel ball stays hard and the engine idles great before the issue overcomes the engine, after the issue hits even the idle is effected somewhat.

 

[99yam40]

That motor should have the prime start system on it.
Make sure it is in the normal position.
have you tested to see if the alarm system works properly?
That would tell you if the oil or over temperature switches cause the RPM limit.

By the way do you have a tach with the lights to indicate what alarm comes in when the buzzer sounds and give an accurate reading on RPM?

RPM is reduced during safe mode by timing being retarded, so it is easy to check timing with a timing light to see if that is happening.

Maybe your fuel pump is not pumping enough fuel to keep running due to restrictions or sucking air.

There are some good testing procedures in the frequently ask questions section of this forum. if you cannot find it let me know and I will help.

 

[islander9]

Hi there, yes it does have the prime start on it and I checked it while I was cleaning the carbs. I have also confirmed that the manual toggle is in the right position. I have also confirmed the alarm is working by disconnecting the over temp sender and connecting together the feed wires to it.

I have a tack that shows trim level, oil alert and overtemp. It is not one of the models that has any buttons on it to select other functions (can't find the model tack to quote it). It is showing me an idle speed of 700 rpm and shows 5200 rpm at WOT, which is what I was expecting so I haven't questioned the accuracy. I am not getting any alarms or error indicators on the tack when it fails?

I had the fuel lines off the pump today and they are all soft and seem to be well sealed. While I don't have much experience with Yamaha outboards, I can surly recognize fuel starvation on a Merc, or an OMC and it doesn't fall from full power quickly like I have seen on them. It takes about 30 seconds for it to drop 100 rpm at a time from 5000 rpm to about 1500. Once in failure it will stay that way until the engine completely cools, usually overnight. The next day it will work well for about 10 minutes and fail again.

I will take it out after dark with a timing light to see if it retards the timing while it is failing. I also have a 7psi electric fuel pump that I use for testing that I will also use to supply the fuel to rule out my pump as a problem.

Off to the FAQ to see what else is there.

Thanks everyone for the help so far!

 

[99yam40]

no need to wait till dark.
Mark the timing position with white paint or chalk, the timing light should be bright enough to see.

If you move the timing light to the different plug wires you can see if they are getting spark.
But my guess is a fuel problem

I take that back if you have to let it cool off it may be spark issue, but easy to test for

 

[islander9]

First off, a big thanks for all the help getting me through this so far! Oh so simple and yet when it eludes you it can seem so complex.

For the first time today I am hearing a lean sneeze at cold idle and sometimes it will even stall, it is good after it is warmed up. Earlier this week I soaked the carbs in a real good product, replaced the needles and seats and blew them out as I have done 100's of times, so I am going to assume it isn't the carb's for now.
Hooking up the electric fuel pump was not going to happen so I'll rebuild the fuel pump on spec just for peace of mind.

Tried as I might with a white grease pencil filling in the timing marks, I wasn't able to see the timing marks in the bright sun. So I'll give it a go after dark, Am in the ball park looking for 4 degrees at idle and 27 at full advance?

I was able to confirm that I have spark on all 3 cyl's when it is in failure, so I guess some progress has been made.

Thanks again.

 

[99yam40]

service manual for your motor wll give all specs and procedures, it is a must when working on it.
my guess is 7 to 25, but 4 to 27 could be correct. need to look it up in your service manual

What position do you have the prime start in?

testing fuel pump pressure/ vacuum might say if pump is good, but will not say if leaking
Does pumping primer bulb make a difference?

 

[islander9]

Completely agree the manual is vital, I have one coming mid week. Thanks I'll look for approx 4-27.

The prime start is in the auto position. The primer ball is staying hard and trying to force more fuel through it has no effect.
I picked up a fuel pump kit yesterday on spec.

New little symptoms I am noticing which may support a bad fuel pump is a slight lean sneeze at idle and a large plume of exhaust when starting after sitting for a few minutes.

 

[99yam40]

cylinders need good compression, good spark at the correct time, and the proper fuel to air ratio to fire properly.
fuel is not easy to test but everything else is.

If fuel pump was a problem and not pumping fuel enough to fill the bowls then using the primer bulb would help,
so that can be eliminated unless it is leaking into the crank case and that would flood #3 cylinder.
Did you see the testing fuel system in FAQ, simple to do.

Did you check to see if timing was doing its thing when problem shows up?

 

[islander9]

Update that it is fixed and a big thanks to everyone!!

It turned out to be the fuel pump leaking back into the pulse port. In hind sight I should have clued in that the experienced folk's here were pointing at the pump from the beginning and sometimes the experience we (I), have can lead you astray. I never did find testing the fuel pump in the FAQ, but now I am determined to find it.

Appreciate everyone's time and effort!!

 

[GA_Boater]

There is no FAQ for Yammies in the stickies.. Does the manual you just got have fuel pump testing?

 

[99yam40]

http://forums.iboats.com/forum/engi.../290505-how-to-testing-your-boats-fuel-system

This should work for any fuel system

 

[robert graham]

Every 5 or 10 years it's not a bad idea to just replace that fuel pump with a new one.....Hopefully before it fails....if your old pump is/was still working O.K. then keep it for a spare. Fuel Pumps, water pumps, tires, batteries, etc.....all better to replace Before they fail!.....

 

[JRock80]

I have a different issue, hoping someone can give me some insight. I was leaving Canal I must have picked up a plastic bag. When I got to the bay I throttled up when I got to 2500 RPMs the outboard started to shake and would not go any higher. When I stopped the boat to check to make sure I didn’t snag a crab pot line, when I raised up the motor, next to my boat was plastic bag. The outboard was overheating due to limited water intake. The water pump seems to be working but the engine is stuck in Limp Mode. Thoughts on how to fix it? I assume I should replace the water pump either way, possible the sensors? The Outboards is a 2005 Johnson 90 2 stroke.

 

[99yam40]

why are you posting on an old Yamaha thread about a none Yamaha motor?

 

[GA_Boater]

why are you posting on an old Yamaha thread about a none Yamaha motor?

Good question, 99.

JRock80 Please start a new in thread in the Johnson/Evinrude section.

Closed.