80hp Yamaha out of Control

[fishfun83]

I just went out to my boat and started my 1996 80hp Yamaha outboard. Ran a little rough since it hadn't been cranked for 6 months or so but that is normal. After a few minutes of running rough, the throttle started increasing so I shutt the engine off at the switch. Checked the linkage to the three carburetors and all appeared to be normal. Restarted the engine and again, on its own, the throttle increased until the engine was running near red line. I turned the ignition key off and pulled the kill switch but it continued to run at full throttle. I then pulled the gas and after about what seemed to be an eternity, the engine finally ran out of fuel and died. I have no idea what-so-ever what could be the issue. Pulled the carburetor air filter and things looked normal. Check the linkages again and everything looked like they were working normally.

Can anyone offer a suggestion as to what the issue can be? I just retired and was trying to get my boat running to do a little fishing, but looks like that is going to be delayed somewhat. Thanks in advance.

[catmandon't]

Floats?

One or more of your floats must be stuck open.

[catmandon't]

Prime start

Another thought. If you have a prime start system the solenoid may be stuck which woud give you a continuous flow of fuel. There would ba a little red lever beside the centre carb which has 3 positions. Left is normal, centre is continuous fuel and right is off. If the switch was in the middle position turn it to the left and you should be good. If it is to the left yur solenoid may be stuck.

[fishfun83]

Thanks for the information. I am going to check it out tomorrow morning. Really appreciate the help.

[99yam40]

I really do not think the motor will rev up like that unless there is air and fuel increasing going into the motor. You have to have some kind of problem with the carb linkage allowing the ****erflies to open

[rodbolt17]

ok
lets back WAY up.
what does it take to make a 2 stroke articulated rod carburated engine run?
1, intake of the CORRECT amount of fuel to air,
2 compression.
3 spark at the CORRECT time.
4 exhaust.
we cant do anything with exhaust nor compression on that engine.
its a fixed mechanical thing.
what we can do is control the air,thus the fuel with it, and the ign Timing.
dont advance timing and it simply wont go but so fast.
however its amazing how fast it can go with no advance and no load.
for anymore I must have a model number to ID the fuel and ign system I am disscussing.
unlike a lot of others I detest being wrong and the easiest way to not be wrong is to know what I am talking about BEFORE a type.

[fishfun83]

The model number of the engine is C80TLRV

[catmandon't]

No prime start

That model does not appear to have prime start. I have had a runaway motor due to a flooded float.

[rodbolt17]

your words, 1996 80 hp.
your model,c80tlrv.
your engine, c,commercial,80, 80 hp.
t trim and tilt.l is 20" SHAFT
R is remote control and V is 1997.
it is a prime start model.
the odds of a stuck float causing a runaway are slim to none as that would cause 1 out of 3 cylinders to flood and not fire.
to increase RPM you have to have aditional air AND fuel.
cant have one OR the other MUST have BOTH.
thats why I like model numbers, it allows positive ID before I type much.

[fishfun83]

So Rodbolt17, what do you think the problem is? I am confused why I couldn't turn the engine off at the ignition switch. My present thinking there is there must be a non-continuity between the ignition switch kill wire and the engine. I am presently trying to find the electrical schematic to see what wire to follow. I think it is a black one from the ignition switch but not positive. Observations this morning are:
1.Choke was open on all three carburetors
2.Throttle plates were closed.
3. All linkages appear to be working correctly
4. Nothing is binding
5. Everything is operating smoothly.

[fishfun83]

Little bit of an update.
Started the engine this morning and turned it off at ignition OK.
Didn't run out of control but I didn't let it run very long either.
With the emergency wedge pulled, it would not start.
I see no corrosion at electrical connections to motor.

[rodbolt17]

my manual says it is a primestart model.
I will try to look at the parts manual at work tomorrow.
black at the keywsitch is engine ground, white from the switch to the ECU is ign kill.
the key simply shorts the white and black together for ign shut off.
for engine runaway you have to have air and fuel and about 8* BTDC ign timing.

[robert graham]

Seems to me that for the engine to run away,something would have to open the carb ****erflys? Are the carb linkeages operating freely? This is a curious problem and sounds like it could over-rev and damage the motor in a hurry. Good luck and please keep us posted with what you find out!

[catmandon't]

Chokes?

Hmmm, you have chokes. Hmmm, the parts blow up of this site shows no prime start.
Rodbolt quote; "however its amazing how fast it can go with no advance and no load."
Let's assume your switch does work. How then can an engine run on and get fuel. A lot of posters talk of carbon build up in their engines. There are two ways to ignite fuel aside from spark, compression or glowing carbon. That's right, you may have created a little diesel engine for a spell. Maybe the carbon has burned away and this will never repeat. Maybe a float was slightly stuck and now free.

[fishfun83]

I don't think it was glowing carbon as I had only run the engine for a few minutes before it started to run away. I am still baffled as to why I could shut the engine off at the switch or the kill switch yesterday but could not during the run-away 2 days ago. Kinda scary thinking I could have the engine go full throttle while I am alone in the boat in a canal. Not sure what I would do.