1996 Force 120 skyrocketing RPM. scary!

parkjehhyun

Cadet
Joined
Mar 7, 2013
Messages
8
Hi all,

Sorry for the long story, but here is what happened. Any help, advice, or insight is MUCH appreciated!



I took my 1996 bayliner with Force 120 HP out a few days ago and ran into a concerning issue..

After fishing for a few hours near the Long Beach Breakwall, my buddy and I decided to head back in and hauled *****, reaching around 40 MPH. Once we neared the harbor, we tried to slow down to a 5 MPH, but noticed the RPM seemed to be "stuck" at a higher-than-normal amount (can't remember the exact RPM, sorry) and couldn't go lower than around 8-10 MPH.

Concerned we were going too fast for the harbor & creating some wake, I shifted the gear into neutral and shut down the motor to perhaps let it cool down.

After a few minutes, I turned the ignition on and within SECONDS, the RPM shot from zero to MAX. it scared the hell out of us, so I quickly turned off the ignition. Confused and unsure of what to do, I repeated the same procedure multiple times before deciding to remove the fuel line.


After a several ignitions after removing the fuel line, the engine ran out of fuel and wouldn't turn over.
I then reconnected the fuel line, pumped the priming bulb, and the engine turned over normally within a few attempts.



-Prior to hitting the water, I had a brain fart and added gasoline BEFORE adding 2-stroke oil (not sure if this is a huge deal, considering the boat ran fine for hours prior to coming to the harbor). Could this have caused it?
-Did running the engine fast possibly cause some type of over-fueling?
-Any tips on what I could do to prevent and troubleshoot if it were to happen again?


Again, thank you for bearing with the story. Any advice/insight is much appreciated!!
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Re: 1996 Force 120 skyrocketing RPM. scary!

Make sure the throttle linkage on the motor isn't getting stuck or hanging up preventing the butterfly plate in the carburetors from closing all the way.

Uncontrolled over revving in a 2-stroke motor can be caused by too lean of a fuel mixture. I doubt that putting the gas in then adding the oil would have caused a problem, since like you said, the boat ran fine for hours. If you haven't replaced the fuel pump diaphragm recently, might take a look at it and inspect/replace if necessary. Check for vacuum leaks. Check the small vacuum hoses and make sure the gaskets around the carburetor base and carburetor adapter plates are in good shape and bolts are tight not leaking. Might want to check the primer bulb itself. It has a small one-way valve that can go bad. Also check any "quick connect" fuel line fittings if you have a portable fuel tank.

If it over revs again, shut it down and squeeze the primer bulb. If that temporarily fixes it, then you know you have a fuel delivery problem.
 

parkjehhyun

Cadet
Joined
Mar 7, 2013
Messages
8
Re: 1996 Force 120 skyrocketing RPM. scary!

Make sure the throttle linkage on the motor isn't getting stuck or hanging up preventing the butterfly plate in the carburetors from closing all the way.

Uncontrolled over revving in a 2-stroke motor can be caused by too lean of a fuel mixture. I doubt that putting the gas in then adding the oil would have caused a problem, since like you said, the boat ran fine for hours. If you haven't replaced the fuel pump diaphragm recently, might take a look at it and inspect/replace if necessary. Check for vacuum leaks. Check the small vacuum hoses and make sure the gaskets around the carburetor base and carburetor adapter plates are in good shape and bolts are tight not leaking. Might want to check the primer bulb itself. It has a small one-way valve that can go bad. Also check any "quick connect" fuel line fittings if you have a portable fuel tank.

If it over revs again, shut it down and squeeze the primer bulb. If that temporarily fixes it, then you know you have a fuel delivery problem.


Thank you for your insight!


I'll start off with the simple checks, like the primer bulb, carburetor butterfly plate, hoses, and other leaks before looking into bigger maintenance issues. (I'm not proficient with outboard maintenance.. YET :D)
 

foodfisher

Captain
Joined
Feb 18, 2009
Messages
3,756
Re: 1996 Force 120 skyrocketing RPM. scary!

X2 on the sticking carb. linkages. (choke)
 
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