1999 200HP OX66 surging/cutting out

[rjcamel2355]

Hey folks, I have a 99 model 200HP 3.1L ox66 yamaha outboard, motor has ran awesome for the past 5 years, took it out saturday and if I ease into the throttle and keep it under 1/3 throttle itll run and drive all day. If i try to floor it or push it over that point it'll fall on its face, and if I keep pushing it it'll die. I'm thinking it's a fuel pressure issue. I did all new lift pumps (3) 2 years ago, cleaned the VST and new filters the beginning of this year everything looked good, but I replaced it all anyways.

The only thing that makes me think it's possibly not fuel is: When it surges/tries to cut out, the fuel primer bulb is still relatively firm, squeezing it when it's surging doesn't affect it one way of the other.
The shrader valve on the side of the engine, when pushed while idling sprays fuel like it should (will put a gauge on it to determine PSI)

Another odd thing has started happening which makes me think it could be the stator: The voltage gauge will fluctuate (bounce back and forth within 1-1.5 volt range) from around 12 to 14 volts, when going across the lake it sits at just under 14 volts, but when idlling if I turn on my fish finder it'll start fluttering around. Battery is a few years old, and I'll have that tested, but couldn't see that causing the motor to surge like it is.


Any ideas?

 

[99yam40]

rail pressure while problem shows up should tell if that is the problem
mechanical pumps tend to go bad quicker than you would think sometimes.
I think monitoring pressure into the VST while problem shows up should point to that being a problem if it cannot keep up, but I am not positive on that
voltage reading while problem shows up would also tell if that was a problem.

injectors screens plugging up maybe?

 

[rjcamel2355]

rail pressure while problem shows up should tell if that is the problem
mechanical pumps tend to go bad quicker than you would think sometimes.
I think monitoring pressure into the VST while problem shows up should point to that being a problem if it cannot keep up, but I am not positive on that
voltage reading while problem shows up would also tell if that was a problem.

injectors screens plugging up maybe?

Never cleaned the injectors, planned to a couple years ago, but it was running fine so I didn't want to mess anything up.

Will hook up a fuel pressure gauge next time I take it out to run it, it would rev fine in neutral, but I understand that free revving vs running with a load is entirely different.

I just assumed if it were fuel related, that having someone pump the primer bulb as it was trying to cut out or surge would remedy that. Bulb stayed firm the entire time, even when it was cutting out.

 

[99yam40]

just my thoughts, but even if VST is full, the HP pump screen/filter could cause rail pressure to drop at higher speeds, maybe even pressure regulator might also if not working correctly

 

[rjcamel2355]

just my thoughts, but even if VST is full, the HP pump screen/filter could cause rail pressure to drop at higher speeds, maybe even pressure regulator might also if not working correctly

I was thinking possibly the pressure regulator too, I'll pop the VST open in the next day or so and make sure everything looks clean. I did notice that once or twice when I turned the key to on, I didn't hear the HP pump kick on, but I could have just not been listening close enough.

 

[THE CAPN]

Hey folks, I have a 99 model 200HP 3.1L ox66 yamaha outboard, motor has ran awesome for the past 5 years, took it out saturday and if I ease into the throttle and keep it under 1/3 throttle itll run and drive all day. If i try to floor it or push it over that point it'll fall on its face, and if I keep pushing it it'll die. I'm thinking it's a fuel pressure issue. I did all new lift pumps (3) 2 years ago, cleaned the VST and new filters the beginning of this year everything looked good, but I replaced it all anyways.

The only thing that makes me think it's possibly not fuel is: When it surges/tries to cut out, the fuel primer bulb is still relatively firm, squeezing it when it's surging doesn't affect it one way of the other.
The shrader valve on the side of the engine, when pushed while idling sprays fuel like it should (will put a gauge on it to determine PSI)

Another odd thing has started happening which makes me think it could be the stator: The voltage gauge will fluctuate (bounce back and forth within 1-1.5 volt range) from around 12 to 14 volts, when going across the lake it sits at just under 14 volts, but when idlling if I turn on my fish finder it'll start fluttering around. Battery is a few years old, and I'll have that tested, but couldn't see that causing the motor to surge like it is.


Any ideas?

If it were me I would change out the lift pumps. The are relatively easy and cheap to do. Your symptoms are the same ones I had with one bad pump. I think they are supposed to be replaced every 2-3 years anyway. Please report back with your final repairs.

 

[wetneck]

Check rail pressure
Check for leaking lift pumps