RPM won't go over 4000

[jyohe1612]

I purchased a used Mercury 2002 125EXLPTO motor and I'm having an issue that it will not go over 4000 RPM. Spark and Compression is good, pulled carbs and checked the Reed valves. Ran clean fuel through it and still getting the same results. Anyone have this issue or suggestions on a fix.

 

[JDusza]

Unfortunately, the couple exploded views that I use as reference require a serial number as input. Any chance you can get us that?
I have seen incomplete travel on the ignition advance. Without knowing your configuration I cannot say that this is your problem. It's just an idea. I mention it only because you said you got the engine "used". In my case, someone had replaced the design intent linkage rod which ties the throttle to the advance with something off their garage shelf. That was my "used" engine. lol
J

 

[Chris1956]

What pitch prop and what boat is it on? It could just be overpropped.

 

[jyohe1612]

Unfortunately, the couple exploded views that I use as reference require a serial number as input. Any chance you can get us that?
I have seen incomplete travel on the ignition advance. Without knowing your configuration I cannot say that this is your problem. It's just an idea. I mention it only because you said you got the engine "used". In my case, someone had replaced the design intent linkage rod which ties the throttle to the advance with something off their garage shelf. That was my "used" engine. lol
J

Yes the serial number is 0T552683

 

[jyohe1612]

What pitch prop and what boat is it on? It could just be overpropped.

I have it mounted on a 1997 Starcraft 190 Superfisherman. I will see what the prop is and get back to you. The marina that was working on the motor replaced the prop because he dinged the one up that was on there.

 

[jyohe1612]

Yes the serial number is 0T552683

Here is everything that the mechanic checked out and he ran out of ideas.

 

[jyohe1612]

I have it mounted on a 1997 Starcraft 190 Superfisherman. I will see what the prop is and get back to you. The marina that was working on the motor replaced the prop because he dinged the one up that was on there.

The prop is 13 1/4 x 17

 

[Faztbullet]

Is it stuttering like mechanic stated or runs good but no max RPM?

 

[jyohe1612]

Is it stuttering like mechanic stated or runs good but no max RPM?

It runs really good until it hits the 4000 rpm mark and then it starts to stutter like it's starving for fuel is what the mechanic told me.

 

[Faztbullet]

Disconnect the rectifier and retest...

 

[jyohe1612]

Disconnect the rectifier and retest...

Not sure what you mean here, sorry I’m not good with motors. Are you saying to disconnect this component and then start and run the boat to see if it goes over 4000 rpms?

 

[Faztbullet]

yes....

 

[jyohe1612]

yes....

Thank you I will try that this weekend and let you know how it works out

 

[jyohe1612]

Disconnect the rectifier and retest...

I tried this over the weekend and no change it the performance.

 

[jyohe1612]

I have it mounted on a 1997 Starcraft 190 Superfisherman. I will see what the prop is and get back to you. The marina that was working on the motor replaced the prop because he dinged the one up that was on there.

I changed the prop to the 13 - 3/4" x 15" and didn't notice a difference.

 

[kytooner]

I was going to say try different tank and fuel line but I see he tried that. Might try it again with new hose just in case he didn't try the new hose part.. But reading through his notes he talks about blown gasket and water on the wrong side but doesn't report it repaired. What about that

 

[jyohe1612]

I was going to say try different tank and fuel line but I see he tried that. Might try it again with new hose just in case he didn't try the new hose part.. But reading through his notes he talks about blown gasket and water on the wrong side but doesn't report it repaired. What about that

The blown gasket was repaired.

 

[kytooner]

The blown gasket was repaired.

Outside of new tank and hose, my next easy thought would be spark plug wires (assuming spark plugs have already been changed).

 

[JDusza]

May not be running on all cylinders ... ?
Is it worth trying to pull each spark plug lead while running and see if performance changes? If you pull a wire while running and operation changes, then that cylinder is working. If you pull a wire and nothing happens, then that cylinder is dead.
Would this help? I'm currently arguing with a small Merc that shows bench test spark on a tester and plug but the cylinder function is verified dead when pulling the wire while running.
J