2001 Mercury 125 HP outboard - won't reach full power

[DaveInFla]

OK. Engine was working fine. I'd get 4,500 - 5,000 rpm no problem whatsoever. Took the four carbs off to rebuild (found a lot of varnish and crud in them). Put the carbs back on (in their original order), and the motor starts and idles fine. However, it won't go above about 3,200 rpm. Compressions are all normal. Checked the carburetor bowls, all have fuel. Re-removed the carbs to check floats. All good. Ran fuel from an external tank (bypassed the main tank, anti-siphon valve and fuel filter). Same result.

Rechecked the timing and timing advance. All good. I'm completely out of ideas! The ONLY change was the rebuilding of the carbs.

Does this engine have an automatic rpm reduction for overheat or loss of oil injection?

Any suggestions?

Thanks.

 

[flyingscott]

Did you do a link and sync.

 

[DaveInFla]

Did you do a link and sync.

Yes

 

[jimmbo]

Well, you need to recheck everything you did, every part you replaced, every adjustment/setting you made.

That's one of those goofy 2+2 motors, did you reinstall the carbs in the correct locations?

 

[flyingscott]

Yes you need a factory manual for that motor to set it up correctly.

 

[DaveInFla]

Well, you need to recheck everything you did, every part you replaced, every adjustment/setting you made.

That's one of those goofy 2+2 motors, did you reinstall the carbs in the correct locations?

I did it at least three times. I marked the carbs with a center punch as I removed them to be sure they went back in their original location. They are.

 

[DaveInFla]

Yes you need a factory manual for that motor to set it up correctly.

Thats what I am using.

I have some experience. I’m not a backyard mechanic. I have an A&P license (aircraft mechanic) so I do kinda know my way around engines. Still, I can’t figure this one out.

 

[flyingscott]

Do you have spark on all 4 cylinders? Did you plumb all the fuel lines correctly? Are any of the plastic linkages broken or cracked? What is good compression?

 

[jimmbo]

Did you make any adjustments to the throttle linkage? What about the throttle cable?

 

[DaveInFla]

Did you make any adjustments to the throttle linkage? What about the throttle cable?

Linkage, no, but I did adjust the cable. I followed the mfg manual, and checked it after. It goes full range. To eliminate the chance it was/is the cable, I disconnected the cable at the engine, and operatedthe linkage manually. It went to the full-throttle stop, but still only got 3,200 rpm.

All four cylinders have spark, and I replaced al the fuel lines, from tank to carb, when I put the carbs back on. I triple checked the fuel line routing, and even disconnected them from the carbs to make sure the fuel pump was pumping to all cylinders.

 

[jimmbo]

In post #3 you said you did a link and sync, which would involve adjusting the linkage. Did you check or adjust anything to do with the timing, Max advance or pickup timing points?

 

[DaveInFla]

In post #3 you said you did a link and sync, which would involve adjusting the linkage. Did you check or adjust anything to do with the timing, Max advance or pickup timing points?

Not if you didn’t mess with the linkage adjustment when it was removed. I didn’t. The linkage went back on exactly as removed. One of the steps to adjusting the linkage is to visually inspect the butterfly valves in their idle and WOT position. They are exactly the same.

The timing was set IAW with manufacturer specs. In fact, I rechecked it with a separate timing light just in case.

im going to pull the carbs off again, and re-re-re-check the floats.

 

[DaveInFla]

Again, does this engine have automatic rpm reduction protection in the event of an overheat and/or loss of oil injection pressure?

my Yamaha had it. The symptoms I am having are EXACTLY like those I would encounter with an overheat on the Yamaha.

 

[jimmbo]

You have verified that all 4 cylinders are getting spark at all throttle settings? 3200 sounds about the rpms expected with one dead cylinder

 

[flyingscott]

No there is no rpm limiter on that motor. You did something wrong now you have to go back and find out what that is. A yamaha low oil warning will limit the motor to 2000 rpms. Another Question did you replace the oil lines? If you did was the motor started with a pre-mix tank attached or straight gas.

 

[Sailormike]

Sorry wrong topic

 

[DaveInFla]

All four are getting spark. All four carbs are getting fuel (bowls are full). I’ve been studying the 2+2 system all weekend. I replaced all the fuel lines from the accelerator (enrichment) pump. I found the #3 and #4 check valves, and soaked them in carb cleaner overnight. I haven’t had time to take it out and run it, yet.

Thanks for all the input. It really is appreciated. I do think I will repower, however. NOT a big fan of this 2+2 system.

 

[DaveInFla]

When I used the external tank, I premixed the fuel. And blocked the oil injection.

 

[DaveInFla]

Ok. Back to work.

Took some time off to do some family stuff, but back on my outboard problem today.

I pulled the thermostat and found this. I know it needs to be replaced, but I’m curious if this could be my problem? Not getting up to full power?

Would/Could it be just a coincidence that my power issues, that are caused by this failed thermostat, appeared just as I rebuilt all the carbs?

I’m replace the thermostat, and replace the water pump and let you know.

Fingers crossed?

 

[leonreno]

Wow, that is bad. But not sure it would stop full power. Is the alarm system working on your motor? If that motor has a poppet valve I would recommend changing it also.