Merc 125 Flat Spot Or What

[zazusa]

Please Help
I Fitted A Merc 125 Outb. On My Boat
On Exele The Motor Runs Week And Then On Aprox 2000-2500 Rpm The Motor Comes Suddenly To Live Is That Normal Or Is Something Wrong.
2nd Problem.
At Power And Planing Stage The Boat Have The Tendancy To Pull To The Right Hand Side. Do I Need To Set The Trim Tab.
Thanx
Zazusa

 

[Laddies]

Re: Merc 125 Flat Spot Or What

Your engine runs on 2 cyls till about the speed your speaking of, you might ck propping as that will make them bog if the prop has to much pitch. As far as steering torque at wot if the wheel pulls, turn the trim tab in the direction the wheel pulls

 

[fpdiver]

Re: Merc 125 Flat Spot Or What

I have the same motor and previous post is dead on. This is a "feature" that allowed the motor to meet some EPA requirements. We run to 2000RPM (6 mps) and we just understand that the next available speed and RPM is 2800 and 15mph. The only time this is an issue is trying to hold 5mph against the tide. There have been times where I have had no choice but to go 10mpg (15mph vs water) in the no wake zone. It was either that or get pushed out sea

 

[CharlieB]

Re: Merc 125 Flat Spot Or What

Sorry, but as an owner of a 2 + 2 and a Marine Machinist/Mechanic, I have to respectfully disagree.

True the 2 + 2 idles only on the top 2 cyl's, the lower 2 carb's do not have an idle circuit.

HOWEVER, they do have the off-idle fuel ports, at least my 1996 does, and the moment that the butterflies are moved off-idle fuel begins to flow and the cyl's begin to fire. They only flow enough fuel for a 'steady-state' burn and are not overly rich as the base idle port is not there and they do require the accelerator pump shot for accelerating the motor to any given RPM/throttle setting.

Base idle RPM 750 - 800 in forward gear, I can throttle to 900, 1000 any setting I need and it just works.

If you are experiencing any flat-spotting, or 'stepping' of RPM then you need to thoroughly clean ALL CARBs, and follow the link and synch directions to the letter.

 

[jsturkie]

Re: Merc 125 Flat Spot Or What

Sorry, but as an owner of a 2 + 2 and a Marine Machinist/Mechanic, I have to respectfully disagree.

True the 2 + 2 idles only on the top 2 cyl's, the lower 2 carb's do not have an idle circuit.

HOWEVER, they do have the off-idle fuel ports, at least my 1996 does, and the moment that the butterflies are moved off-idle fuel begins to flow and the cyl's begin to fire. They only flow enough fuel for a 'steady-state' burn and are not overly rich as the base idle port is not there and they do require the accelerator pump shot for accelerating the motor to any given RPM/throttle setting.

Base idle RPM 750 - 800 in forward gear, I can throttle to 900, 1000 any setting I need and it just works.

If you are experiencing any flat-spotting, or 'stepping' of RPM then you need to thoroughly clean ALL CARBs, and follow the link and synch directions to the letter.

Charlie, I have a '95 125. Just purchaced in March '09. Rebuilt fuel pump/new kit. Rebuilt all carbs w/gasket kits. They were quite clean. Replaced both inline filters, junk was in the Accel. filter. Link-n-sync per Seloc. My motor runs great but I do have a "jump" spot in throttle.

Me being one to do research, you are the second one that I have ran across stating that the 2 + 2 will power up smoothly if everything is adjusted right. I agree, but for the life of me I cannot get my motor to do it. @ 1800-2000 I plow through the water for a second or two then take off. My base idle and RPM are spot on yours. The ONLY thing I have not checked on my motor is the two injectors.

But I guess to sum it all up, my motor idles great, runs at WOT great, so I shouldn't have anything to complain about. I mean, many people on this forum is in alot worse shape than me. Maybe one day I'll dial it in perfect!

 

[fasassvalk]

Re: Merc 125 Flat Spot Or What

Charlie, I have a '95 125. Just purchaced in March '09. Rebuilt fuel pump/new kit. Rebuilt all carbs w/gasket kits. They were quite clean. Replaced both inline filters, junk was in the Accel. filter. Link-n-sync per Seloc. My motor runs great but I do have a "jump" spot in throttle.

Me being one to do research, you are the second one that I have ran across stating that the 2 + 2 will power up smoothly if everything is adjusted right. I agree, but for the life of me I cannot get my motor to do it. @ 1800-2000 I plow through the water for a second or two then take off. My base idle and RPM are spot on yours. The ONLY thing I have not checked on my motor is the two injectors.

But I guess to sum it all up, my motor idles great, runs at WOT great, so I shouldn't have anything to complain about. I mean, many people on this forum is in alot worse shape than me. Maybe one day I'll dial it in perfect!

Same here ! I have a 2000 125 and it idles beautiful runs wot great but does have the 1800-2000 rpm transition (whip lash effect) engine has less than 100 hours carbs good, all sync and good per mercury manual. Never any trash or water in fuel.
Like the previous post , I am happy and can live with it. But I have heard more 2+2 owners say the same than those saying a smooth transition to all four carbs. I dont doubt Charlie word, just wish he could fine tune mine for me!

 

[CharlieB]

Re: Merc 125 Flat Spot Or What

OK, I do have my throttle pick up roller set a little tighter than spec, same with the accel pump gap, it's about half of spec.

 

[fasassvalk]

Re: Merc 125 Flat Spot Or What

Will give that a try Charlie, Thanks for the tip