1999 mercury 125hp harsh power delivery

[bill j]

I just purchaced a 1999 merc 125hp on a 18ft proline. I just put in the water today for the first time. I was not sure what to expect as my other boat is a 4cyl IO. As i throttle it up slowly. It speeds up and then takes off like crazy. The power delivery is not linear and smooth. I called the guy who sold it to me and I was told it is a 2-4 motor. runs off 2 carbs then goes to 4. I am a ase master mech. So I did order a manual tonight. Any Ideas on this symptom? To me this doesnt seem right.

 

[CharlieB]

Re: 1999 mercury 125hp harsh power delivery

IO?

A 2 + 2 'Outboard' in-line 4 cyl only has idle circuits on the top two carbs, the lower carbs do not allow enough fuel flow at idle to support combustion.

As the throttle is opened an accelerator pump squirts a small shot into the lower pair of cyls to richen the mixture to begin combustiuon, increased airflow thru the carbs begin flowing fuel and combustion continues.

Throttle linkage adjustment, accelerator pump clearance and ignition timing are a delicate balance referred to as 'link and sych'. The proper proceedure for adjustment is spelled out in the OEM service manual and must be done letter perfect. once completed most owners cannot tell where in the throttle opening the bottom cyls begin firing.