Mercruiser 120hp 2.5 carb settings

[stingray165ss]

Hey guys I have a mercruiser 120 with the Rochester carb on it, could someone please tell me the correct carb needle settings. I am not to familiar with how to tune the carb. Any pointers would be greatly appreciated.

 

[Bt Doctur]

Re: Mercruiser 120hp 2.5 carb settings

You must be a "youngen"
Your looking for the highest idle speed.
From GENTLY SEATED back out about 3-4 turns and start motor. Slowly screw them inward listening to the engine to increase speed.
Adjust to highest speed and then back them out 3/4 of a turn.Re-adjust idle speed with idle speed screw.

 

[stingray165ss]

Re: Mercruiser 120hp 2.5 carb settings

So i will use this method for both screws? do the screws affect on the idle and low rpm's or will they have an affect on the engine at full throttle?

 

[cecho]

Re: Mercruiser 120hp 2.5 carb settings

Turn both screws the same amount 1/2 of a turn at a time until you get close. Make sure you keep both screws the same number of turns in. Turn one by 1/2 then turn the other 1/2. Then fine tune it by ear. Turn one a little in and the other a little in. If the engine gets faster do it again. Once the engine gets a little slower back both out 3/4 of a turn. The screws will only affect the mixture up to around about 1/4 throttle or so. At that point the metering rod then the jets start to take over. I doubt you need to mess with the rods or jets though.