merc 120 carb and rpm questions

W

weightset

Seaman Apprentice
Joined
Sep 12, 2012
Messages
33
Got. My boat running after not running for about a year and a half this is a new to me boat so i never seen it eun before this and i have a few quesrltions. For one engine will not start or idle without a little bit of throttle on and what should be wide open throttle rpm i was getting around 3300rpm. It sounded like alot more than that so it may be my tach as well being its 1970
 
Oshkosh1

Oshkosh1

Ensign
Joined
Jun 8, 2009
Messages
968
Re: merc 120 carb and rpm questions

Most carbed engines will require "a little bit of throttle" to start. You must advance the throttle to wide open, then back, then to about 1/4 to start. Allow it to idle "high" (around 1k) for a minute, then back to neutral. It SHOULD hold around 600-700 RPM...in the water. If your setting it on muffs...set it to around 800 initially, it'll back off once the drive is submerged. Ensure your idle mix screws are properly adjusted once it's running. I assume it's some variant of the Rochester 2bbl.

Your WOT SHOULD be around 4200 or so. You can pick up a hand-held Photo-tach fairly cheap to confirm the accuracy of the tach.
 
W

weightset

Seaman Apprentice
Joined
Sep 12, 2012
Messages
33
Re: merc 120 carb and rpm questions

It only has one adjustment screw on it which idk which it controls low or high
 
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