Merc 3.0 tuneup - fast idle

[Ripple17]

Hello,
On a 1998 Merc 3.0 - I changed the spark plugs from AC Delco MR43T (came with boat) to MR43LTS (engine spec) also replaced the Distributer cap and rotor.

The boat fired right up and after a brief warmup I pulled the trrottle to neutral idle. Previously the engine idled at 750-800 rpm, now with throttle lever back the rpm is 2200. Is this a good thing and should I just reset the idle adjustment?

 

[achris]

Re: Merc 3.0 tuneup - fast idle

Sounds like the throttle cable has jammed. Remove the throttle cable from the carb and set the idle at 750-800, then (after checking that the cable and controls are working correctly) adjust the barrel on the cable to give a slight preload to the throttle lever...

Chris......

 

[antsmands]

Re: Merc 3.0 tuneup - fast idle

+1 on the stuck throttle cable. After I rebuilt my carb and I over tightened the throttle cable bolt and the boat would not idle down below 2000 unless I pushed down the throttle lever. Finally realized that it was too tight, loosened the bolt, a little lube and problem solved.

Tony D.

 

[Ripple17]

Re: Merc 3.0 tuneup - fast idle

I removed the throttle cable after warming up the engine. I am unable to get the rpm below 1100 without the engine ready to stall.
What is the reasoning for using a shop tach - is it just for greater accuracy or is my dash tach way off? Do I need to have the boat in the water for proper idle setting?

 

[achris]

Re: Merc 3.0 tuneup - fast idle

I removed the throttle cable after warming up the engine. I am unable to get the rpm below 1100 without the engine ready to stall.
What is the reasoning for using a shop tach - is it just for greater accuracy or is my dash tach way off?

Your dash tacho could be way off, without an accurate tacho you'd not know...

Do I need to have the boat in the water for proper idle setting?

Yes... and in forward gear, untethered (not tied to a jetty)....

Chris...........