40 mercury high idle

Maxlamb85

Recruit
Joined
Mar 25, 2013
Messages
5
82 40 hp mercury hard to get started and idles super high when it does start. Ran fine 2 weeks ago on trailer. Problems started today. Boat hasn't been in the water since weir was bought and nothing has been messed with as far as carb timing etc. how hard is it to do the timing?
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Re: 40 mercury high idle

Could be a partially blocked carb and its running lean. When they run lean they increase their revs and overheat very quickly, sometimes even a thermal runaway will happen if run in that state on muffs and that can be game over and dangerous.

How many carbs do you have on yours. If more than one Have a look at your plugs to see if they look even
 

Maxlamb85

Recruit
Joined
Mar 25, 2013
Messages
5
Re: 40 mercury high idle

It just has one carb. 2 cylinder engine. I pulled the plugs and they looked fine a little dirty but nothing too bad. Also the plugs are flat with no piece coming off the top for like the gap or whatever like a normal spark plug. Never seen those before. My first thought was a carb problem but after a lil research i started thinking about the timing. I guess a carb clean/rebuild is where we should go next?
 

Georgesalmon

Lieutenant Commander
Joined
Apr 14, 2012
Messages
1,793
Re: 40 mercury high idle

First just check that when in neutral the throttle linkage is pushed lightly against the stop and the carb butterfly is closed. Before you start messing with carb settings and timing do the easy checks.
 

Fleetwin

Lieutenant Junior Grade
Joined
Nov 23, 2011
Messages
1,141
Re: 40 mercury high idle

First just check that when in neutral the throttle linkage is pushed lightly against the stop and the carb butterfly is closed. Before you start messing with carb settings and timing do the easy checks.

Agreed. Unhook the throttle cable and make sure the carb butterflies are closed. If they are, you have an air leak somewhere in the carb/intake system.
 

Maxlamb85

Recruit
Joined
Mar 25, 2013
Messages
5
Re: 40 mercury high idle

Thanks for the suggestions. Ill check those things as soon as i get back to my buddys house. Its his boat im trying to get up and running. The thing that gets me is this motor sat for a year. 2 weeks ago it started right up and ran smooth on the trailer. He went and got it registered yesterday and we started on trAiler again before leaving for the water and the high idle problem started. Also if it helps when i sprayed a lil burst of starting fluid in the carb it seemed to slow down the rpms alot.
 
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