2003 25hp bigfoot idle speed

[DagsHuggy]

This year I purchased a 16foot pontoon boat with a 2003 25hp Mercury bigfoot on her. From what the seller said it was his dads who passed away and he doesn't use it much, thus selling it.
The motor runs good the only issue is idling. It seems to run fast in Neutral and putting it in forward or Rev. sounded like it was being hard on clutch. The farther in-law made a small adjustment (turning a small screw) and we ran some seafoam in the gas. The farther in-law was at the cottage this past week and he was telling me that, now it seems to be hit or miss on how it runs on idle it can be run fine one time and the next time you start it she is idling fast or feels like it may stalling out in neutral . It makes it really hard to dock and again hard on the clutch. Is there any ideas on what to look at or anything else to adjust??
- Its never been hard to start
- seem to run fine when boating

- I do wonder if the choke is sticking open as it has one of the key chokes where you push the key in to choke. been wanted to separate that and put a button in just for the choke.

I am not a mechanic I did print out the manual for the motor but I am not finding it helpful.

 

[DagsHuggy]

Bump....

if it helps its 4 stroke....
I may have a chance to look at it this coming weekend, if someone can point me in the right direction... I pick up so more seafoam and may run that in it again... need some help on this one, as hearing the gears when putting it in Forward or Rev is disconcerting and trying to dock a boat that is stalling in Neutral is hard.
Not sure how to clarify this post but, here is a run down.
-Start boat fine
-Seems to run high from the beginning
-Put it in Rev to pull away and hear gears.
-Put in Neutral from Rev and still seems high idling
-Put in Forward from Neutral and hear gears
-Boating at any speed seems fine (no RPM to judge)
-Approach dock and Neutral to coast in seem to want to stall (only sometimes) other times seems to sound like High Idle

We so run high oct fuel in it 91oct not sure if that would make a difference.

Any help??

 

[DagsHuggy]

Can humidity play a roll in how a outboard runs??
could that be an issue?

 

[Chigwalla]

I've run across that problem a few times, mostly in boats that sit.
I start by running the engine on 1/2 bottle of Quikleen in a small day tank full of fresh 91 octane.
Run it, let it sit, then run out the rest of the gas the next day.
If that doesn't show marked improvement, try pulling the thermostat and running with the housing empty.
If that shows improvement, replace the thermostat with a new one.
Those two steps usually clean the idle right up, assuming the idle screw hasn't been messed with.

BTW, there's no clutching in a marine engine; the prop slip does that for you.
You are directly engaging forward and reverse gears and it is indeed hard on the gear train to shift above idle.

 

[DagsHuggy]

Thanks for the feedback.... sorry about the miss on terms, not a mechanic but learning I do like to try working on things myself.

 

[DagsHuggy]

so my next question would be where is the thermostat and is this a job that can be down while boat is in the water?

 

[Chigwalla]

The thermostat will be on the port side above the dipstick near the top of the crankcase and yes, it can be done with the boat in the water.

 

[DagsHuggy]

Again thanks.