'87 merc 3.0 stalls when warm & bringing back to idle

[Jns1981]

'87 merc 3.0 - starts and runs great. After an hour or two of pleasure boating the engine stalls when brought back to idle-cant start for a few minutes. Seems to need a cool down period but then starts up and runs just fine. Idle is fine before I run it for a while.

There is a slight lag/hesitation on throttle up depending on how fast it accelerates.

History:

Had new cables, & alternator installed last year (just bought it this year) brand new battery 3 weeks ago.

Plans:

-Check idle at carb

-check spark

-Replace fuel filter

-Check cables-could they be messing up idle if not properly set?

-Possibly timing?

Any other ideas to add to the list?

The engine stalls hot when shifted back to neutral. Right now it just means I dock a bit fast and throw in reverse.

 

[merc120_81]

I chased a similar issue for a while, it seemed heat realated. Everyone always says, its not the ignition coil, but mine actually turned out to indeed be the ignition coil.

 

[Jns1981]

yep, that's why I want to check spark-but I'd have to check under similar conditions, right?
Bah. Don't want to throw money at guesses. But then again, I don't have a timing light-have to throw some money into the hole in the water...

 

[harleyman1975]

You can buy a timing light for $20.00

 

[Jns1981]

realize that- poor wording- have to spend a little for a light, why not spend a little more for a light and coil.. small thing gets the ball rolling, it rolls fast!

any other ideas regarding stall causes when hot?

 

[Jns1981]

Ok. Throttle cable was preventing idle adjustment. Tweaked that, replaced fuel filter and ran out our light (late start). When I went back to the mooring, it stalled around 2800rpm. Did I mess with idle too much? It's around 700 in neutral. Checking coil tomorrow.... What does a weak spark look like? I've read "check for weak spark." A spark is a spark, right?

 

[salty3rd]

I chased a similar issue for a while, it seemed heat realated. Everyone always says, its not the ignition coil, but mine actually turned out to indeed be the ignition coil.

Yep I've seen/ heard the same thing, but once I hear it gets warm and starts acting up it tells me their is an electrical issue; resistance= heat; I would change the coil. Even if it isn't,having a spare on board is not a bad thing.

 

[merc120_81]

if I where you, I would do the coil. I chased mine for some time.. Spark should be crisp and blue, but its kinda hard to look at that out on the lake, when the engine is warm enough to have the problem. I think the coil was around $30 it wasn't expensive.

 

[kenny nunez]

Get a new rotor and have it ready when the engine stops. Replace it and do not be surprised if it re starts. They get so hot that they will go to ground . Give it a try.

 

[Jns1981]

Ok! I think I know what I did. Adjusted the idle mix & flooded. Tweaked that & replaced what looked like a 30 year old original coil & it ran and idled well- No Stall!!!

Family had a blast on The Hudson!

Thanks for all the suggestions.

 

[merc120_81]

congrats. Good work.

 

[merc120_81]

Congrats, it always feels good when it gets running! Glad you had some fun with the boat, thats what they are for isn't it???