Mercruiser 3.0ltr will not stop

[donie]

Hi all<br /><br />My Merc 3.0 (2000 model) will continue to run (roughly) when I switch off the key. How is this possible? It sometimes continues for about 10 seeconds and it's like as if it's firing on one cylinder? <br /><br />If I let it idel before stoppping it sometimes stops normally.<br /><br />I'm a bit worried that it'll damage itself doing this as it sounds awfuly rough and lumpy.<br /><br />Thanks for any help.<br />Donie

 

[andy h]

Re: Mercruiser 3.0ltr will not stop

I just bought a boat yesterday and took it out for the first time, it has the same motor as yours and ran perfect until i shut it off it did the same thing but only for 3 or 4 seconds so i am very interested in the answer also.

 

[a.d.mobile]

Re: Mercruiser 3.0ltr will not stop

how high is the idle? could this be run on after shut off? this is a bad thing with a boat idle should be 650 to 700 in gear while in lake no more! try that the bad effect of this is hydro locking when a motor run backwards and draws water in the cyls.....

 

[donie]

Re: Mercruiser 3.0ltr will not stop

I'm not sure what you are asking me to do here?<br /><br />Donie

 

[andy h]

Re: Mercruiser 3.0ltr will not stop

mine is set at around 800 I will try to lower it a little tonight.<br /><br />Donie- there is a idle adjustment screw you will need to back out if your ideling too high.

 

[donie]

Re: Mercruiser 3.0ltr will not stop

OK, I will try that too. SOmebody also mentioned here (off list) that the mix was too rich. The transom at the back was very dirty last week from exaust fumes but I cleaned it up. <br /><br />Would this be an issue and if so, how does one go about make the mex a bit leaner without doing damage.<br /><br />Thanks<br />Donie

 

[DJ]

Re: Mercruiser 3.0ltr will not stop

Donie,<br /><br />Yes, a rich mixture can be a contributing factor to your problem. The rich mixture causes deposits to form in the combustion chambers. Those deposits "glow" and act like spark plugs.<br /><br />First, you may have to rebuild your carb.<br /><br />Second, get an internal engine cleaner. The best I used is GM Top Engine Cleaner. There are equivelants-I'm sure.<br /><br />Third, make sure the idle is set to spec-in gear-in water.

 

[chris in va]

Re: Mercruiser 3.0ltr will not stop

The 2002 Sea Ray I rented today with the 3.0 did the same exact thing. I shut off the motor, and it hiccupped a couple times before stopping. Weird.

 

[akriverrat]

Re: Mercruiser 3.0ltr will not stop

people will compensate for poor idle by treating the symptom. they just increase the idle speed. this keeps the throttle butterfly from closing enough and you get run on. at best you need a tuneup and mixture adjusted and idle speed screw backed off to let butterfly close to where it should be at idle. at worst start with the carb rebuild and spend from there.

 

[akriverrat]

Re: Mercruiser 3.0ltr will not stop

oh yeah... just as you should avoid full throttle untill the engine warms up you should allways try to let engine cool down at idle befor shutting it down. working a cold engine hard and shutting down a hot engine without a short cooldown period will shorten the life of the motor.

 

[donie]

Re: Mercruiser 3.0ltr will not stop

Hi again all,<br /><br />Sorry for the delay in getting back about this. I followed the procedure in the manual and brough the idel revs back from 1200 !!! to 750. Made a huge difference, fixing both this problem and making it quiter to put in gear.<br /><br />I also adjusted the mixture using the procedure from the manual and this has made the engine run a lot sweeter.<br /><br />I was wary of messing with this stuff as I'm not a mechanic by any means but I can do some stuff. The boat is only a 2000 model with very low hours so I assumed it wasn't in need of tuning.<br /><br />How wrong I was. Thanks for all the help in getting this sorted.<br /><br />Donie

 

[donie]

Re: Mercruiser 3.0ltr will not stop

On a related issue, if the engine was become clogged up with carbon or whatever from an over-rich mixture, do I need to clean it or with the leaner mix burn off the deposits no that the mixture is correct?<br /><br />Thanks<br />Donie

 

[donie]

Re: Mercruiser 3.0ltr will not stop

Sorry I was in too much of a hurry and that last bit makes no sense. Here it is again....<br /><br />On a related issue, if the engine has become clogged up with carbon or whatever, from an over-rich mixture, do I need to clean it with an engine cleaner or will the leaner mix burn off any deposits now that the mixture is correct?<br /><br />Thanks<br />Donie