3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

[kidafa]

Engine: 2005 Mercuiser Turn Key Start, Alpha One Gen 2 Drive Serial: 0W356097

After cruising for 10 minutes or so, when I come to a stop and turn the engine off it "Runs On" for a good 15seconds and I kill it by putting it back into gear when its off.

How can I fix this? Idle mixture screw turned CCW a bit maybe?

• Timing is checked and is fine
• Idle speed in Neutral is about 800RPM in Neutral and 710RPM in forward gear neutral

It doesn't run on anything like that when I turn it off on the muffs.

Also when I take off, If I try and ease it from idle all the way up to try and get it onto the plane, it hits a rough spot just above idle until 1,500RPM sometimes it stalls/almost stalls. If I dont try and ease it and just really gun it its fine....

Here is a video of my idle settings tied up to a dock:

Cheers in advance,

Chris

 

[bgc]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

A carbon build up causes this issue. There are several issues that can cause this the most common is a dirty carburetor. I would recommend a rebuild, and adjust. Seafoam is a shot term solution to remove the build up.

Do you spend much time idling/trolling?

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Well today was only the second time I've had the boat out I purchased it a few weeks ago...

Some of the fuel is old I've probably ran only 20L or so of fuel through it and the fuel that was in it when I purchased it was 4 months old but was hi-octane. Could this play a part?

Funny you ask today I did do some trolling and it didn't run on at all first time I took it out.

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

After doing some reading I'm thinking my slightly high idle may have something to do with it as I just Remembered I turned my idle up a tiny bit at the start off the day and the visor
Posted was from the first trip out....

Thinking I'll Try a tiny turn on the carb mixture Ccw and lower the idle a tiny bit

 

[Simoniz]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

My boat (similar engine) used to do this (running on) and Ive read loads of similar stories.

Changing the water pump impellor cured mine - if the impellor is weak then the cylinder head will run hotter than ideal and encourage running on.

Pinch the fat water hose between the water pump and thermostat when the enging is just idling, is it pressurised? Is the water feed hose along the top of the engine pressurised?

As for the hesitation, mine (with Mercarb) does it as well, but the boat otherwise runs well and I can live with it. I reckon its a design fault and the accellerator pump does not quite deliver enough extra fuel.

 

[Don S]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Idle speed in Neutral is about 800RPM

Right there is why it diesels so much. You have to get the neutral idle down to 700 or below and adjust the idle mixture like I said in your other post. Until you do that, you are going to have dieseling problems.

Forget carbon build up, that is not your problem.

 

[RogersJetboat454]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Like Don said lower the idle, and while your at it, make sure some one didn't do a tune-up with the wrong plugs.

 

[mpdive]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Idle is too high. I have the same engine and it calls for 600-650. The hesitation is probably your accelerator pump or a dirty or malfunctioning power valve power valve. Make sure to idle a 3.0 for a couple minutes before shutdown too.

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Thanks to all for the responses

I swear I remember reading in the service manual that you want it to idle around 700rpm in forward gear which made mine about 800 out of gear....

Anyway

Ill lower the idle and turn the idle mixture strew CCW as per don s's recommendations 1/8 to a 1/4 of a turn and see how I go.

Can someone give the low down on how to set both as best as possible on muffs?

Cheers,

Chris

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

UPDATE:

Lowered the idle today and played with the idle speed mixture screw.

Idles out of gear between 680 and 720rpm. Richened up (CCW) the idle mixture screw about 1/2 a turn. Doesnt run on at all on the hose, starts nice and easy and goes into gear so much nicer no clunking or anything

Question: How come If I start it it will idle at said RPM then if I give it a little rev to say 1500RPM it after that it will idle at about 750 and sl

 

[mpdive]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Pre load the cable. Your idle speed screw is not fully seated on the idle cam.

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

How do I do this? Remove the throttle cable from where it attached to the carb and loosen it a few turns?

 

[mpdive]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Yes. You are extending the lenght of the cable. When you put it back on it should have some tension on it keeping the throttle plates closed. To bad its not practical to have return springs on boats. How would you hold your beer then?

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Thanks mate.

"it should have some tension on it keeping the throttle plates closed" meaning the cable should have some tension on it or the throttle lever?

Just went to undo the nylock nut that holds the cable end onto the throttle lever and with not much force at all to try and undo the nut it just snapped the threads off :-( so theirs about 1 thread left before the shank.... Ill get some jbweld like stuff onto the end once ive got the cable back on.

View attachment 115063

 

[mpdive]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Well that just sucks. Another option that works is, take a dremel and cut a kerf around the shaft. Install a hairpin clip or circlip. I have had to do this before. Look at the accelerator pump shaft where it attaches to the linkage and you'll get the idea. It's safer then JB
Attachment wont open

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Yeah I was also thinking cut a small slot and install a circlip Ill yank on the stuff I've put on there tomorrow and see how it holds up....

As for the adjustment of the throttle cable:

remove then end that I've now puttied on (lol)
spin the black part/end of the cable so that its looser a little bit and there is less tension on the throttle cable so the idle screw touches the cam when its shut?

 

[mpdive]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

You will turn the brass barrel to lengthen the cable.If you can slide the cable on now without any effort, it's out of adjustment. you should have to push the cable slightly towards the barrel to get it to slide on. Easy way to explain it....Lay the eye opening of the cable right where it slides on the shaft. The holes should be slightly offset when adjusted properly.

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Ahhhh I see

Yeah thats how it is at the moment I have to push the cable towards the starter motor side of the engine to get it on.... So in hindsight if I have to push the cable towards the barrel slightly to slide it on when it is on and in place it in theory is forcing the throttle arm closed and right up on the idle cam, correct?

Was I meant to set the idle speed with the cable disconnected?

 

[mpdive]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Yes on setting idle speed disconnected and again after it is installed, work the throttle from the remote and make sure you are returning to the base idle you set previously. Good job mate!!!

 

[kidafa]

Re: 3L Runs On/Dieseling and Hesitates between 1,100-1,500RPM

Thanks for the help mate...

Seeing as we have the same donk in our boats. Take a small tool kit or anything out with you when you head out? If so whats in it?

Also 1 in 15 times I put the key in turn it to start and get nothing, turn it to off then over to start and it works then every time, is this something to be worried about/any idea what it could be or should I start a new thread?

Just trying to get this thing as mint as I can before our season starts here in Australia