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3.0LX Rough Idle, Stalls Out

T

Takedown

New member
Hi, new to the forum. I have a 1995 Starcraft 1710 I/O with the 3.0lx mercruiser in it. Got the boat basically for free and have been fighting an idle issue for a couple weeks now. I've replaced the fuel filter, water separator screen on the carb, cap, rotor, wires, spark plugs, did a carb rebuild and set the ign timing. Still having the same problem as I did in the beginning. Boat will start just fine and run great at any rpm over 1200 but anything below that benchmark the engine runs but shakes like mad. Doesn't appear to be misfiring or have a dead cyl either. It appears as if the electric choke is working as it should and I did put new gas in it recently to dilute the 1/8th tank of old gas. Still didn't seem to help the problem. I have messed with the idle screw and the idle mixture and it still doesn't seem to want to idle properly at around 750-800. I haven't done a compression test but I plan on it tonight but I just wanted some input from you guys.

Could this be a sign of a weak coil or cracked distributor? Ideas????

Here is a video of it idling below a thousand rpms. Its one of the very few times that Ive been able to get it to atleast.
https://www.youtube.com/watch?v=z1YVb4ucY7A
 
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On a boat that old, the hoses from the tank to the engine are suspect. Unless they were replaced with ethanol resistant hose, its likely that the lining of the hose has dissolved in the ethanol and likely deposited as a thin film inside your carb where it will cause all kinds of havoc. Had my engine suddenly refuse to run below 1300 RPM and it turned out to be a hard sand colored deposit partially blocking one of the jets of the carb. Commercial solvents would not touch it, had to be mechanically chipped out. Chris @ Dockside says that the he cleans the carbs with an ultrasonic cleaning machine.
 
I was looking at how to describe my problem in a new post but maybe we have the same problem? I have a Merc 25 HP 2 stroke on a 14' Starcraft. Boat shop said the compression was good, when i finally got it into the water, it would run pretty good then bog down and barely go at full throttle. When i hooked the Earmuffs after I got it home I saw a small water leak coming from the head. Took the boat back, they found the head was warped from corrosion after a new gasket install. The head had to be sent out, welded and leveled, They also rebuilt the Carb. After I got it back the boat still bogged down, looked again and water is coming out of the water ejection cover. I took it off, added gasket seal. Water Coming out of behind one of the bolt holes.
I recently replaced Both Coils, got 30$ Spark Plugs and new wires, New Gas Tank, Fuel Lines, added a Water Filter Seperator, REC 90 + Sea Foam Treatment. Took it out to the Intercoastal and wouldnt start after it was Hot. Water was coming out of the ejection port the whole time. Almost got stranded and needed a tow.
Took a while to figure it out but I put it into the warm up position in throttle and it finally started with more fuel.
Got it home again, water leaking again through the water ejection cover.
So, maybe water getting into the Cylinder? The boat used to start right up at the least even though it didnt run good untill i did the tune up.
Long winded but, check your Head Gasket, etc? Maybe the timing is off not with the tune up? Maybe a fuel pump going bad. Im not sure being this is my first boat.
Hope this helps you and maybe someone can help me? Of course the Serial Number is worn off my motor.
 
sandkicker said:
On a boat that old, the hoses from the tank to the engine are suspect. Unless they were replaced with ethanol resistant hose, its likely that the lining of the hose has dissolved in the ethanol and likely deposited as a thin film inside your carb where it will cause all kinds of havoc. Had my engine suddenly refuse to run below 1300 RPM and it turned out to be a hard sand colored deposit partially blocking one of the jets of the carb. Commercial solvents would not touch it, had to be mechanically chipped out. Chris @ Dockside says that the he cleans the carbs with an ultrasonic cleaning machine.
Click to expand...

I did infact have this exact issue. I had a ton of sand like material in my water separator filter on the carb I had to clean out before the rebuild and was wondering how it had gotten past the fuel filter. The carb is clean as a whistle now though. The bowl and jets are spotless and flow like they should.
 
I will add to that once I'm able to get it to idle somewhat ok once I give it throttle then return it to the idle position it will stall out.
 
Takedown said:
I did infact have this exact issue. I had a ton of sand like material in my water separator filter on the carb I had to clean out before the rebuild and was wondering how it had gotten past the fuel filter. The carb is clean as a whistle now though. The bowl and jets are spotless and flow like they should.
Click to expand...

That "sand like" material did not get thru your filter/seperator. It is formed by a chemical reaction of the water in your gas with the ethanol and possibly any anti ethanol chemicals you used. I've seen that in my carb bowl ( after a 10 micron filter) and as I've stated that is the same stuff that was firmly stuck in one of the carb jets.
 
Hi,

not to open a new thread - will co tinue here ss I have the same problem...

No ethanol in petrol here.
Also all the petrol is fresh, 2 weeks max.

I bought the boat last year, was running almost fine. Idle was sketchy as it was cutting out often, despite being set to 1.000rpm later. Especially when put in gear.

Becauae state of manifold and raiser was unknown and I use the boat in salt water, I had the MF and raiser replaced. Plys a complete service.

This year - it runs even worse.
Idle goes up an down out of gear 700-1.100rpm, I smell petrol, cuts out often when put in gear. If survives put in gear, needs a bit of throttlecto run. 1.000rpm minimum.

It also shakes a lot when at arround 1.800rpm.

Above that it runs fine, tops 28knots as i run this 18' boat on very conservative prop.

Any idea about this messy idle?
 
I'm having a similar problem this year, it didn't happen last year. I started using ethanol-free fuel last year and it was running fine. However, at the start of this year the engine was shaking like crazy at an idle, not it won't even low idle properly. I have a Starcraft Mercruiser 120, with a Rochester 2Jet carb. At the controls, next to the forward/reverse I have a second handle which seems to boost the RPMs, maybe puts more air in? Not sure what to call it or what exactly it controls. Usually I use it to start and then can shut it off. But it's the only way to keep it running at an idle, I have to boost the rpms up until I'm ready to shift & drive. Once I get a little throttle speed it's OK. But return to idle and it goes all rough and stalls out. So I'm thinking it's idle air screws, or passageways plugged, or maybe its vacuum leaks that's I've been learning could also do it.
 
Hi,

I was just called by a mechanic that went to check the situation.

Somehow ignition timing was 25deg off.

Need to do the test run for myself to check the current situation and report it.
 
Hi,
a litle update...
Idle after setting the ignition right - totally better.
Never had a stall during shifting since.
I did notice a slight "floating" of idle speed between 750 to 900rpm when hot.
Before - I cold see anything between stall and 1.100rpm.
So much much beter - but i guess not perfect still.

Engine runs smooth in most cases, but still has one glitch.
Runs ok up to 2.000rpm.
When i go over 2.000 and up to 2.500rpm - engine chockes and shakes while running.
Over 3.000rpm - smooth again.
And this is absolutley repeatable. When I start from marina all OK.
I increase rpm slowley up to 2.000rpm - all smooth.
When I touch the throttle just a tad - first goes to 2.100 and immediately chokes and stumbles down to 1.200 - 1.500rpm and shakes, coughs.
I just need to ad a bit of throttle to pick up and when exceeds 2.500rpm it smoothes out to completley smooth at 3.000rpm.

Any ideas?
 
I suspect your accelerator pump in the carb is a bit weak.

See if there's a carb linkage setting where you can increase the squirt of the accelerator pump and set it at maximum squirt.

Jeff
 
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