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Outboard Maintenance Question

3,690 Views | 38 Replies | Last: 7 yr ago by sunchaser
Pescado Borracho
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Motor is a 2001 Mercury 2 stroke 40 hp. Engine will start easily, but idles roughly and dies on it's own. I can press the primer bulb as it's starting to die and it will idle back to normal, then start to die again. Or, I can slightly throttle up, just barely engaging the throttle, and it idles smoothly. Without any throttle or primer bulb, then engine dies. Fuel in the tank is fine, and I drained and flushed the carbs as well and it hasn't helped. Any ideas what to try next? The boat doesn't get enough use, maybe it just needs the piss run out of it? I do not use ethanol-free fuel, but treat it with sta-bil 360. Thanks for any help.
A.G.S.
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AG
What's the longest you've had it running? Using the choke?

It could just need to be run a bit, at least let it warm up all the way.

Not as familiar with newer motors, but there may be an idle set screw you could adjust.
Finn Maccumhail
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AG
Have you gotten the compression checked? Sounds like you're not getting enough fuel into the cylinders at the low idle to keep it running.
Potcake
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AG
Maybe a bad fuel line connection or bad bulb not keeping a prime?

Regarding the fuel and stabilizer, our mechanic said we shouldn't be using Sta-bil in gas containing ethanol because it will clog up lines and carb. Happened to some of our boats and TWDB boats. There is a stabilizer made for ethanol fuels. We use one made by Lucas Oil.
Pescado Borracho
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A.G.S. said:

What's the longest you've had it running? Using the choke?

It could just need to be run a bit, at least let it warm up all the way.

Not as familiar with newer motors, but there may be an idle set screw you could adjust.
I ran it off muffs in the driveway on Sunday for probably 10-15 minutes just barely engaging the throttle to keep it alive. I kept thinking it would get better but it never did.

I replaced the spark plugs and primer bulb, and dumped the fuel water separator mid January and it purred like a kitten. Unfortunately it hasn't been run since then, and now it's doing this.

I had thought about messing with the idle set screw, but I keep thinking this is the wrong thing to do since I have been happy with it's current setting for the two years I've owned the boat.
magnumtmp
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AG
It's either fuel pump or an air leak on the suction side of the pump (keeping it from pumping). That's where I would start anyway.

Take the fuel pump apart and check for holes in the rubber diaphragm. Could be trash in there too.

Next thing after that is to take the carb off and clean it....sounds like the idle jet is fine, but the high speed jet could be plugged/dirty.
Pescado Borracho
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Finn Maccumhail said:

Have you gotten the compression checked? Sounds like you're not getting enough fuel into the cylinders at the low idle to keep it running.
No I have not. What is the root cause for not enough fuel to the cylinders? I have experienced the current symptoms in the past, and it was usually due to water in the fuel after sitting for too long. I would dump the fuel water separator, drain and flush carbs, drain fuel tank, run the bad gas out and then it would run like a top as long as I used it.
Furlock Bones
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AG
I would replace the fuel lines and your filters again. Ethanol has a bad habit of corroding lines and sending chunks into filter clogging it.. Anything built before 2009ish, time frame would benefit from this realtively cheap insurance.

I will find some photos later when I'm back in my office of what can happen.
adefect
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magnumtmp said:

It's either fuel pump or an air leak on the suction side of the pump (keeping it from pumping). That's where I would start anyway.

Take the fuel pump apart and check for holes in the rubber diaphragm. Could be trash in there too.

Next thing after that is to take the carb off and clean it....sounds like the idle jet is fine, but the high speed jet could be plugged/dirty.


Where I would start as well
magnumtmp
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AG
To add to my post above, the only other thing that comes to mind is carbon build up in the exhaust, choking the flow. I doubt it's that, this would slowly chew into performance, not a sudden change. You can check for dirt dobber nests. Your exhaust probably comes through the prop, not sure. Some older OMC units had two holes near the top of the lower unit....perfect entrance for dirt dobbers.
magnumtmp
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AG
Ok, one more tip....I keep thinking of stuff....

That's either a 2 or 3 cylinder, right? If the hoses and pump checks out, use an IR gun to check the head temps as it idles. If you have a cold cylinder, you can narrow it down.....i.e., clean that carb first.
SanAntoneAg
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AG
Didya replace the fuel filter?
Pescado Borracho
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magnumtmp said:

Ok, one more tip....I keep thinking of stuff....

That's either a 2 or 3 cylinder, right? If the hoses and pump checks out, use an IR gun to check the head temps as it idles. If you have a cold cylinder, you can narrow it down.....i.e., clean that carb first.
3 cylinder
Pescado Borracho
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SanAntoneAg said:

Didya replace the fuel filter?
The in-line filter? No I have not yet.
IslandAg76
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do you have the vent screw on the fuel tank filler cap open?
SaltwaterAg17
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+1 in regards to the fuel pump
Furlock Bones
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here's what could potentially be happening to your engine. highly suggest changing out your fuel lines regardless.

http://www.bbcboards.net/showthread.php?t=21733





Pescado Borracho
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Thanks for the info. If this is the problem, how would the engine run fine with throttle but not at idle?
Pescado Borracho
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Anyone?
Potcake
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AG
Maybe there is some small space between the inside of hose and blockage. At idle, maybe not enough pressure to "squeeze" through it but with more fuel pushing past it with throttle it is enough? Pulling ish out of my butt at this point.
Comeby!
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I think this is what's happening to my mercruiser. Still runs for a few seconds after the power is cut.
Salt of the water
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Cheap compression check. Take off the cowling and fire it up at a fast idle so it doesn't die. Pull the spark plug boot on one cylinder and listen. Then put that boot back on. Repeat until you've done all three cylinders. Was there a major sound difference with any single cylinder not running? If so that cylinder may be your problem.

Are you self mixing your oil? What ratio are you running at? If the motor calls for a 100:1 and you eyeballed a 50:1 and got it too rich that could cause some idle issues. You'd be seeing smoke though.
Pescado Borracho
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I'll try the compression check, thanks. So I should expect a difference once I pull a boot off, and I am looking for a different difference between one of the boots vs the other two? Sorry just trying to make sure I know what I am listening for.

I am self mixing oil at 50:1 using one of those oil mixing bottles. Not really seeing a bunch of smoke in the exhaust.

Motor is actually a 2002, looked at the title at lunch. Not sure if that matters or not.
Salt of the water
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The motor will run "rough" once you pull a boot and that cylinder stops firing, but it shouldn't die. It should spool back up to "normal" once you reinstall the boot. You want to look/listen for a noticeable difference in performance after dropping any of the cylinders. If it's idling poorly because of one of your cylinders, it may not run any different once you pull the boot for that cylinder. Then you have a dead giveaway which one is the issue, but I doubt you'll get that lucky with diagnosis.

My little 2 cylinder outboard had a rough idle when I got it. I could tell that one cylinder was the issue because it idled worse without that plug on than the other. Pulled out the spark plugs and the "bad" one was noticeably dirtier than the other. I got lucky and new plugs solved my problem.

Most of the last of the 2 strokes called for 100:1 but running 50:1 shouldn't hurt anything.

When you cleaned the carb are you sure you got it all back together? Sometimes there's a small pin or spring that you may not notice is missing that can cause issues if missing.
IslandAg76
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AG
Careful--there's a reasonable amount of electricity running thru those spark plug wires.
reddog90
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Salt of the water
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Good disclaimer. There's a few different types of insulated tools made specifically for pulling spark plug wires. I've always just been cautious but I bet vatozone has some cheap puller tools that would increase safety.
Pescado Borracho
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Thanks for the clarification.

I didn't actually break the carbs down and clean them. I just unscrewed the drain plug on each one and flushed them with fresh fuel via the primer bulb.

I will check the fuel lines and make sure they aren't breaking down. Do you guys think I should also order rebuild kits? I feel like I should probably take the carbs apart the clean them real well and replace all the gaskets.
SanAntoneAg
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AG
And replace the fuel filter.
Pescado Borracho
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Yeah will do.

Should I get a full repair kit or just a gasket kit?
txags92
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AG
+1 on changing the filter and consider replacing the prime bulb. You are either starving the carb for gas before you throttle up because the fuel filter is gummed up and the engine isn't pulling enough vacuum, or you are getting an air leak into the line before you throttle up and start pulling enough vacuum. The most likely place to get that air leak and the cheapest to fix in my experience is in the primer bulb. Those things wear out and lose their flex over time.
wamvoss
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If you didn't completely clean the carb, it's a high probability that your low speed jets are clogged up. You might get lucky and just back out the idle jet screws and clean the out with carb cleaner and air pressure. Be sure and count the turns when you back them out. If your motor runs with partial choke you have a restriction.
If that doesn't work, get a manual, carb kits and completely clean them.
SanAntoneAg
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There you go Borracho, the solution is as clear as mud.

Start simple, then dive in deeper if needed.
akag77
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I would sell it and get a Yamaha
Pescado Borracho
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Alright thanks. I'll start with gasket kits, carb cleaner, and fuel filter and see where I get. Hopefully I don't need any repair kits, they are pretty expensive.
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