Jump to content

Welcome to TheMalibuCrew!

As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account. It's free and it's easy, so don't hesitate to join the TheMalibuCrew Family today!

95 Sunsetter with 250 HP Mercruiser wont idle


Recommended Posts

I have a 95 Sunsetter with the 250 HP carbureted Mercruiser 350. It has been running and idling very well this year.(until now!) My son had it out today, and suddenly it stopped idling. I went out on a Waverunner

and was able to get it back to the house. It would keep running at 1200 or so RPM, but as soon as it idles down it kills. It will start right away by giving it throttle.

Boat has about 700 hours. I put in a fresh set of plugs and new Dist Cap and rotor on it about 10 hours ago.

Any thoughts on what might cause this?

Link to comment

Ethanol can damage your fuel system over time. You can double-check your plug wire installation. Do you use a torque wrench on your plugs? You can double-check the plugs too.

Link to comment

The not idling syndrome happened all at once, so I don't think it is ethanol deterioration over time (although that is something I will keep in mind.

I will check the plugs tomorrow (too hot right now). I did not use a torque wrench. In fact I was cussing whoever designed the exhaust manifold because I can't even get a regular plug wrench

to work. I have to use a very cheap plug socket likes comes with a motorcycle tool kit because it is the only thing thin enough to get to the plugs.

I'll let you know what I find.

Thanks!!

Link to comment

It's most likely a small piece of dirt in the idle circuit of the carb. The best way to clean it is to disassemble the carb, but you can try a quick fix by removing the air/fuel screws (if it's a holley carb they'll be on each side of the front metering block and if it's a carter type the 2 screws are right in front). First cover the top of the carb with an old towel to prevent gas from spraying all over, then use a rubber tipped air gun and give it a good blast of air. GENTLY screw the screws back in until the stop (DON'T force them past the stop) and then back them out 3 turns. This adjustment will be close enough to start it up and then do the final adjustment after it's running.

Link to comment

Sometimes you can just screw in the idle mixture screws to their seats, then back them back out, and it will clear the crap out... sometimes... but it is worth a try. Just remember to count the screw rotations to get it back close to where they need to be. And by all means change the fuel filter(s).

If neither of these work, and if you can keep it running at a higher idle, try either closing the choke butterfly some by hand. If the RPM pick up, you may have a vacuum leak somewhere. A hand over the open carb will work also... be careful.

If the air gun or closing of the mixture screws does work, I would get the carb rebuilt ASAP as well as change the filters and flush the line from the filter to the carb.

Link to comment

OK. I worked on the Sunsetter today and here is the scoop:

1.Plugs are OK.

2.Water separating fuel filter was changed this spring. Is there another one? If there is, it has never been changed.

3. I don't have air at my boat lift, but I pulled the idle screws out and squirted Carb cleaner in the holes.

4. I also dumped a can of SeaFoam in the gas tank.

Here is the current status:

1. Boat idles better but still not as good as it should. Above 1,000 RPMs it works fine. Same top end and plenty of power.

2. I pulled the flame arrestor and looked inside as the boat is running. When the boat idles down to about 700 RPM, there only appears to be

gas coming out of the right side venturi. When it idles up a little faster, then some gas also comes out of the left side, but not as much

as the right side. I was expecting to see a mist of gas, but the gas that comes out just seems to drip on the throttle blades.

3. When under way(above 1,000 RPM), gas seems to come out evenly on both sides.

4. I also tried adjusting the idle screws. Screwing them all the way in, and up to about 6 turns out does not seem to make any difference.

5. When the boat is pulled out of gear, it always dies. If it nurse it a little bit to keep it running, it will idle down but sputters and sometimes dies.

Any other thoughts are appreciated.

THANKS!!

Link to comment

If it's only feeding from one side of the carb venturis then it's running lean. When you close the choke plate it richens up the mixture and improves the idle quality. Obviously you have a piece of crap or varnish from evaporating fuel in one of the small passages. The best way is to disassemble the carb, rebuild, soak all the parts in carb cleaner (except plastic parts, use a compressor blow nozzle to blow out all holes and passages and reassemble it.

Link to comment

OK. I worked on the Sunsetter today and here is the scoop:

1.Plugs are OK.

2.Water separating fuel filter was changed this spring. Is there another one? If there is, it has never been changed.

3. I don't have air at my boat lift, but I pulled the idle screws out and squirted Carb cleaner in the holes.

4. I also dumped a can of SeaFoam in the gas tank.

Here is the current status:

1. Boat idles better but still not as good as it should. Above 1,000 RPMs it works fine. Same top end and plenty of power.

2. I pulled the flame arrestor and looked inside as the boat is running. When the boat idles down to about 700 RPM, there only appears to be

gas coming out of the right side venturi. When it idles up a little faster, then some gas also comes out of the left side, but not as much

as the right side. I was expecting to see a mist of gas, but the gas that comes out just seems to drip on the throttle blades.

3. When under way(above 1,000 RPM), gas seems to come out evenly on both sides.

4. I also tried adjusting the idle screws. Screwing them all the way in, and up to about 6 turns out does not seem to make any difference.

5. When the boat is pulled out of gear, it always dies. If it nurse it a little bit to keep it running, it will idle down but sputters and sometimes dies.

Any other thoughts are appreciated.

THANKS!!

The dripping seen is normal. The "misting" happens as the air flows more violently at high RPM's. The fireman is correct. It sounds like you have some crap stuck in there. If the RPM's only increased slightly when you closed the plate, I doubt there is a vacuum leak big enough to cause the stalling. If there was, the RPM's would have really picked up and it would have run allot better.

Back to the carb. When you took the screws out and sprayed cleaner in them, did you use the little tube and really spray in there good? If you remove the carb and turn it over, draining the gas out of it safely, you can spray up the idle mixture holes that are just below the plates. If you do this you want to back the screws out a couple of turns to open up the idle circuit a bit more. That is about all you can do unless you take the carb apart. But to do that, I would have a kit handy because the old gaskets will most likely tear.

Link to comment
martinarcher

These guys are right on. Time for a carb rebuild. Certainly some crap in the idle circuit. Levi will testify how important and big of a difference it makes. He can also testify how important it is to have all the gaskets you might need. Biggrin.gif

Link to comment

These guys are right on. Time for a carb rebuild. Certainly some crap in the idle circuit. Levi will testify how important and big of a difference it makes. He can also testify how important it is to have all the gaskets you might need. Biggrin.gif

Get a rebuild kit before you take it apart. I would also reccomend ordering new floats just in case. Its the best 12$ insurance policy you can get.

My boat ran like a Techumsa go cart with bad gas one day and like an F1 car the next. You will be happy!

Scope out this thread for more info, there is a SWEET pdf in there steping you through the re-build

Edited by Levi900RR
Link to comment

My boat ran like a Techumsa go cart with bad gas one day and like an F1 car the next. You will be happy!

That's a good oneROFL.gif

Link to comment

HEALED!!

I pulled the idle mixture screws out and gave it another shot of carb. cleaner. A friend of mine had just replaced the same carburetor on his Chapparal and

we looked at the bottom of it and found a piece of electrical wire the same size as the idle holes. I ran the wire through the holes and encountered a little resistance,

although there wasn't any gunk on them when I pulled it out. Started it up and it is now back to normal (actually probably better than it was before as I'm

sure some crud had built up.) It now also responds to adjusting the idle screws.

Thanks to everyone for all of the advice, counsel and suggestions!! You folks are AMAZING!!

Link to comment

HEALED!!

I pulled the idle mixture screws out and gave it another shot of carb. cleaner. A friend of mine had just replaced the same carburetor on his Chapparal and

we looked at the bottom of it and found a piece of electrical wire the same size as the idle holes. I ran the wire through the holes and encountered a little resistance,

although there wasn't any gunk on them when I pulled it out. Started it up and it is now back to normal (actually probably better than it was before as I'm

sure some crud had built up.) It now also responds to adjusting the idle screws.

Thanks to everyone for all of the advice, counsel and suggestions!! You folks are AMAZING!!

I would still suggest at a minimum taking the Airhorn (top of the Carb) off to make sure the bowls are not full of junk (I would check the screens on the float needles too). If it IS dirty you have only bought yourself some time until the next hunk of junk gets caught in there...

Good Luck!

Link to comment

Levi900RR,

Yes, I'm sure the whole carb needs to be cleaned/rebuilt, but hopefully this will get me through this season so I

can rebuild it without undue pressure. Its been roughly 40 years since I rebuilt a carburetor, so I

imagine I'll have a bit of a learning process to go through.

Link to comment

Glad to hear it's running again. Keep the fuel additive going in the tank when you fill it up and it may clean any remaining gunk out since it is flowing again. Have fun.

Link to comment
martinarcher

Glad to hear it's running again. Keep the fuel additive going in the tank when you fill it up and it may clean any remaining gunk out since it is flowing again. Have fun.

Good call. I bottle of Gumout carb cleaner in the tank will probably help get you through the rest of the season running well. It's always better to do overhaul work on the boat when the snow flies and the lake is frozen! Thumbup.gif

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...