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amarfanhar

Engine running rough even after tune and carb rebuild

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amarfanhar

I just got home from a great week long trip to Lake Powell and my boat gave me some serious greif. It was the first time out after my winterization performed by my local malibu dealer.

I have a 93 echelon with 500 hours with a 350 merc, carborated.

After putting the boat on the water I noticed a strange engine vibration but thought it would go away after the engine warmed up and thought nothing of it. After a continuing rough enginge ride of 45 minutes to meet everyone at the houseboat, I put the boat into idle and it would not run on idle. After being stranded in the bay, I was able to get it started but only at 2000 rpms or higher.

On the water I checked the spark plugs and they were black with charcoal like soot on them and rusty so I tried to take a wire brush to them all. After I cleaned the spark plugs I was able to run it a little bit better at 1500rpms but still no idle.

I took it into Page, AZ to Larrys Marine and he replaced the spark plugs, distributor cap and the engine still would not idle. Then we found out the engine was dumping gas and diagnosed a dirty carborator. When he took it apart it had all bunch of sand and gunk in it. After he rebuilt the carb, we fired it up again and it idled great but was running really rough almost like the timing was off. So he checked the timing and everhthing looked good with the timing. He then said go run the motor as much as you can over the next couple of days and it should run smoother with more use.

I put in 91 octane gas. I ran it for 5 days hard and it still is running rough. :cry: It stutters when you try to give it full throtle to pull a waterskier out of the water. It sound rough and is still giving me vibrations that I wasn't getting last year. Any thoughts?

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boatswaiyn

Have you replaced the fuel filter lately? I have been down 4 weeks in lake powell over the last 2 years with my boat and have yet to make it a week without boat problems. Last year we replaced our fuel pump twice. We had it replaced the first time and then ruled it out when it still was running bad. Turned out that the new pump they put in was failing to begin with. I would get a hold of a fuel pressure gage and see if you are holding around 40 psi.

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Michigan boarder

Sorry to hear about a lousy trip.

Could the coil be going out, providing a spark but not a strong one? Or just bad coil connections? Plug wires maybe? If the fuel pump is bad won't it under-fuel?

So the symptoms are still similar, just lesser in magnitude? My far-from-unprofessional guess is that there is an ignition problem. I think you had an ignition issue to begin with, then coincidentally had a fuel issue arise with the carb, but still have an ignition problem. Maybe put another set of plugs in, as the first were replaced before fouling by a rich mixture from a dirty carb?

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JasonK

Sounds like the start of my problems long ago. Took an early trip to the Masters (Georgia) in April, and took my boat to ski the local lakes. Before we went, I summerized the baot and ran it for one day at home(Michigan) It was pretty cold out, but it ran fine. Once we got down there, I put the boat in a Georgia lake and it runs rough. Tried to ski, but just wasn't happening. End of the day, I removed the water-seperating fuel filter, and it was full of water. After putting a new filter on, we were able to ski the rest of the trip, but it still ran rough sometimes. That summer I had my carb rebuilt. The guy said it looked to be in good shape.

Did you clean or adjust the points in your distributor? or replace them? They can be tricky to install just right.

Another problem I've had was a bad water-seperating fuel filter that wouldn't seal and let air into the system. That was a tough one to find. I replaced hoses, added a filter with sight tube, bypassed the w-s filter housing. And now a days It seems my choke isn't opening when cold. Twice this year I had to open the butterfly by hand to get it to start.

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Michigan boarder

Sounds like the start of my problems long ago. Took an early trip to the Masters (Georgia) in April, and took my boat to ski the local lakes. Before we went, I summerized the baot and ran it for one day at home(Michigan) It was pretty cold out, but it ran fine. Once we got down there, I put the boat in a Georgia lake and it runs rough. Tried to ski, but just wasn't happening. End of the day, I removed the water-seperating fuel filter, and it was full of water. After putting a new filter on, we were able to ski the rest of the trip, but it still ran rough sometimes. That summer I had my carb rebuilt. The guy said it looked to be in good shape.

Did you clean or adjust the points in your distributor? or replace them? They can be tricky to install just right.

Another problem I've had was a bad water-seperating fuel filter that wouldn't seal and let air into the system. That was a tough one to find. I replaced hoses, added a filter with sight tube, bypassed the w-s filter housing. And now a days It seems my choke isn't opening when cold. Twice this year I had to open the butterfly by hand to get it to start.

You mean close the butterfly, right?

Forgot about the points, good idea, my 94 is electronic ignition. A bad gap would definitely cause those symptoms.

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skyskier

My first thought is the carb float is not adjusted properly, a saturated float, or the needle and seat valve is not sealing. I know the carb was just rebuilt, but any of those three could still be the problem.

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amarfanhar

Sorry to hear about a lousy trip.

Could the coil be going out, providing a spark but not a strong one? Or just bad coil connections? Plug wires maybe? If the fuel pump is bad won't it under-fuel?

So the symptoms are still similar, just lesser in magnitude? My far-from-unprofessional guess is that there is an ignition problem. I think you had an ignition issue to begin with, then coincidentally had a fuel issue arise with the carb, but still have an ignition problem. Maybe put another set of plugs in, as the first were replaced before fouling by a rich mixture from a dirty carb?

I think you are right. Something is not fireing properly. Figureing out where that problem is...is not my expertise. I had the fuel filter replaced when I winterized the boat. I don't think the fuel system is the problem it is the ignition.

I would think the irregular vibration means one of the cylendars isn't firing like it should. But I just put new plugs in, distributor cap, checked the timing, and made sure all the plug wires were going to the right plugs from the distributor. I think this problem needs a professional not me guessing around.

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Woodski

I am going to make am assumption here based on the fact you have a '93 Echelon. If a Mercruiser, it should have the Weber carb with an electric choke on it. Those do need to be adjusted as the bimetal spring that controls the choke is not quite calibrated to a wide temperature range. What might have happened is the choke remains closed for too long and too tight, thus causing a very rich mixture resulting in a fouled spark plug(s)(black and sooty as you noted). When warming up, is there a lot of black smoke out the pipes, if yes this is at least a problem. To adjust you loosen the three phillips screws on the side of the carb that attach the chok mechanism (right or starboard side/black circular device) and twist in the edirection you need, don't quote me but I think ccw, but if you look down the carb you can watch the choke move as you do it so you go a couple of notches looser or less choke). The plugs can foul quickly so the problem will repeat very quick. Weak spark or too big a plug gap will augment that particular problem as the soot becomes a spark barrier. You might have to get another set of plugs or clean the existing set again.

Float level can also lead to a rich mixture.

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Michigan boarder

I am going to make am assumption here based on the fact you have a '93 Echelon. If a Mercruiser, it should have the Weber carb with an electric choke on it. Those do need to be adjusted as the bimetal spring that controls the choke is not quite calibrated to a wide temperature range. What might have happened is the choke remains closed for too long and too tight, thus causing a very rich mixture resulting in a fouled spark plug(s)(black and sooty as you noted). When warming up, is there a lot of black smoke out the pipes, if yes this is at least a problem. To adjust you loosen the three phillips screws on the side of the carb that attach the chok mechanism (right or starboard side/black circular device) and twist in the edirection you need, don't quote me but I think ccw, but if you look down the carb you can watch the choke move as you do it so you go a couple of notches looser or less choke). The plugs can foul quickly so the problem will repeat very quick. Weak spark or too big a plug gap will augment that particular problem as the soot becomes a spark barrier. You might have to get another set of plugs or clean the existing set again.

Float level can also lead to a rich mixture.

Those are great suggestions that (if cleaning & not replacing plugs) don't cost anything, can't hurt to try it. Reminds me of a choke issue I had years ago with a 2.3L Ford, same symptoms as described by Woodski.

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Surfin247

Same symptoms I had on the 95 Echelon Merc Carb. even after a new carb. Found the wire that runs from the electric choke to the altenator was corroded. Cleaned and tightened it pushed it back on the altenator post. I was good to go. To tell if your choke is working properly start engine run RPM's above 800 and after a min or so feel one of the three brass scews if its hot your choke is at least getting power. Setting it to the right level depends on your boat and local conditions.

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JasonK

I've got a coiled choke on mine, and a "pull-off"? .

Michigan Boarder: I had to open the small forward butterfly. I need a choke education, meaning... someone needs to look at with me. But, when the boat wouldn't start, both butterflies were all the way closed. Once I open the small one just a bit, it would start.

Normally, it looks like as soon as I turn the key, the butterfly opens a little, and it starts. Twice, I've turned the key and it didn't open and didn't start. I have no experience working on carbs. Is the "pull-off" the problem?

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amarfanhar

I checked the choke with the flame arestor off and it looked like it was working fine when running. It still running really rough. I can get the rpms up to 4-5000 and it is running in idle it's just not sounding right and has more vibration than normal.

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Woodski

Amarfanhar, I assume you mean the choke plate is open or not restricting any air getting to the carb? I would pull the plugs and take a look, if they are sooty and black again, then the mixture is most likely your problem. If they look tan or brown then there is someting else amiss. If sooty and you clean or change them, start the engine with no choke, manually hold it open or disconect it and see if the problem persists. One other thing I would check, you have removed the plugs a few times, check to make sure you have the right plug wires on the right plugs, the firing order is on the intake manifold and probably the distributor cap also or you can look it up online (small block chevy). Crossed wires will make it run rough. Is that 4-5000 rpm under load or with the boat out of grear?

Jason, that makes sense, you have too much choke, loosen the three phillips screws and move your choke line a couple of notches (per description earlier).

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Michigan boarder

And remember, check those points (if you have them). It seems stupid and simple, but we've all done stupid things before with plug wires and basic components, so I'd say go thru your checklist one more time:

-make sure the plugs are clean

-plug wires on the right plugs. Might even be a good time to change those too.

-points? If so, change and gap them

-make sure the cap & rotor are on properly and are clean

Lastly, if you get it running well, I'd change out that oil. You don't want carbon fouled oil in that engine all summer.

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amarfanhar

Thanks for all the insight. I will double check all of the above and let you know what I find.

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JDubya

Fire it up and inspect the wires in the dark to look for arching. If the wires are old you could have a wire with a pinhole and it would run like its missing.

Sounds like a bad gap, bad wires, or f/a mixture issue (carb adjustment).

BTW, firing order is 1-8-4-3-6-5-7-2.

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amarfanhar

Head gasket. I'm getting her fixed with a little extra juice.

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