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Bad performance top end


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I have a 2003 Malibu Sportster. At about 2.5 rpms or so @ 25-30 mph the engine starts to sound like it is bogging down a bit and its not crisp. Something is certainly wrong. At first, I thought it was water in my fuel as I left my gas tank cap off for a bit one afternoon while running the boat. However, I changed the water/fuel filter separator and there was no water in it, which lead me to think that wasn't the issue.

Then I realized all summer I had been putting in 87 Octane when 89 Octane is recommended. So I'm now thinking its bad gas and has gummed up the carb somehow. I changed the sparkplugs and 4 of the 8 plugs were an absolute mess. I put in some 91 Octane in the engine and ran that for about 15 minutes or so out on the lake to see if the plugs were the sole culprit and while it did run a tad better the top end is still not right and the engine is still sounding funny.

I checked the flame arrester and the line into it and it was clear. My exhaust/intake is clear as well. I have not changed the fuel filter as of yet.

When the boat is in neutral and I rev up the engine it sounds glorious and crusing around at low speeds it does fine as well. It's just when I get it about 25 mph and 2.5 rpms or so that it starts happening. The boat starts like a champ and idles fine when it warms up for a few. I've only got about 85 hours on it as I bought it when I started to have babies and that didn't leave a lot of time for the last 4 summers.

Does anyone have any suggestions on next steps? I'm wondering if I should run it longer high end with the better gas to see if that does anything, but I'm kind of concerned that will make it worse, especially since I'm not 100% sure what the problem is.

Thanks for your time,

POW

Edited by pow
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It never hurts to run better fuel but i dont believe that is your issue. Change the fuel filter for sure if it has been a while, and take a look at your cap and rotor. Check your plug wires for cracks, this is something you would not notice till you get a load on the engine. Use a spray bottle in the dark and spray a mist of water over the plugwires and look for some sparks.

If all of the above are good then maybe your carb does need a bath.

good luck

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when you say "the plugs were an absolute mess"... what exactly does that mean? Black and wet? white and chalky? running 87 octane fuel will not cause your plugs to foul, or your carb to gum up. the only thing it would cause is pre-ignition, or knock, which can certainly destroy your engine, but that doesn't seem to be the problem.

Of course, the carb may indeed be in need of a bath, and the ignition system in line for some freshening, but none of these problems would be caused solely by running 87 octane fuel.

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Am having the same trouble with mine, 89 Skier!

Check presssure on fuel pump. On a newer boat yours prob isn't mechanical though.

I'm going to change cap, plug wires, and points and condensor this weekend. I'm sure you have electronic ignition though.

1 bottle of dry gas and/or carb cleaner would clear up yours.

Fouled plugs would be noticed at idle or accelerating too.

Will let you know what works.

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MAKE SURE YOUR OIL LEVEL IS NOT TO FULL . MY 97 CARB RESPONSE WAS DOING THE SAME THING AND IT WAS OVER FULL , PROBABLY FROM CARB LEAKING DOWN WHEN SITTING

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Being that you had a water seperator you might want to get a bottle or two or fuel dryer. if there was enough water in the fuel to make it past the seperator and effect running of the engin, you may have some water in the carb. bowl as well. Good luck in gettting this resolved.

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Isn't that motor in your Sportster Fuel Injected? or am I wrong?

Another thing you might check is Cylinder Compression.

Standard motor for that boat was the 310 carb until 2005.

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Isn't that motor in your Sportster Fuel Injected? or am I wrong?

Another thing you might check is Cylinder Compression.

Standard motor for that boat was the 310 carb until 2005.

Gotcha, I wasn't sure...Is there a reason it would "require" 89 octane as the topic starter said?

Could be time for a Carb Job.

Edited by areamike
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I believe all indmar motors "require" 89....probably driven by compression ratio.

Thanks for the replies.

The bad plugs where basically black and grimmy. Several of them had a a couple of oil rings on them which is curious. The boat doesn't seem to burn oil, however, when I do start it up and rev it up I sometimes get blue smoke for several seconds.

Also, any chance I'll harm the engine if I run it when it starts to get rough for an hour or so to get rid of the remaining fuel?

Edited by pow
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I believe all indmar motors "require" 89....probably driven by compression ratio.

Thanks for the replies.

The bad plugs where basically black and grimmy. Several of them had a a couple of oil rings on them which is curious. The boat doesn't seem to burn oil, however, when I do start it up and rev it up I sometimes get blue smoke for several seconds.

Also, any chance I'll harm the engine if I run it when it starts to get rough for an hour or so to get rid of the remaining fuel?

Is there something wrong with the gas? why would you run it all out? If there is something wrong with it then pump most of it out with a hose down the fill hose and a pump. It really sounds like you are in need to a tune up and not much more. The smoke could be valve seals or something that would dry up and leak with the boat being 5 years old and only having 80ish hours on it. I would do the cap, rotor, plug wires and use some lucas oil treatment. Then if still needed give that carb a once over.

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I believe all indmar motors "require" 89....probably driven by compression ratio.

Thanks for the replies.

The bad plugs where basically black and grimmy. Several of them had a a couple of oil rings on them which is curious. The boat doesn't seem to burn oil, however, when I do start it up and rev it up I sometimes get blue smoke for several seconds.

Also, any chance I'll harm the engine if I run it when it starts to get rough for an hour or so to get rid of the remaining fuel?

Is there something wrong with the gas? why would you run it all out? If there is something wrong with it then pump most of it out with a hose down the fill hose and a pump. It really sounds like you are in need to a tune up and not much more. The smoke could be valve seals or something that would dry up and leak with the boat being 5 years old and only having 80ish hours on it. I would do the cap, rotor, plug wires and use some lucas oil treatment. Then if still needed give that carb a once over.

I apoligize for being a new noob, but what is the "rotor"?

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I believe all indmar motors "require" 89....probably driven by compression ratio.

Thanks for the replies.

The bad plugs where basically black and grimmy. Several of them had a a couple of oil rings on them which is curious. The boat doesn't seem to burn oil, however, when I do start it up and rev it up I sometimes get blue smoke for several seconds.

Also, any chance I'll harm the engine if I run it when it starts to get rough for an hour or so to get rid of the remaining fuel?

Is there something wrong with the gas? why would you run it all out? If there is something wrong with it then pump most of it out with a hose down the fill hose and a pump. It really sounds like you are in need to a tune up and not much more. The smoke could be valve seals or something that would dry up and leak with the boat being 5 years old and only having 80ish hours on it. I would do the cap, rotor, plug wires and use some lucas oil treatment. Then if still needed give that carb a once over.

I apoligize for being a new noob, but what is the "rotor"?

What a cap and rotor is

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