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rkloeppel

Top End Sputtering

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rkloeppel

Need some help!

My 2007 boat with a 383 Hammerhead motor has been experiencing top end sputtering. It started this spring at lower speeds but after 15 minutes of running, it only occurred when running at higher speeds especially when the 4 barrel kicks in. Problem....when I get on the throttle and pushing speeds of excess of 45 mph the motor starts to sputter. Sometimes it will run really strong and then slows down sputtering......very inconsistent.

I have added a ton of additives to the gas tank to clean the fuel lines and carburetor but still experiencing issues. I also replaced the fuel filter thinking maybe there was water in the line...no change.

Someone thought it might be an electrical problem...spark plugs, distributor cap, wires.

Motor has 76 hours on it.

Any ideas!!!

Thanks for your help!

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85 Barefoot

Need some help!

My 2007 boat with a 383 Hammerhead motor has been experiencing top end sputtering. It started this spring at lower speeds but after 15 minutes of running, it only occurred when running at higher speeds especially when the 4 barrel kicks in. Problem....when I get on the throttle and pushing speeds of excess of 45 mph the motor starts to sputter. Sometimes it will run really strong and then slows down sputtering......very inconsistent.

I have added a ton of additives to the gas tank to clean the fuel lines and carburetor but still experiencing issues. I also replaced the fuel filter thinking maybe there was water in the line...no change.

Someone thought it might be an electrical problem...spark plugs, distributor cap, wires.

Motor has 76 hours on it.

Any ideas!!!

Thanks for your help!

You don't have a carburetor first of all.

Secondly, have you changed the fuel filter? I'd start there. You getting any water in your oil or is it rising? Was the boat winterized properly? What prop? What are rpms? Any chance you're hitting rev limiter?

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Ndawg12

You don't have a carburetor first of all.

Secondly, have you changed the fuel filter? I'd start there. You getting any water in your oil or is it rising? Was the boat winterized properly? What prop? What are rpms? Any chance you're hitting rev limiter?

He said he changed it. But what about a screen, isn't there a screen in a hose on the inlet side of the fuel pump somewhere?

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Jimmypooh

You don't have a carburetor first of all.

Secondly, have you changed the fuel filter? I'd start there. You getting any water in your oil or is it rising? Was the boat winterized properly? What prop? What are rpms? Any chance you're hitting rev limiter?

Plus1.gif That's my thought too. Are the RPMs dropping for a long period of time or does it sound like it's pulsing? 45MPH is about where you should max out so it sounds to me that the engine is doing what it's suppose to. You can also raise the RPMs in neutral and see if it sounds the same. You will get to a point where the computer will not allow the RPMs to go any higher and it will sounds like the engine is pulsing. That's normal, protection from the engine blowing up.

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85 Barefoot

He said he changed it. But what about a screen, isn't there a screen in a hose on the inlet side of the fuel pump somewhere?

yep, sorry

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rkloeppel

Thanks for your help!

I should have given you some additional info on the boat and motor.

The boat is a jet boat with a carburated 383 Hammerhead motor. I added the post since most 383 motors are installed in Malibu boats.

The boat will generate speeds of 60-65 mph.

I pulled the fuel pump and found it clean. I then checked the bronze filters entering the Holley and found them clean. I believe the fuel is getting there.

I am starting to think it must be electical issue, maybe a sensor.

With the boat wide open it will start pulsing and then run strong, then start pulsing again. No pattern at all.

Edited by rkloeppel

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rkloeppel

Thanks for your help!

I should have given you some additional info on the boat and motor.

The boat is a jet boat with a carburated 383 Hammerhead motor. I added the post since most 383 motors are installed in Malibu boats.

The boat will generate speeds of 60-65 mph.

Oil level is fine since changing to a racing oil. Boat has been properly winterizied every year.

I pulled the fuel pump and found it clean. I then checked the bronze filters entering the Holley and found them clean. I believe the fuel is getting there.

I am starting to think it must be electical issue, maybe a sensor.

With the boat wide open it will start pulsing and then run strong, then start pulsing again. No pattern at all.

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stooy

When was the last time you changed the plugs? I have had quite a few problems caused by plugs over the years...

Cheers

Stewart

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rkloeppel

When was the last time you changed the plugs? I have had quite a few problems caused by plugs over the years...

Cheers

Stewart

I haven't with the boat having 76 hours. Think I should along with the wires and distributor cap?

Thanks for your post!

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Steve B.

Still sounds like it's hitting a rev limiter.

Steve B.

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85 Barefoot

Still sounds like it's hitting a rev limiter.

Steve B.

On a carbureted engine?

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rkloeppel

Still sounds like it's hitting a rev limiter.

Steve B.

I know that is not it. This is happening between 4000 and 5000 rpm. Without moving the throttle and running between that rpm range the motor will surge and then sputter, surge again then sputter.

I just can't get a grip on this issue.

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skiguy

I would plug in a fuel pressure gauge and monitor that when the problems start happening. If your fuel pump is going bad or there is some obstruction in the gas line this method should point you in the right direction.

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rkloeppel

I would plug in a fuel pressure gauge and monitor that when the problems start happening. If your fuel pump is going bad or there is some obstruction in the gas line this method should point you in the right direction.

Good point....I did think about that and priced them on Jegs website. Just need to figure out where to place it.

I'm also planning to do a tune up with cap, wires and plugs.

Thanks!

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rkloeppel

Well, replaced the fuel filter, fuel pump, cap, rotor and spark plugs.......still pulsing at higher end.

Took it in to the local dealer.....can't figure it out.

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rkloeppel

I thought the same thing but I replaced the fuel pump and filter then cleaned the in-line filters on the Holley.,,,,no change.

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ColinP

On a carbureted engine?

Yep, rev limiter can be ignition cut or fuel cut, or a combination of the two. On a carb'd engine the rev limit is controlled by the ignition system.

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rkloeppel

Thanks......I took it in to a Malibu dealer in St. Louis.

I did what I could......now for the professionals to figure it out.

Thanks for everyones help.

I will let you know the final verdict.

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JustinOSU

did you check the timing?

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rkloeppel

did you check the timing?

I did not......it doesn't sputter all of the time. I can have the throttle all out and it will run great and then drop 300-400 rpms and sputter. Then run great again.

There is no pattern to it at all....not even from one outing to another.

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Engine Nut

Thanks......I took it in to a Malibu dealer in St. Louis.

I did what I could......now for the professionals to figure it out.

Thanks for everyones help.

I will let you know the final verdict.

What RPM does your engine turn at wide open throttle? The wide open throttle operating range for that engine is 4800-5200. If you are turning much over 5200 that could be part of the problem.

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rkloeppel

What RPM does your engine turn at wide open throttle? The wide open throttle operating range for that engine is 4800-5200. If you are turning much over 5200 that could be part of the problem.

Top End on the boat is 5000. I can be running at 5000 and then the motor will drop to 4600 for 5-10 seconds and then return to 5000. Sometimes it won't do it at all, other weekends the motor will sputter.

You really notice it at a dead start....if you get on the throttle hard it will really sputter and then catch itself.

I know these are extremes but this all started at the beginning of the season and it is driving me nuts.

Edited by rkloeppel

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rkloeppel

What RPM does your engine turn at wide open throttle? The wide open throttle operating range for that engine is 4800-5200. If you are turning much over 5200 that could be part of the problem.

Larry.....I changed the spark plugs and installed MR43LTS based on your email. What gap should they be at? I put them in 0.060 based on the manual.

Trying to eliminate possible issues.

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Engine Nut

Larry.....I changed the spark plugs and installed MR43LTS based on your email. What gap should they be at? I put them in 0.060 based on the manual.

Trying to eliminate possible issues.

MR43LTS should be at .045 not .060.

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