# Sluggish I/O, sputtering questions?



## chuckinduck (May 28, 2003)

Was fishing out the port of manistee saturday night, and noticed my Starcraft islander began to sputter and stall out while trolling. We then figured we better run back to port, at which we pulled lines and started to head in. The boat was a dog out of the hole, and would sputter, and pop (almost like a backfire), and just generally be unresponsive. Every once in a while it'd get some legs under her and take off as if nothing was wrong, but eventually it would always bog back down under high speed. Idling, or starting up the boat, it would behave as normal, but under high speeds I'm having issues. When I rev the boat in neutral, the engine sounds fine. I pulled the spark plugs, and they're all fine, but I replaced them anyways. My engine is 1997 4.3L v-6 Mercruiser I/O engine. Anyone have any idea's of things I could trouble shoot. My initial thought was the engine has a gas issue, either its getting to much gas and flooding out, or something to that effect. Thanks in advance. 

Ryan


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## SalmonBum (Feb 28, 2001)

Change your cap/rotor. You can have a bad set and rev up and sound good in Neutral because no load. Put it in gear and it will run like heck.....


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## chuckinduck (May 28, 2003)

SalmonBum said:


> Change your cap/rotor. You can have a bad set and rev up and sound good in Neutral because no load. Put it in gear and it will run like heck.....


Thanks SB, I'll take a look at that.


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## mike the pike (Mar 11, 2008)

Check your water fuel seperator. When is the last time you replaced that???


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## tdejong302 (Nov 28, 2004)

I would suggest carb. cleaning


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## chuckinduck (May 28, 2003)

I replaced the fuel filter 2 years ago, which I believe is also the fuel/water seperator correct? It was changed when I put in a new fuel pump. Is there a particular way to clean out the carb?


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## Girtski (Apr 29, 2009)

Most units have a spin on water/fuel seperator filter and another smaller one inline near the carb. At least both of the Mercruisers I had did. One was a 4cyl 140 and ther other was a V8 Chevy 260. They should be changed every year. Cheap insurance. Depending when the last time was you did cap and rotor (if at all) I would go ahead and replace them too. There are other things that can cause your symptoms, but those are the most likely.


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## SalmonBum (Feb 28, 2001)

If I remember correctly, most Merc V6 motors do not have a fuel water separator. Only a Ceramic Fuel filter.


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## wally-eye (Oct 27, 2004)

Sea Foam is your best friend.........every fill up........just like an apple a day...:coolgleam


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## SalmonBum (Feb 28, 2001)

If you haven't changed your rotor at least once in the last 3 yrs, thats your problem. I just had a dockmate that had the same issue, Port motor would ilde and rev up in N, but sputter and stall in gear. He went thru fuel filters, carbs, etc.... THEN he asks me. $25 later for a rotot and shes running again. 


If you USE your boat and are running thru fuel and not letting it sit then fuel/carb is not the problem. People awlays assume that but in my experince is more the rotor. The rotors' connetions corrode very easy since they are in the marine enviroment. oNce that happens, then you have weak spark.It cannot ignite the fuel, acting as if its not getting fuel, but worse. Since its getting fuel but not burning your flooding the motor and don't even know it.

Oh yeah, check your dipstick. See if the oil level has raised or if it smells liek fuel. If so, you may have a bad fuel pump, if still mechanical on that motor (can't remember).


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## mike the pike (Mar 11, 2008)

wally-eye said:


> Sea Foam is your best friend.........every fill up........just like an apple a day...:coolgleam


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## FERG 06 (Oct 6, 2006)

chuckinduck said:


> I replaced the fuel filter 2 years ago, which I believe is also the fuel/water seperator correct? It was changed when I put in a new fuel pump. Is there a particular way to clean out the carb?


When you changed the pump did you change out the fuel line?
Depending how old it is it might not be alcohol rated. The ethanol will break down the rubber and it might be clogging up things. Happened to me. Just saying, might not be your fix but basically you need to go through everything like others have mentioned.


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## chuckinduck (May 28, 2003)

SalmonBum said:


> If you haven't changed your rotor at least once in the last 3 yrs, thats your problem. I just had a dockmate that had the same issue, Port motor would ilde and rev up in N, but sputter and stall in gear. He went thru fuel filters, carbs, etc.... THEN he asks me. $25 later for a rotot and shes running again.
> 
> 
> If you USE your boat and are running thru fuel and not letting it sit then fuel/carb is not the problem. People awlays assume that but in my experince is more the rotor. The rotors' connetions corrode very easy since they are in the marine enviroment. oNce that happens, then you have weak spark.It cannot ignite the fuel, acting as if its not getting fuel, but worse. Since its getting fuel but not burning your flooding the motor and don't even know it.
> ...


Yah, I pulled the dipstick saturday night when we got ready to run in. It looked fine, but the engine was warm. didn't smell any oil. I've ran 3 or 4 tanks of gas through it this summer, which is way down from years past, but you're right in thinking if it were bad gas, seems like it wouldn't be with brand new gas. I'll pull the filter since its been two years, along with the rotor and cap since its never been changed and try that first before I send it into a mechanic to let them nickle and dime me. I'll try that seafoam, I have a friend who swears by that stuff too. Thanks for everyones troubleshooting advice.


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## chuckinduck (May 28, 2003)

FERG 06 said:


> When you changed the pump did you change out the fuel line?
> Depending how old it is it might not be alcohol rated. The ethanol will break down the rubber and it might be clogging up things. Happened to me. Just saying, might not be your fix but basically you need to go through everything like others have mentioned.


Ferg, no I only changed the fuel pump, but I'll take a look at that as well. thanks


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## Steelmon (Mar 30, 2009)

I agree with the cap and rotor.

No offense but Sea Foam won't help eletrical problems.

Everyone should set up a Preventative Maintenance Program for their rig. Make a check list of all items down to the wheel bearings and run through it every spring:

Plugs & wires
Rotor & cap
Fuel filters
Trim pump level
Water pump
Outdrive
Bilge pump
Steering system
Shifters and cables
Prop & shaft [they can get line wrapped on them that chews up the seal]
Tires/bearings/brakes 
Wench and strap 
Lights
Etc. There's more I'm sure

An ounce of prevention-------


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## Quack Wacker (Dec 20, 2006)

I had a friend that had similar issues and it turned out to be the timing.


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## Steelmon (Mar 30, 2009)

Timing or points and/or condensor can cause firing problems. Add those to your check list. Check the points for pitting, while checking the cap and rotor.


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## chuckinduck (May 28, 2003)

Just an update. I replaced the distributor cap and rotor, and found quite a bit of corrosion on all six points of the cap. I also replaced the fuel filter and threw in some dry gas in the tank, just for good measure. Dropped it in a local lake lastnight (got quite a few odd looks as I launched a salmon boat on a smallish lake), and ran her up and down the lake for about 10 minutes, and it responded good. Thanks for everyones insight and help. I'll be able to salvage Labor day afterall.


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