Dirty Fuel?

[Luke V.]

Hey Folks!

Wondering if you might be able to shed some light on my issue.

My outboard is a 2009 Mercury Sea Pro. 20HP. 2-Stroke

The last few times I have had it out it likes to hesitate/mis-fire when I am running it wide open. Then it began happening from idle all the way to WOT. The odd thing is, is that it does not do this every time. Some days it will happen once, others it will happen the entire time.

 

At first I thought it was a bad plug, so i looked at them they seemed good, but replaced anyway. Problem continued, so I turned to fuel aditives. Thinking that the fuel may be dirty, moisture etc. I started with using just the Marine Stay-Bil(blue Kind) mixed it with a few tanks and it never really improved my problem. So I picked up some sea foam, Have ran this the last two times I have used the boat and still does not seem to do anything about the problem. Today I used Sea Foam, Stay-Bil, Brand New Gas, and Brand New Oil and it still has the same problem.

 

The only thing left that I can think of is a dirty/plugged fuel filter. Can these be cleaned manually? Or should I look at replacing them? It looks like there are two different ones on the motor.

 

For gas mixture i am mixing 14oz of oil to 22 litres of gas. I use Quicksilver Outboard Oil(not cheap but it is recommended). I use regular pump gas and always have with this motor.

 

Thanks for your time and help in advanced.

Luke

[Dutch]

Time for a tune up.

 

Probably a combination of gummed up carbs and the fuel delivery system.

 

I don't subscribe to the bad gas theory, ever.

[Sour_Squirrel]

x2 on carbs gummed up.

 

Did you run a batch of gas that had been sitting in the fuel tank for a while?

 

The best thing you can do with gas in your tank is to always treat it with fuel stabilizer. I always use the Marine fuel stabilizer by Stabil.

 

 

[Luke V.]

The gas never sits more than a week. The motor was run/used 2-3 times a week since the end of April.

[John Bacon]

 

Hey Folks!

The odd thing is, is that it does not do this every time. Some days it will happen once, others it will happen the entire time.

 

 

 

Is there any coorelation between rain and humidity and the severity of the problem.

 

It happens, or gets worse when it has been raining then I would suspect am issue in the ignition system.

[davey buoy]

The gas never sits more than a week. The motor was run/used 2-3 times a week since the end of April.

 

I'm leaning towards a bad coil. Your symptoms are exactly how a coil can act up.

This may or may not include a bad wire or cap.

If you can start it up at dark and see if you can see any sparks jumping around.

Edited October 8, 2012 by davey buoy

[Luke V.]

Rain/humidity has no increasing effect on it. I don't think it's a wire, they look brand new, not cracked.

I just took apart/cleaned both fuel filters found some sand in the primary filter. Didn't find any in the secondary filter. Also on the secondary filter the bolts were loose. I believe that air could have been gettin into the fuel and changing the mixture.

[Sour_Squirrel]

Remove the filter(s) and clean them with gasoline.

Try some carb cleaning spray.

 

If the problem is still there you could have a sticky reed valve(?)

[Luke V.]

I used carb cleaner when I cleaned them

[bigbuck]

What about air getting into the fuel line?? Does the ball stay hard after you've run for a bit? What condition is the fuel pickup like in the fuel tank?? Work back from the tank to the motor ruling out potential suspects.

[Luke V.]

Tank is the same age as the motor. Line is new last year. Ball stays hard all the time. I have never notice it going soft. I'll have a look at the pick up in the tank

[ecmilley]

sounds like you have eliminated the most common fuel issues, one of the things on the mercs is there known for coil and ignitor problems can you determine which cylinder it is? have you done a spark plug change? i change plugs in carbed two strokes every year.

if you can determine the mis-firing cylinder i would suggest you move the coil and wire assemblys around if the misfire follows the coil change the coil

[davey buoy]

sounds like you have eliminated the most common fuel issues, one of the things on the mercs is there known for coil and ignitor problems can you determine which cylinder it is? have you done a spark plug change? i change plugs in carbed two strokes every year.

if you can determine the mis-firing cylinder i would suggest you move the coil and wire assemblys around if the misfire follows the coil change the coil

 

Exactly Luke V,as again mentioned. That is your problem. Easy to change.Been there,done that more than a couple of times.

.Air leak will cause the motor to bog down. Will not be intermittent.Remember air is a lot easier to suck than liquid. Good luck sir!!.

[Luke V.]

Thanks for the replys guys. After cleaning the filters last night I put it in the water and gave her a run. Ran just as good as new.

Got dark brought it home.

To look into the coil. I switched the coil pack from one to the other.

Put it in the water again today and it ran just as good as yesterday.

I will continue to watch this and keep a spare coil with me just on case

[davey buoy]

Thanks for the replys guys. After cleaning the filters last night I put it in the water and gave her a run. Ran just as good as new.

Got dark brought it home.

To look into the coil. I switched the coil pack from one to the other.

Put it in the water again today and it ran just as good as yesterday.

I will continue to watch this and keep a spare coil with me just on case

 

Let's hope that was your problem,it's the intermittent backfire which tells me it's not fuel related. Usually when a filter gets blocked it doesn't run good one day and not the next. Stranger things have happened.:thumbsup_anim:So you did change a new coil and tested with each cyl?.No change? I guess your on to it.!!