# spark plugs .how often do you change them



## freyedknot (Apr 10, 2004)

how often do you change your plugs,especially on the big hp motors. i do mine twice a year and maybe 3 if i troll with the 40 hp. i always change them for the start of duck season cold weather.


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## Iowa Dave (Sep 27, 2009)

Depends. My Mercury manual says to change/inspect every 300 hours on my Verado and I'm sure that applies to all 4 strokes. 2 Strokes would be more often I would think a lot would depend on how much you troll or run wide open to clean them off and if you use any additives to clean the carbon out of the system as well.


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## johnrude (Mar 29, 2009)

every spring on a 2 stroke that is used quite often. and always carry an extra pair.


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## UFM82 (Apr 6, 2004)

Why? 

UFM82


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## peple of the perch (Sep 13, 2004)

I agree with UFM82. If they look fine and work great than why bother. However plugs are inexpensive and by replacing them it gives you a semi-visual on how well your motor is running. My opinion is just give them a little cleaning and they'll be fine. Unless the electrodes are pitted or melted. But if that is occurring there is something wrong with the motor.


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## Workdog (Jan 10, 2007)

peple of the perch said:


> I agree with UFM82. If they look fine and work great than why bother. However plugs are inexpensive and by replacing them it gives you a semi-visual on how well your motor is running. My opinion is just give them a little cleaning and they'll be fine. Unless the electrodes are pitted or melted. But if that is occurring there is something wrong with the motor.


Agreed (except that plugs, at least mine, are not inexpensive--$5-6+ a plug and I need 12 for twin motors, and I shop for price). I do a compression check several times during the fishing season, and check my plugs at that time. I usually go 250-300 hrs on my plugs, whether straight running or trolling. I seafoam the cylinders when needed.


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## freyedknot (Apr 10, 2004)

cuz , someone said they have been runnin on the same plugs for the last 3 years?


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## LEfriend (Jun 14, 2009)

....... I seafoam the cylinders when needed.....[/QUOTE said:


> How do you determine "when needed" From the compression check? When you say seafoam the cylinders, how much do you use. That is how much gas and what seafoam strength do you mix it? Do you just add seafoam to your normal boat tank and run during normal operation. What is your process and how frequently do you find you need to do that?


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## BigDaddy300 (Nov 1, 2004)

freyedknot said:


> cuz , someone said they have been runnin on the same plugs for the last 3 years?


Thats the kind of someone that blocks the ramp or needs help back in when the motor won't start!


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## Workdog (Jan 10, 2007)

LEfriend said:


> How do you determine "when needed" From the compression check? When you say seafoam the cylinders, how much do you use. That is how much gas and what seafoam strength do you mix it? Do you just add seafoam to your normal boat tank and run during normal operation. What is your process and how frequently do you find you need to do that?


When I do a compression check, while the plugs are out, I look in the cylinders and see if there is a "chunky" look to the cylinder heads. However, I'll typically do a decarb with seafoam every 50-70 hours (depending on if I have the time to do it). There are several ways to do a decarb, and a lot depends on what type of motors you got. With carborated motors, while running at idle you would pull the cover off the carbs and spray the seafoam/Deep Creep directly into the carbs until there is a thick smoke pouring out of the motor. Then, spray all carbs hard to choke out the motor (or have someone shut the motor off. Put the motor back together, wait 15 minutes, and take it out on the lake to run the motor under load (2,000-2,500 rpm or so). The carbon in the cylinders should have melted and burn off as you're running the motor. For EFIs like my Merc 150s (and DFIs/4 strokes), You could run the motor on a hose at the house to heat up the pistons, shut it off, pull the plugs and spray seafoam into the cylinders (half a can per motor or so), wait 15-20 minutes then turn the motor over to blow out excess fluid, then take the boat to the lake and run the motor(s) under load. Under load does not mean full throttle, just 2,000-2,500 rpm or so. I've put the seafoam in like this in an evening, then taken the boat to the lake the next morning. Another method is to pull your fuel water separators and pour seafoam in them before reinstalling (not my preferred method). The last, and probably best way to decarb is described below by Dunk from thehulltruth.com and other sites:

"_dunk decarbon

This works for Carbed, EFI, Ficht, HPDI, Optimax and even 4 strokes... 
First you need a separate small fuel tank. One of those 3 gal red Tempos works great or an empty gal milk jug will also work, but might be a bit messier.. 

I use Seafoam over the OEM stuff like OMC Engine Tuner or Merc Power Tune because in the last few years they changed the formula and you have to let them sit up 12 hours. Who's got time for that?? Seafoam you can buy from NAPA, CarQuest or other auto stores. Seafoam works in 15 mins. 

You'll need 3/4 gal of gasoline and one 16oz can of seafoam for each engine. Don't forget to add 3oz of oil if you are premixing in a carbed engine. Use about 3 ft piece of fuel hose off the little tank. You connect this tank to your engine by pulling off the main tank fuel hose off the intake side of your water separating fuel filter and plug the hose off the small tank on to that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If you have an engine that has fuel plug then you need a fuel plug on the little tanks hose. 

Start the engine, let it warm up and start pulling the mix into the engine. You may have to increase the idle to keep it running once she get loaded with the Seafoam. Run the engine 15 mins in the dock or just cruising around under 2500. Then shut it down and let it sit for 15 mins. Restart the engine, the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 mins. If she smokes after the second time do it again, but I've never seen one still smoke after three doses. The gallon mix should be enough to do this 3 times. You don't need any wide open throttle, you don't need to change the plugs. If it's cleaning the combustion chambers it's also cleaning the plugs, but every 50-60hrs is good time to change plugs in most engines. 

I cleaned a antique evinrude one time that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the mix through it. Seafoam has been around since the 30's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards. 

You guys with the 4 strokes think you are immune from this? Those engines work 10 times as hard as any auto engine ever will and they will carbon up. I bought a Bronco two years ago that had 95,000 miles on it. When I used seafoam on it I had the neighbors hanging out of their front doors looking for where the fire was after I started it the first time there so much smoke. 

Too many are under the assumption that it's totally the 2 stroke oil that causes the carbon, Wrong... it's also the additives they put in the fuels today. The carbon inhibitors in 2 stroke oil are there for this reason also. Remember when gasoline used to smell like gasoline, today it smells more like bad cologne. 

For those guys that like to do the carbon treatment by spraying it down the carbs Seafoam also comes in spray can called Deep Creep. It's the same stuff under pressure. Says right on the can Oxygen Sensor Safe, for you Yam guys. 

After that if your engine maunf recommends a daily additive treatment then do that in the mean time, but all 2 stroke outboard need decarboned every 50-60hrs. If I owned a 4 stroke I would do it the same. Once you are set up with the tank and hose the Seafoam is only 5-6 bucks can. It to easy not to do it_"

Hope this helps.


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## LEfriend (Jun 14, 2009)

THANKS! ..... good info, will save this one.

Steve


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## Lewzer (Apr 5, 2004)

Once a year after I run it once to get the winterizing stuff out of the cylinders. Also pull them periodically and clean them on the wire wheel that on my grinder. Makes them good as new.
25 hp 2 stroke Mercury.


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## UFM82 (Apr 6, 2004)

1) Fact- I have the same plugs in my outboard that were in there when I bought the boat. That was 2007. My boat starts and runs fine. 
2) My plugs cost about $4- NGK's. They might do better than others because they are "gapless" or or whatever they are called. I have a center electrode but no "arm" for the gap. It simply jumps to the body of the plug. theoretically I should never have to change plugs unless the center is damaged. 6 plugs is $24. Not gonna bust the bank but why spend it when it isn't needed?
3) Do you replace plugs in your car/truck several times a year or once a year? Why in your boat engine then?
4) A fouled plug IS NOT ruined. It's wet. Or it has deposits on it. Wipe it off, dry it off or clean it off and it's just fine. Would you throw away a fishing reel because it got wet?
5) If the engine runs fine, why mess with it? I've found that many times people trying to do "maintenance" screw the engine up worse by ruining plug wires, damaging wiring harnesses or other stuff just trying to change a plug. if it ain't broke, don't fix it. 

UFM82


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## K gonefishin (May 4, 2004)

My Optimax manual says every 100 hours but when my dealer pulled them at 136 they were fine. I started to get a small hesitation when coming out of the hole around 150 so I replaced them at 161 hours when my boat was at the dealer getting a coil replaced. My dealer told me replace them when you think they need to be replaced based on performance of which I did. My motor does run better since replacing. At 10-12 bucks a crack I wasn't in a hurry to replace them so I took my dealers advise and not Mercury's. I don't use my motor to troll if I did with the amount of trolling I do I would probably change them twice a year and use additives MUCH more than I do. Since my big motor is only used to get me to and from spots.


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