Spare Spark Plugs

#1
Sea Doo went to the trouble of including holders for three spare spark plugs in the lid of the cargo compartment. Why did they do that? Who thinks it's necessary to carry spare plugs with them and why? Even the tool kit has a plug "wrench" (heaven forbid I should ever have to use it :)). This all implies that it's not uncommon for plugs to go bad while on the water. Should I stow spare plugs on my rigs?
 

racerxxx

Moderator
Moderator
#2
Probably a carry over idea from the 2 stroke days. But I will say I've seen many guys come here looking for help in running issues and plugs fixed them up. It's cheap insurance, would you rather limp home or cruise home?
 
#3
It is a misconception that the 4tecs do NOT foul plugs. Even though these are 4 strokes, they don't act like the plugs in your car that will last 100,000 miles. I've seen plugs foul just a few minutes after installed. Not a bad idea to use the holder and carry plugs with you.
 
#4
This extra set of plugs can get you going again if you happen to water foul your plugs. To avoid engine damage, stop running if the engine isn't making power like it should b/c damage can result.

Make sure to always run the factory recommended correct plug for your engine b/c the incorrect plug generally won't run correctly or cause damage (pre-ignition, for instance). Change them immediately if one does foul or avoid running the engine.
 
#7
My old 95 XP went through plugs, like Patton used to say, like CR@P through a goose. On my 4-tecs, I always change them at the end of the season, and I have never had to change them during the riding season.
 
#9
Considering the difference in how a car engine is operated vs a marine engine, I think that helps explain why any marine engine MIGHT need the plugs changed more often due to fouling.

Therefore "mileage may vary" is a reasonable conclusion, right? Gotta say based on the precision of fuel injection, I could easily imagine 4-tec plugs exceeding 200hrs by a wide margin, just as a modern outboard can clock over 8k hours.
 
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JTR

New Member
#10
I tend to disagree, I could maybe believe that because the Rotax RPM is run in the 7000 and it could wear the plugs quicker. But the 4 stroke fuel injected engine is the same whether car or marine. Imho it would be difficult under normal operation to foul the plugs, air/fuel is always adjusted by the cpu. If plugs are fouling it's another problem. I would check the gap and adjust.
 
#12
If plugs are fouling it's another problem.
And the operating conditions present challenges that add complexity. Lack of maintenance can be a biggie ("it's another problem").

Not just Rotax turning at 7,000 RPM, it's the marine environment. Lots of things can happen. For example, lets say you hit a wake and flipped upside down briefly and some crankcase oil vents through to the intake, enters the cylinder and glazes onto the hot plug insulator causing contamination? Or the ski sits around for a little too long and the fuel gets a little stale or water, and glazes the insulator during a hard run your average car is unlikely to experience. Who are that nobody that rides WOT across the lake like there's no tomorrow, does he drive his car that way too? I doubt it, thus the root cause might even be the nut behind the wheel.

Please don't claim it's a car, this is misleading b/c generally speaking, a marinized engine runs with a more conservative tune using a colder plug than automotive engines, less aggressive ignition timing and a richer air/fuel mixture because the marine environment is considerably (not slightly) harsher in comparison. Marine engines are burning a heck of a lot more fuel (measured in GPH as opposed to MPG) than an automobile engine loafing down the highway @ 1800 RPM. This translates to considerably more heat.

High duty cycle with no coasting up to stop lights or down hills, on and on.

The marine engine is a beefed up version in comparison and the 4-tec as far as I know doesn't benefit from an O2 sensor in the exhaust (it's a wet exhaust) as used by automotive computers to monitor air/fuel stoichiometry. For marine FI engines at least up until recently, there's just a simple lookup table used to produce a conservative air/fuel ratio approximation based on throttle angle, RPM and intake manifold vacuum + added safety of slightly richer mixture to compensate for (un?)anticipated harsh conditions.

So on top of high power requirements, burning one heck of a lot more fuel and as a result making a heck of a lot more heat, the air/fuel ratio is considerably richer for the purpose of maintaining a reasonable safety factor.

Add this all up, and 200 hours reasonably represents IMO, an accomplishment.
 
#13
Sea Doo went to the trouble of including holders for three spare spark plugs in the lid of the cargo compartment. Why did they do that? Who thinks it's necessary to carry spare plugs with them and why? Even the tool kit has a plug "wrench" (heaven forbid I should ever have to use it :)). This all implies that it's not uncommon for plugs to go bad while on the water. Should I stow spare plugs on my rigs?
Actually, it implies that people will do stupid shit and without further advice, try to start their machines after they've rolled them in surf. For crying out loud, the damned plugs are there for a reason as is the wrench. If you roll your shit, pull the damned plugs, turn it over and see if water shoots out. If not, resue your old plugs. If so, use the new ones. Ignorance IS NOT a reason to be a dick.
 

Sea Dood

Premium Member
Premium Member
#15
If you think spark plugs are not an issue with 4TECs, then you don't know much about them. If the ski is running fine on the water, however, it is rare they go bad. The usual time they fail is after dewinterizing or just after sitting for a long time.

My lake house is a quarter mile from the main ramp. Every summer I have guys stopping in front of my house because their ski is running like sh1t. One time I told a guy his plugs were bad. He said " I am a mechanic, plugs don't go bad like this" He was pissed and being a prick. I told him I bet him $100 it was the plugs. He said OK smart guy, you have a bet. I went to the garage, grabbed three new plugs and tools and returned to the dock. 5 minutes later, he started it up, took off, it ran perfect, and I was surprised he actually came back. He looked embarrassed, but took out his wallet. I told him to just pay me for the plugs. Gave me 50 bucks as he said I saved his day on the water
 

Sea Dood

Premium Member
Premium Member
#18
Sounds like the kind of mechanic who'd rebuild a motor twice, for the same seized cylinder.
No, he was an auto mechanic. Plugs on cars these days last 100K miles, they almost never go bad, so he was comparing a ski to a car. His ski was relatively new, so he thought there was no way the plugs could be bad.

It is common for 4TEC plugs to go bad every season, usually from fogging.
 

Sea Dood

Premium Member
Premium Member
#19
the spark plug change on a 1503 is 200 hours but on a 1630 it is 100 hours.
Those numbers don't mean a thing, those are just Sea Doo recommended numbers. Again, these numbers make people think the plugs are a rarely replaced item, when it is not true. They fail all the time.
 

JTR

New Member
#20
Sorry do not agree, they rarely fail. It is another problem that affects the plug, not the plug itself. Plugs can last forever, if the gap is increased by wear, just regap. So much $$ wasted on replacing good parts.
 

Chester

Premium Member
Premium Member
#21
I fix them for a living and I see them foul several times a year on different customers PWCs. It doesn't matter if it's a Jet-Ski, WaveRunner, or Sea-Doo, it happens on all brands.
I just tell them to replace them annually, they're cheap.

Chester
 
#22
I was showing what Sea Doo Recommended to clarify a earlier post showing 200 hours on a 4tec . I put 100 hrs a year on a ski as do most of my friends, so on my 300 thats new plugs at least once a year. Of course I am lucky enough to be able to ride most of the year and never winterize.
 
#23
No, he was an auto mechanic. Plugs on cars these days last 100K miles, they almost never go bad, so he was comparing a ski to a car. His ski was relatively new, so he thought there was no way the plugs could be bad.

It is common for 4TEC plugs to go bad every season, usually from fogging.
At least he won't be working on my boat. Assuming a 4-tec burns ~8GPH that's equivalent to driving the 24MPG family sedan about 190MPH Of course the plugs will foul more often but that would be the least of worries.