Best spark plug against fouling 1990 Evinrude 4hp.

cprodave

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My Evinrude E4RESR has some degree of fouling that I would like to take preventive action against. Engine has been running Champion QL77JC4. I also see Optional plugs listed are QL86C or NGK BZ7HS-10.

What is a good (slightly hotter) sparkplug to replace the QL77JC4? I would think next hotter is QL77JC6. Or L77JC6 ( I don't need the "Quiet")? Or could I use NGK BZ6HS-10?

Any input will be much appreciated...
 

racerone

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Fouling is much ---" mis- understood "----Just use the factory recommended plug.
 

cprodave

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Ok, subsequent to initiating this thread I found another thread that went into great detail and concluded exactly what you are saying.

Thanks
 

Sea Rider

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Spark plug fouling is very notorious on 2 stroke motors, whichever HP they are. It's all about plugs not reaching their self cleaning temp which is achieved at + 500º C. Trolling motors will go that way, can install a next higher spark plug range, but will go that route. If a trolling motor will be used for that specific purpose, that's running at idle or fast idle rpm speed can use 100:1 fuel/oil ratio, but remember not to exceed those mentioned throttle settings or risk screwing the motor due to poor lubrication at higher rpm.

Happy Boating
 

cprodave

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SeaRider ,thanks for this input. I have read similar recommendation from Leeroy's Ramblings except Leeroy advises Full Synthetic oil at 75:1. I suppose Leeroy's method provides somewhat better protection than 100:1 if occasionally operating at faster than trolling RPM's.

I agree with other inputs stating that fouling is a symptom of deeper RootCause/Fix other than going to a hotter plug. I wasn't aware that 500degrees achieves self-cleaning. That is good to know and takes some of the mystery out re: ideal combustion.

Working on this motor a bit yesterday I discovered a new condition/concern (motor "binding up" slightly at 2 rotational positions) so I will start a new Thread on that. Thanks again.
 

racerone

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Would this slight ---" binding "----Have anything to do with flywheel magnets ??????
 

kbait

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You have electronic ignition, which normally produces strong consistent spark. Make sure the coil grounds and ground from cd box are clean/tight. If you troll/idle a lot, you could open plug gap to .35” (.30” is factory spec). Fuel mix at 50/1..
 

oldboat1

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I ran mine with the recommended oem plugs and gap, 50:1 mix -- always tried to clean it out a little running back to the dock. Easy motor to maintain.
 

cprodave

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Yes it was rusty flywheel magnets (please see other Topic for update--now chasing a Fuel problem).

Thanks.
 
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