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Old 02-02-2009, 03:37 AM   #1
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Default '05 Yamaha F250 Spark Plug

Went out to test newly tuned props yesterday, and noticed that starboard engine is not as responsive as port, and would not reach maximum RPM's. Also burning almost 2GPH more fuel than port at 4600 RPM. First thing that comes to mind is fouled plug. How difficult is it to change plugs in this engine. I removed plastic cowling off rear of engine, but came upon some sort of long plastic shield attached over what appeared might be spark plugs. Didn't go beyond there. Does this just pull off as a unit, and are special extensions and/or special spark plug sockets needed to remove and check plugs? Also, does sparkplug sound like a reasonable assumption?
Thanks,
Dan
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Old 02-03-2009, 05:03 AM   #2
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Default Re: '05 Yamaha F250 Spark Plug

This engine is equipped with coils mounted on the spark plugs which need to be removed before plugs can be accessed. A fouled spark plug will normally cause a very noticeably rough running engine at idle. It maybe time to run a combustion chamber cleaner through the engine. If the cleaner doesnt pickup the rpm have your dealer do a cylinder leakdown test.
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Old 02-03-2009, 02:29 PM   #3
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Default Re: '05 Yamaha F250 Spark Plug

Changed spark plugs last evening, and all existing plugs looked very similar, with tanned color, not too wet, etc. Electrodes were a little worn but not bad. Ran boat this morning, and starboard engine is still not attaining max RPM and is definitely burning almost two gallons more per hour in the mid 4000's RPM range. Otherwise, engine is running every bit as smooth as port engine.
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