Boat and Auto spark plug observation.

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swampratt

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Do not know exactly how to title this but want everyone that chases no start or misfires to know some thing I found out 35+ years ago.

Just because a spark plug looks good does not mean it is.
Looks clean and worked before means nothing and just because it is new does not mean it is good.

My first was a leaking carburetor that fuel fouled some spark plugs.
Gal brought her car in the shop and this guy built the carb and changed plugs and sent her down the road and she made it less than 5 miles and it would not start.

Mechanic went to fix the car and called and said plugs look clean and it has fuel but will not start.
I told him remove all plugs and wire brush them or take a knife and scratch up the ground strap and center ground.
He did and it started and got it back to the shop.
Buddy got spark plugs for his Ford and just routine maintenance and after installing them the engine ideled terrible and threw codes for all 8 cylinders misfiring.

Pulled the plugs and noticed they rattled when you shook them. Oreilly stood behind them and got him fixed up with another set for free that did not rattle.
Fixed it.

Last Saturday I took the boat out and noticed it was a little rough at idle but give it throttle and it smoothed out.
Plug wire had fell off and I ran all day like that.

I hooked up the plug wire after looking at the spark plug and went out yesterday and takl about rough running that engine was missing and coughing and did not clean up at any rpm.
I took the dog house off and unplugged that wire and it smoother right up.

My buddy said you did not unplug a wire and make it run smooth as he was in the boat with me.
I said look at it as I had the doghouse off and running it across the cove.
He looked and said i would never believe it would run smoother with a wire pulled!

When I got to my spot i pulled the plug and it looked clean but I went ahead and scrapped the grounds with my knife and hooked it all back up.

Smooth running with all 3 cylinders hitting now no more misfiring.
This is a mercury marine plug that is flat so they are easy to see if they are dirty and it looked fine.

Fuel can create some kind of resin coating that will not allow a plug to fire.
Enjoy your day I must go fix my trailer hub that shucked the bearings on my pontoon on the way home from the lake yesterday.
 

wawazat

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Ha, rule of thumb for GA aircraft is that if you drop a plug it needs to be replaced. They are not cheap so I handle very carefully when I take them out every year at annual.
I use the same rule on my performance engines. It isnt worth the risk to fuel wash a cylinder over a spark plug. I also keep 8 plugs already gapped on the shelf. I do not keep any plugs in my shop that haven't been gapped to the specific engine they are intended for.
 

Shoot Summ

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Test ran my boat 2 weekends ago, it was missing after being stored for the winter. Thought it might be the fogging oil so ran it a while and ran the RPM's up to see if I could burn it off, no go. Picked up some plugs and changed them last weekend, probably 3-4 years on them at least, boat runs good now. Bad plug was only obvious because it was wet, other than that it was same color as the others, and appeared to be fine.
 

swampratt

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I have ran the same spark plugs in my 50hp mercury since 1982 and never fogged that engine.
But I never run the carbs out of fuel either and it is a 2 stroke.

I did an experiment with a 1982 Ford mustang with inline 6 200" engine.
I kept the original Motorcraft plugs in it until the car fell apart around the engine.
376,000 miles and got the same 27 mpg when I pulled the engine & trans and gave it to a friend.
I cleaned the plugs and regapped them when needed.

Front suspension from the mustang went under my 69 Camaro. Ford 9" went under it also.
Around 1998.
Now people put GM LS engines in those Mustangs.
 

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