spark plug fix

[SIMPLEMAN]

boy is my face red.:o after trouble shooting for about an hour, switching coil packs around and what not, it appears that i have a spark plug that works sometimes and sometimes it doesn't. (i can't spell intermittent). it has always been for me a plug was either good or obviously bad. fouled,carbon flake in gap, cracked insulator,etc. this one........anyway, since i've had this problem, a lot of folks are telling me these four strokes do this. one guy said on his yammy he had to change them every fifty hours. i'll be changing mine every seventy five from now own if i keep this boat.Doh

[barus243]

I'd check the plug wires while working with troubleshooting. I wish you the best of luck at figuring out the miss.

[Rapala#1]

all the plugs or just one?

[SIMPLEMAN]

just one that was bad rap. but for eight bucks and some change, i'll replace them all.

[Rapala#1]

well, then at least you know its not the stater or the trigger, what brand of plugs have you been using, almost all boat engines need NGK plugs, for some reason other brands aren't quite right.

[ballistic lures]

Most use NGK because they have such a wide variety, so you can dial in alittle hotter plug or alittle colder plug.
Just have to watch out for the ones marked with an "R" thats a resistor plug you can pull it out plug on the plug wire ground it to the block and turn the motor over and it will fire, screw it back in and it wont fire under compression, Ive seen them do that too. My dads been a merc tech for almost 40yrs and I grew up around the shop and the marina seen some crazy stuff. I once saw an 70's model 50hp running backwards!

[gabowman]

Short story..........I carried my riding lawn mower to the shop a while back. Without the blades engaged it ran fine at high speed but everytime I engaged the blades it cut itself to half throttle. Thinking something was wrong with the deck I removed it, greased all fittings, went ahead and replaced a bad belt...but nothing really obviously bad. Anyway, put deck back on...same problem. So, after repairman charged me for fixing it he told me that one of the two sparkplugs was breaking down with a load on it and he replaced the inline fuel filter. I felt sorta foolish but like you, I thought the plugs were either alright or bad....no inbetween. I guess youre never too old to learn something new.