TOPIC: merc 500 missing

Swapped out the mag from my 450 after cleaning and plugs no change

Boat looks good

May not be the mag. To test it take four old plugs and cut the side electrodes off to give the mag a harder time. Ground the plugs with the wires attached and give the engine a spin while observing the plugs. A good blue audible spark should occur each revolution, as a healthy mag should be able to give a spark a half inch long. No or weak spark on one wire but good on others is either a bad cap, bad wires, or a poor connection in the boots or cap. I replace the wires no matter how good they look, with new copper core stranded and add new boot springs as well, they cost peanuts. Spark is good? Examine the plugs for water droplets which mean a bad or cracked exhaust divider plate or a if the lower plug is wet with water, bad lower crank seals. More issues rather than bad spark will cause a miss.

Thanks for the help, I pulled the plugs and man did they look bad, will have to post a picture, one had some junk all the way over. Once I listened to some videos of other 500s run mine didn't sound like it was missing since both mags sounded the same. Well left the replacement mag on, I was going by the PO that there was a miss problem, said he had an outboard mech checking it, WELL never trust words, took it out for the first time on the lake and ran like a breeze and starts great. Didn't try WOT yet, just putting some time on it before I take the crop to it boat and Merc.

Very good.The 500 Super Thunderbolt is a top engine in the vintage Merc line up and is without par in my opinion. How the Hell should I know? Well, I own twelve of them from the Thunderbolt family, from a 1955 Mark 55 to a 1967 500 and all years in between. The 40 cube engines are known as Thunderbolts, and the larger 44 cube is called a Super Thunderbolt, both have the same DNA.

this is one of my super thunderbolts 63MPH.
NOT ME IN PIC.

two more 500's on a rare 16 ft Prywing hope to finish this spring.

I have a 'few' too
doc

That is one bad boat and I love the motors too, I have a Merc 950 SS but it's so heavy and my boats I think are too small.

I need a road trip to get some more, twins will just look too cool on the Wacanda.

What spark plugs do you guys use on the 450/500 NGK B6S?

Champion J6C (stock # 823) plugs work well and are inexpensive & readily available.

According to crossover charts, NGK B6S is the equivalent plug. They work well in these motors, too.

I've used Autolite 354 in the past and they did fine. Many times can be found dirt-cheap.

HTH..........ed

Thanks, a couple bucks each is cheap insurance.