Mercury 500 Strange Ignition Problem?

RickG79

Cadet
Joined
Dec 12, 2020
Messages
13
Update. Haven't had much time to mess with engine so I swapped out plug wires and went fishing. It appears cylinders 1 and 2 have problems as engine will idle but won't rev up past about 2500rpm. They are wet with fuel though so they definitely are getting gas but not firing right. Time to retest entire ignition as I'm reading this could be stator, trigger, or power pack? I don't want to buy anything unnecessary. Need to find spark tester and multimeter and check everything again.
 

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Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,934
switchbox or stator. flip red and blue wires if problem stay on 1 an 2 its box.
 
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RickG79

Cadet
Joined
Dec 12, 2020
Messages
13
Update, better late than never! Long story short I took all of your advice and went out troubleshooting with a spark checker, timing light, and CDI manual. Spark on and 1 and 2 could not jump 1/2" gap, it was faint. 3 and 4 could jump gap. Interestingly, timing light showed some flashes on all 4 but was sporadic. A dva adapter showed good voltages cranking on trigger and stator so this lead me to switchbox. Me being a cheapskate I went with the $20 Amazon one instead of the $400 Mercury one.

I started wiring it up and when I got to the last damn wire it sparked a couple times....forgot to disconnect the battery. I tried it anyway and same thing, poor idle and only firing on two cylinders.

I ordered another switchbox and Boom, strong spark on all 4 (remembered to disconnect battery this time). I even heard this mysterious "snapping" sound to describe good spark that I've read on other posts. So, either I fried that first box by accident, or it was bad out of the box. I haven't lake tested but in a barrel the little engine sounds like a beast. Smooth idle now, no stumbling at all or obvious misfires. Thanks to everyone that responded to my post.
 

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