Mercury outboard question

[lumberdude]

Okay, after some sort of computer glich, I'll try posting this question again...<br /><br />I've got a 1970 Mercury 200 20hp outboard with what I think is some sort of electrical problem. It starts easy, idles okay, and if the plugs have been freshly cleaned, both cylinders run great. After a few minutes and some cycleing between full speed and trolling speed, the bottom cylinder drops out completely. If that plugwire is removed and plugged back on, it will fire sporadically. The plug is obviously fouling at this point, because if I remove it and clean it, it will give me another 10 or 15 minutes before it drops out again.<br /><br />My marine dealer tells me he has replaced one coil and the points, and cleaned and adjusted the carburetor. I'm not sure if he has tried replacing the plugs or the wires. The plugs it has in it are NGK brand and are the modern ones that only have a center post and the spark travels from the outside of the plug to that center post. It has been suggested that these plugs require too much voltage for this motor.<br /><br />Does anyone know of the manufacturers recommendations for what plug to use?<br /><br />Any ideas out there as to what could be the cause? My marine dealer seems to be at a loss as to what the answer is.<br /><br />

<br /><br />Thanks<br /><br />Kory

 

[KCLOST]

Re: Mercury outboard question

lumberdude,<br /><br />You probably don't want to hear this but I can't help it.... Get out the owner's manual. IF you don't have one, call up Mercury and get one. It's possible that you may be able to get the info on plugs for your motor off the web also....<br /><br />Don't let yourself or the idiot who doesn't know what the problem is, drain more money out of you...<br />BTW, check the compression's in the cylinders against spec. <br />Also, take the cowling's off and hook up the rabbit ears, run it at night to see if you see any arching across the plug wires or anything else... This is something you can do easily to see if there is a wiring problem....

 

[peek]

Re: Mercury outboard question

Hi I have that same old Motor setting up for parts...but the plugs for it are Champion ..J8C..

 

[tmcalavy]

Re: Mercury outboard question

The Old Outboard Book lists Champion J6J plugs for Merc 200's ...pre electronic ignition anyway. Can' t tell from the pic, but your outboard looks like a redband? which would make it pre electronic ignition. Those surface gap NGK's need more juice. Check for spark at night like the other post suggests. Then put the Champions in and check for a good hot spark with these plugs (pull plug out, connect plug wire, hold plug end close to side of engine while someone turns the flywheel). If you don't get a good hot, blue spark on both, swap the coils. If the weak or no spark condition moves with the coils, you need a need a new coil. Good luck.