1985 Merc 75 ignition wire arcing

[n ferrazza]

I'd appreciate any ideas, as I am stumped. It's a 4 cyl., no distributor. I am losing 1000 rpm's and power through all ranges. I've tested compression-all in the 170's. Fuel system incl. carb's are fine. I've replaced high tension wires, connector's, and boots, yet the wires are arcing through the insulation. Most heavy on cyl. 3 and 4. The arc's are heavier near the coil's, and will arc to the block or anything connected to it. <br /><br />All cylinders fire. Plugs are fine. I do not have equip. to test coil's and switchbox. They are obviously working. Could I have a major short somewhere with the arcing going to the wires from the block? Is it possible that the stator, which visually looks fine, is outputing way too much power? But wouldn't that fry the switchbox or other component's? <br /><br />Thanks

 

[Dunaruna]

Re: 1985 Merc 75 ignition wire arcing

Hey Nick,<br /><br />If you spark plugs are faulty the high voltage will look for (and often find) the easiest path to ground, we see that as arching. Also faulty or poor quality wires will do the same.<br /><br />Use a water hose as an analogy, a blockage or leak will reduce the water pressure at the exit point.<br /><br />Aldo

 

[DHPMARINE]

Re: 1985 Merc 75 ignition wire arcing

Nick I am far from being a Merc pro,but 170 psi is extreme.New motor probably isn't that high.<br />Could you have carbon build up and the plugs can't fire under that compression?<br />DHP

 

[n ferrazza]

Re: 1985 Merc 75 ignition wire arcing

Thanks Dunaruna and DHP:<br />The new ignition wires are from Merc Dealer and the plugs are good. I've tested each one. I suspected my compression was quite high, unfortunately my Clymer shop manual doesn't specify, except that the compression in the cylinders be within 10% which they are.<br /><br />But it is almost a certainty that I have alot of carbon build up. I bought the motor new in 1985, and I have never decarbed it. I have a can of SeaFoam waiting to be used. I will try it.<br /><br />I wasn't aware that excessively high compression could cause the plugs to misfire. And for as much voltage as <br />it seems to generate, my plugs are partially fouling. Thanks, I'll post the results of decarbing.<br /><br />Nick