Hi guys, newbie member fascinated by all of the info you guys make available. Thanks for the great site!
Here's my problem: I've got a '70 Mercury 500 w/Thunderbolt ignition. The first year I had it it ran great - just hummin along. However, the next year, I was unable to get out on the water at all, and then when I took it out the first time this year it fired up and ran, but just didn't seem to have any power. Seemed to idle a bit rough, but did idle, though when the throttle is put down could only get what feels like 1/3 power. Consulted with a mechanic friend of mine and proceeded to change plugs (not really fouled with the old ones), then drain fuel and replace with new mix and some fuel conditioner to help eliminate ethanol buildup, with experienced assistance checked the timing, throttle, choke, and cylinder compression, then most recently replaced fuel filter and older fuel lines between the filter and the motor which showed some minor cracking. All of these steps produced little or no result. The last time out a guy at the dock asked if I had a bad plug wire, so I started checking. When the #1 wire was pulled, the motor stalled, #2 still ran but very rough, # 3 similar to #2, but removing #4 seemed to have no effect. I could get a spark from the wire if it was right up next to a ground point, but it was no where near as strong as the spark from the other wires. The wire insulation appears in good shape and I cannot see a secondary spark happening anywhere along the wire. I've never really experienced an ignition problem that seems to manifest on only one point, but then my experience is all with automotive systems, so I'm not really sure how to proceed. Should I be looking for a new cap? Is there a rotor that can be worn? I haven't really torn into anything due to my lack of experience and the location of the distributor on this motor. It also appears that the plug wires are integral to the cap from my car experience. Is this correct and the wires are permanent with the cap or am I missing something on how to diconnect? If I do need a new cap & wires, am I looking for "vintage" aftermarket, or does someone still make something that is compatible with this distributor? Thanks for the help!