proper plug wires

[jeffreyk573]

I have some pretty thin looking plug wires on my Saltare. These wires are brand new. Installed by a marine mechanic when he replaced the Pro Tec ignition system on my boat this winter with a Prestolite marine distributor.
I had some beefy looking PCM spark Plug wires on it before the conversion. I also have a pretty good miss after the boat gets good and warm. The miss is worse when under load. Runs great at idle, and starts right up at the turn of the key. I'm a little perplexed, and would welcome any suggestions.

[michael hunter]

The standard ign wires are 7mm high energy ign wires are 8mm they will look much bigger.
There are many reasons for a misfire . One easy way to check the wires for insulation breakdown is to spray water on the distributor ,wires and coil then look for sparks or misfires. Use a spray bottle for this. Skidim sells PCM branded wires.

[cadunkle]

I just replaced my wires with Mallory Marine 8mm wires and they are fine. I've used Mallory Marine ignition parts in the past and will continue to use them as my first choice, just seems like good quality with no issues.

[jeffreyk573]

The plug wires that my mech replaced were PCM branded wires that were brand new. The boat had never ran on them. I bought them from DIM for the Pro Tec ignition system. Would they work for a regular distributor. The installed wires are also just a jumbled mess running everywhere. Can a plug wire cross fire? And could my miss be attributed to the wires getting hot near the engine, or maybe just one or two wires are doing this. We have actually still been able to use the boat, just with a miss. Sorry if the questions are dumb, working on this boat is about the only engine experience that I have.
It's not really my forte. But I like the boat.

[cadunkle]

Wires can crossfire On small block Fords with the early firing order this is common on #7 and #8 as they are right next to each other and fire one after the other. Not sure on a BBC which might be more likely to be trouble. My new wires are just hanging under the exhaust but are a good fit so aren't hanging on the stringers or stretched, actually not too messy for no clips on them. You do want to keep them off the exhaust though, at least the primaries on the manifold which are not water cooled and get quite hot.

I'd double check the firing order and failing that, the plug gap and that no insulators were cracke during install... It happens sometimes and you might not notice when tightening. Also check voltage at the coil. If the coil was made for full 12v be sure it's getting that and not going through a resistor dropping the voltage or spark will be weak.

Is the miss just at idle or is it at all RPM?

[jeffreyk573]

There is no perceptible miss at idle. It starts at about 1500rpm and continues throughout the rest of the rpm range maybe a little bit worse around 3000 though. And the engine runs great at all rpm for the first 10 to 15 min until everything gets good and warm, then its a slight miss, that gets progressively worse.

[ngavchris]

If you have the new ignition installed. Remove the rubber gasket off the distributor cap and see if that cures the problem. My brother had the same issue with his and we tried a new cap. Still didn't work. Turns out the new ignition sits a little lower than those with points. Runs like a champ now.