Re: 2-stroke vs 4-stroke spark plugs;am I dreaming

[rvpapasso]

I started this thread and now I will tell you why. I have been trying to solve hard start issues with a friend’s 1962 Evinrude 40Hp for the last 3 weeks. Engine starts great when cold with choke, idles all day, throttle transitions smoothly and has a great top end. However if shut down and it will not restart until almost dead cold.

I replaced the magento’s, spark plug wires, spark plugs, grounded the magneto plate to the block and swapped out the ATOM ignition modules with a new set. The float is good and the float needle is not leaking. The temperature gauge (also measured with a thermocouple and DVM on the head) indicate the engine is not overheating. The plugs are NGK B8S and the insulator is tan when I remove them. This really had me stumped.

On the last trial run the engine ran sweet thru high speed and no wake zones about 45 minutes down river. We shut it down, drifted for about 10 minutes and it would not restart (it is electric start). Fortunately we drifted to a dock and I did some diagnostics. The plugs were slightly wet and I noticed they were side arcing. We did not have a clean set of spark plugs or sand paper (I still am kicking myself for not checking my buddy’s tool kit!) but had a metal file. I took the file and filed the sides of the side electrode clean and around the center electrode. Put the same plugs back in and it fired right up within 1 turn of the flywheel.

With that we headed back to the marina where we put in at. Once shut down the engine refused to start again. That’s when it dawned on me about the old Champion J6J with the center electrode cut back. Next weekend we pulled the SAME spark plugs and with a Dremel tool cut back the center electrode.

The engine started 10 out of 10 times, hot or cold, anytime the starter was engaged. No continuous cranking, just a quick blip on the starter switch and it was running. We shut it down for 2 minutes, 30 minutes and even 1 hour with the exact same results.

My best theory is the plugs were wet fouling when the engine was shut off and winding down still pulling fuel into the cylinders. The starter spins healthy but at low cranking speed the mags maybe were not generating enough energy to blast through the wet electrodes. By having a sharp edge from the side electrode over the middle of the center electrode, the edge doesn’t get as wet and electrons flow better from a sharp edge than a flat surface (aka lightning rods) and that edge is right over the center electrode for the spark to jump. It was like magic!

I am sure there are going to be many theories as to why this made a significant difference and what the real problem may be. I am just reporting the results and I am sure there was some engineer at OMC or Champion that had good reasons to make the J6J with the center electrode cut back. For now it was the magic bullet for his engine.