Mercury 6hp Two Stoke Issue

[svenskflicka]

Originally Posted by GILow

Also, how many turns of the idle mix screw did it need to reset the screw completely and how many turns did you back it off to get it running?

And one more thing, faulty HT leads seem to reveal themselves more often when the mix is lean, in my experience. No idea why, but I’ve seen it a lot over time.

Thanks for the replies. The low speed mix screw is set at 1.5 turns. I didn't get it onto the dinghy to do the adjustment properly (in forward gear). So I'll do the fine tuning when the dinghy goes in.

Oddly enough the sparking sound goes away when I juice up the throttle a tiny bit? How could that even be?

[GILow]

I am not surprised the HT leak goes away at higher revs, I’ve often observed the same in old cars. Something to do with the changes inside the combustion chamber reducing the resistance to the spark jumping the gap. There’s probably a description of the effect somewhere on the web. I’ll have a look.

But in the meantime, you have to find (and fix) that HT leak because it will get worse and eventually will stop that cylinder from firing at all.

[GILow]

This from an article in Wikipedia on “wasted spark” engines, indicated there are significant changes in resistance to the spark jumping the gap of the spark plug depending on what is going on in the combustion chamber.

“In a typical engine, it requires only about 2–3 kV to fire the cylinder on its exhaust stroke. The remaining coil energy is available to fire the spark plug in the cylinder on its compression stroke (typically about 8 to 12 kV).”

Of course it is not describing the situation you are in but it shows how much things can change in the engine cycle.

[Mo Surprises]

I too had a Merc 9.9 two stroke and foolishly sold it. One of the best outboards I have owned.

Don’t overlook the simple things. I solved my idling problems simply by increasing the spark plug gap to something like .040”. It was a couple years ago so I may be off a bit but I clearly remember that small adjustment making a tremendous difference.