Spark Plug Problems

[Guest]

What is causing my spark plugs to break down. I am running a Tohatsu 6hp outboard model 337A on my Trailer Sailer. Its an old motor (around 1986), however its in very good condition and normally starts first pull. Recently however I am having problems with spark plugs breaking down. With new plugs she runs perfectly, however after only a few hours running one plug will break down and she will then run on one cylinder. The plug will be wet but not excessively oiled up.
Usually cleaning will make no difference, when I fit a new plug all is well again, but only for a short time. Where is the problem likely to be, motor or plugs? I don't beleive it can be fuel related as I always mix it myself and take great care.

 

[BarryH]

I know it sounds a bit silly, but is the engine running the correct plugs, heat rating etc. If its only the one plug, are you sure the problem isn't further up the system. Such as the coils. These things can be a problem area. My old jap bikes of yesteryear would exhibit the same problems. The coil got warm and the resistance rose, the thing stopped working. Let it cool down and it was fine.

OK, to hell with it. Unbolt it and we'll use it as an anchor!

 

[Guest]

When I have the plug tested I am told it has broken down, and yes it appears to be mostly on the bottom cylinder.

 

[chippie]

Like the previous poster I recall similar problems on the early jap bikes.
By swapping the low tension leads on your coils and then the HT leads you could determine whether it is in fact coil related as the problem would shift to the other cylinder. Having said that, try changing the brand of plug and see where that gets you. I remember once having your sort of problems using champions and solving the problem by changing to NGK.

Good Luck

 

[andyball]

I'll second that about ngk plugs, I wouldn't use anything else in a 2-stroke.

 

[charles_reed]

If you have an in-line suppressor in the HT lead, it is probable that the supressor is at fault.
As suggested try changing the HT leads over and see the problem shifts to the other cylinder.
Or, replace the lead and see if the problem goes away.

 

[Col]

What colour is the good plug? If it is a bit on the black side, this suggests fuel /air mixture wrong. Because of uneven mixture distribution in manifold, it can cause 1 cyl to drop out before the other, if you see what I mean. A black plug has carbon build up, carbon conducts electricity, plug then shorts out and stops sparking, so then gets "wetted" by unburnt fuel.

<A target="_blank" HREF=http://www.arweb.co.uk/argallery/colspics> Cols Picture Album</A>