Burnt spark plug

[titaniumneck]

What would cause a spark plug to burn down/away the center electro. And the burn away the little arm that goes over the center electrod. 2 stroke 2 cylinder Tohatsu 40hp. When I say burnt the center electrod, I mean gone. But gotta give it to Tohatsu, it still was running top notch.

Mod EDIT: This is what mods are for. Report any problems, and we'll handle them. Singling out another member typically doesnt go well.​

 

[ondarvr]

Running lean, or the timing being off. Typically when the spark plug starts to be eaten away so is the top of the piston, which ends up as a hole.

 

[boobie]

Do a compression test on it.

 

[titaniumneck]

I will try the compression check next week. I don't know if this makes a difference but I just took this motor off a jon boat and put it on a 15ft sprint. Funny thing is it was faster on the sprint then the wide jon boat.

 

[titaniumneck]

I felled to mention that the spark plug was loose, could that have have done it. Could that have burnt the spark.

 

[Scott Danforth]

no, your most likely running lean.

check the compression, and look into the chamber at the piston

 

[Sea Rider]

Install 2 new plugs NGK BTHS 10 or BR THS-10 gaped tight to 1.0 mm, use OB for some time and check if both plugs are OK. Probably a faulty spark plug, which brand was and its heat range ? Time advance on those 40 HP is mechanical, impossible to miss fit by itself unless someone fingered it.

To check if within specs, with OB OFF put gear level to forward position, full throttle, check if carb's butterfly remains fully open and advance timing plate mark stops at 25? right in middle of both mating surfaces, If so, carb and advance timing are in perfect synch.

Which boat is lighter ?

Happy Boating

 

[wrench 3]

I felled to mention that the spark plug was loose, could that have have done it. Could that have burnt the spark.

The most common cause of a burnt spark plug is a loose spark plug. It can't transfer its heat to the cylinder head and over heats. As mentioned, on two strokes it usually melts a hole in the piston.

 

[titaniumneck]

Yes, Mr sea rider, I will go get a set of that size plug. And it is to the specs you stated. I just transferred that motor from a Xtra wide 56 inch jon boat, to the sprint. The sprint is a couple hundred pounds heavier, but at wot most of the boat is out of the water, so I figured the less drag made more speed, I guess. I also noticed when I got home the gas line plug was leaking gas. So if it's leaking gas not running, I guess it would be sucking air when running.

 

[Sea Rider]

When internal plug o'ring becomes dried, worn out OB fuel pump will suck air and OB miss. Unfortunately those o'rings are not available as spare parts which is a real crime. Will need to look for those at a car shop that sells o'rings.

Remove both sides with a thin pin and take to shop to match them, specify gasoline use. Light lube with olive oil once resting inside both female plugs, will slide as a charm on both male plugs and last longer.

Yep, less drag more speed...Didn't know that a loose plug on cylinder head could render a hole on piston besides screwing badly the electrode, never happened to me as always adjust tigh all spark plugs on head with proper wrench., you always learn something good.

Happy Boating