Broken spark plugs

[stubble]

Tracking my 2017 390, about 2500 miles on it. I had a head gasket issue that showed up as a stalled engine, pulled the plug (original) and the electrode arm had broken off. The bike had been overheating a couple times and using some water.

New plug and the bike would run but there was water in the exhaust so I pulled the motor and replaced the head gasket.I did not skim the surfaces. Put it back together with the same plug and went racing. Ran great- set a PB. But it lasted a day then lost power at high revs. Pulled the plug and it’s broken again!

This time there are no signs of head gasket issues otherwise. Leakdown test seems good. (about 1-2% lower reading on the motor side.)

what would you do now? What would cause the plug to break? Its a stock engine with stock gaskets and this new plug is an NGK non-iridium.

 

[kostean]

It is not broken off but instead looks melted off as it would in a severe case of engine detonation occurring.

 

[1JZSupra]

Looks like a detonation to me. What are your mods and are you tuned?

 

[Superpacman13]

Poor tune making detonation or the water is causing detonation. Either way its a big problem!

 

[stubble]

Thanks all for the replies. A little more info: The bike has a Tyga serpent exhaust, open airbox, and a PC5 with the corresponding map installed from this forum. Otherwise motor is stock. I have not had it dyno tuned. It had overheated a couple of times before I upgraded to the SPAL fan and new radiator cap, and I think this is where the original head gasket started its demise. When the head gasket went, it was clear: Water in the exhaust and visible pulsing in the radiator water.

After replacing the HG, I ran it for one track day. I didn't notice any detonation (I think I would?) and the temp gauge seemed normal (hot but not overheating). But this is when the second plug burned up.

I have two newer pieces of information since my first post:
1. When I put a new plug in it to fire it up, it did seem to run fine but the exhaust header got real hot real fast. It was visibly red within a minute of startup at idle. I don't think that's normal.
2. I believe I failed to connect the upper breather hose on the valve cover when putting the bike back together the first time. This hose goes to the airbox, between the filter and the throttle body. Would this create enough of an air leak to run lean and burn up my plug?

If not I think the next step is to redo the head gasket. Thanks for your inputs.

 

[kostean]

If you are cooking the exhaust red hot and burn plugs then probably the engine runs extremely lean. Remove PC5- if you are not exactly sure what AFR the map produces and have just installed it, the fault may be in there as it would be hard to explain running that lean just because of some unplugged hoses.

 

[stubble]

Thanks. Yeah I wasn’t sure whether thet line would lean it out given its on the ‘outside’ of the throttle body. FWIW it has been the same map since I got the bike 2k miles ago. I verified it against the map on the forum this weekend just to be sure it was still programmed. Not that it couldn’t be a faulty unit of course.

 

[1JZSupra]

Mind sending me a copy of that map so I can look at it?

rhoads.christopher.r@ Gmail

 

[390tyganiels]

Thanks. Yeah I wasn’t sure whether thet line would lean it out given its on the ‘outside’ of the throttle body. FWIW it has been the same map since I got the bike 2k miles ago. I verified it against the map on the forum this weekend just to be sure it was still programmed. Not that it couldn’t be a faulty unit of course.

Hi, did the issue end up being the hose. Or was it something else. I have the exact same problem on my rc. Burning up a brand new plug. Also a track based rc390

 

[ESPEC]

Hi, did the issue end up being the hose. Or was it something else. I have the exact same problem on my rc. Burning up a brand new plug. Also a track based rc390

Any updates on this spark plug tip broken off? I have the same issue

 

[1JZSupra]

Do you guys have some kind of fuel tuning?

 

[ESPEC]

Do you guys have some kind of fuel tuning?

Mine is a stock ECU
Replaced spark plug but
It has spark, has Fuel, it cranks but doesn’t start.