Melted spark plug?

[Neon]

Coming home the other night up the Greenhithe bridge (fairly cold) with the taps wide open and the bike drops a cylinder and loses power. I limp home and find the spark plug in no.3 cyl has fused contacts. Looking at the plug it has almost certainly leaned out causing the overheat, but I'm suspicious. Bike had 20k service a month ago including new plugs. They would have reset the mixture too / synched the carbs. When I pulled the other plugs out I'm pretty sure they weren't torqued up properly (I virtually didn't need the ratchet!) but they looked ok.

The question is, was it a random occurence (dicky plug) or a symptom of poor workmanship?

Would not torquing up the sparks properly cause an overheat?

Neon.

[JMemonic]

Id the plugs were loose it is possible that the cylinder was sucking air, not a hell of a lot but still it would mess up tje mixture.

Talk to who ever serviced it tell them what you found, the might see you right, btw be calm when you so this. Also never assume what has been done in the service ask for a detailed bill.

[CookMySock]

Its probably got too hot a range plug in it - what colour is the pipe?

Setting the idle mixture does little or nothing for full-power mixture. The cold night air will make the engine run leaner too.

Steve

[driftn]

I once had an R32 GTS-T Skyline that had a few mods. When I held my foot hard up it all the way to the red line in top, (which is very fast in a cage for the record) which I could only do twice before it would lean out so much it would burn the end right off one of the plugs (number 5 I think), Tried all sorts of different plugs and eventually it blew up big time. Moral is take it to the shop and get it looked at before it costs you a shit load of cash.

[Neon]

Talk to who ever serviced it tell them what you found, the might see you right, btw be calm when you so this. Also never assume what has been done in the service ask for a detailed bill.

Yep I think I will do that, and yes I have a detailed bill.

Its probably got too hot a range plug in it - what colour is the pipe?

Setting the idle mixture does little or nothing for full-power mixture. The cold night air will make the engine run leaner too.

Steve

Hmm it's a pretty standard plug I would have thought - MC41 engine from a CBR250. I figured the night air would have caused it to lean out, but still it has never happened before so suspect workmanship...

[YellowDog]

I would be pretty Pissed off if I were you.

Was it the Honda boys on Barrys Point Road?

[CookMySock]

Hmm it's a pretty standard plug I would have thought - MC41 engine from a CBR250. I figured the night air would have caused it to lean out, but still it has never happened before so suspect workmanship...

Theres no such thing as a standard plug. You use one plug, and its too hot, you put a slightly colder version of it in, or vice versa. Thats what the numbers on the plug mean.

Plugs don't have to be tight-tight. Just as long as they dont come out. There are more problems to be had from a too-tight plug, rather than a too-loose one. If a plug falls out coz its too loose, just wait for it to cool off and put it back with your fingers and put the lead back on it. it's not the end of the world.

It's nasty to inadvertently accuse someone of fucking your bike up before you have collected all the information. Take ALL the plugs out (number them left-to-right) and take a photo of inside the tailpipe so they can see the exhaust colour, and take it to the shop and show them, and ask nicely for their advice, and take care not to insult them or their workmanship, unless you have good sound cause to.

Steve

[Neon]

Thanks DB - I went back to the shop today and asked what might have caused it, they took one look at the plug and it's basically just not rated high enough for the punishment it was getting

They suggested I put an uprated plug in that cylinder so that if the mixture leans out a bit it can handle the heat ok. As for torque settings you are absolutely right - they are only nipped up and that's how they are meant to be. I learnt something today!

Thanks for the comments and advice.

[kiwi cowboy]

Thanks DB - I went back to the shop today and asked what might have caused it, they took one look at the plug and it's basically just not rated high enough for the punishment it was getting

They suggested I put an uprated plug in that cylinder so that if the mixture leans out a bit it can handle the heat ok. As for torque settings you are absolutely right - they are only nipped up and that's how they are meant to be. I learnt something today!

Thanks for the comments and advice.

not sure whot you mean by uprated but personaly i would not put different plugs in i would change all to the uprated

[CookMySock]

Thanks DB - I went back to the shop today and asked what might have caused it, they took one look at the plug and it's basically just not rated high enough for the punishment it was getting..

Good man. Just ask them to sell you a set of "colder" plugs for it, and you are away. "Hotter" plugs allow the electrode to heat up faster, so the bike is easier to warm up, but its also easier to overheat that electrode, and that is what has happened to yours. One range colder shouldn't make a huge difference, but chances are it doesn't idle so easily when cold. The heat range is the numeral in the plug "number". You want plugs with one number lower (I think) check this with them. You probably have an 8 or a 9 in it.

It might pay to get that exhaust colour looked it - it might actually be running too lean, or with too much ignition advance, meaning its something else altogether.

Steve

[quickbuck]

I would think you are darn lucky if you haven't put a hole in the top of your piston.
Yes, replace the whole set with one heat range colder.

[Neon]

What it had in it were '7's, they suggested going to '8s' (colder). I will take your advice and go for a full set. Funny because I've never had any trouble like this before, maybe it did have colder plugs before and I didn't know, I do recall it being very difficult to get started when just puttering around during winter last year.

DB my exhaust is a standard Honda job, it doesn't change colour at all that I can see! Am I missing something?

[CookMySock]

Funny because I've never had any trouble like this before, maybe it did have colder plugs before and I didn't know, I do recall it being very difficult to get started when just puttering around during winter last year.

This is what makes me wonder if something else is up. Something has changed.

DB my exhaust is a standard Honda job, it doesn't change colour at all that I can see! Am I missing something?

I mean down inside the tailpipe. The exhaust residue inside the pipe should be a nice medium-to-dark grey, not black, and not white. Take your bike to the shop, and tell them "some random bloke on the internet said you can look down the bikes exhaust pipe and tell if its running too lean or rich". It's not too critical, as long as its not really really white (too lean.)

Steve

[quickbuck]

Well, well, well... three holes in the ground.
Over the past 10 weeks I have removed quite a few plugs out of many bikes.
Mainly Bandits I must say.... Anyhow, none have been hotter than an 8.

This supports my (and DB's) theory that the plug was too hot....

Ask the shop what heat range of plugs they pulled out of your bike.

[CookMySock]

Its fair to put a hotter plug in the bike, for peoples who want to putt-putt around on it. It will warm up much quicker, be easier to start, less likely to stall, blah-di-blah.. in general, a better behaved engine. Different story for someone who wants to give it death.

Steve