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'Twas the plugs (I hope!). Hmmm...

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by mattb, Mar 17, 2010.

  1. The Hornet has run badly a few times in the last week, when cold. Like it's starving, or running on 3 only cylinders. I've ignored it, but commuting somewhere and back yesterday morning, it was bad the whole way.

    So I decided to start by replacing the plugs. This takes about one minute on the SR500 and about one hour on the Hornet! :? Plug one, then two, looked fine at the tip. Except that had liquid (water, petrol or oil, or some combination? Didn't smell distinctive) on the threads. Especially on number two, which is second from the right, below. But number three (second from left) was fouled. I'd say three wasn't firing properly (a cause, or a consequence, of the fouling...hmmm?). The fouling was a dry or lumpy-goo like oil. I'm hoping it was a faulty plug that was the cause - the bike runs fine now. Of course it could be a fault causing a good plug not to fire properly. I bought the bike 13,000km back and a few months ago. It had recently had a major (40,000km) service, which involved untruths (they claimed to replace the brake fluid, which they didn't as the RWC test showed). Not sure if they mentions doing plugs. Number three is such a pain to remove, maybe they skipped it, and the plug is just old (or maybe they didn't do the plugs in that service, and they're old).

    Spark plug one and two (moving from right to left) connect to different coils (of which there are two). I can't remember whether plug number one shares its coil with number three, or four. It would be interesting if it is the former - one and three sharing a coil - as their insulators are both black, whereas two and four are white with nice tanned tips. One's tip is mildly ugly, so if it is attached to the coil feeding the fouled number three it might warrant inspection of that coil and its wiring.

    Any suggestions for my musings? I wonder what that liquid might be on the threads?


  2. coils will be 1-4 and 2-3.

    I hope plug 2 doesn't mean a cracked head. Might have been just rocket cover gasket leak into the plug recess. That could explain all your problems.

    there is some weird stuff going on with your tips however.
  3. Just browsed a U.K. Hornet forum and somebody asked about this 'oil' on their threads, and a few people commented that they put oil on their threads when putting them in. Might explain things, esp given there is not much on, and it's at the base of, 1,3, and 4. The funny thing is number 3, the fouled one, has the least oil on the thread, so it seems unlikely it was fouled by a leak. Hopefully my 'old plugs' theory is true. And hopefully it is just a gasket leak and no 2.

    Oh, I've strayed from the path of air-cooled, agricultural, simplicity and feel. In a few months time I'm going back to a big single or twin...just serve me faithfully till then, Bettsy (or I'll beat you).

    The difference in tips certainly is strange....
  4. Ahh the oil on the thread makes sence.

    Also looking at the tips, I've seen something similar before, but worse, in that the 1-4, 2-3 common coil will favour one of the two plugs if the resistance isn't right.

    In your case 2 is firing in lieu of 3 and 4 is firing in lieu of 1.

    In my case it was barely firing on one cylinder and I had it on two separate occasions. Once because I had non-R type plugs in, the second because I had a plug cap break down.

    I note you do have R type plugs, still double check they are the right plugs. The reason I had non-R type plugs was because the NGK catalogue listed them incorrectly.

    Then check your cap resistance. There will be a value in the manual.

    Still I can't believe how clean those two plugs look without having "lean errosion". This may suggest carb(?) imbalance, but I doubt it.
  5. Some really helpful advice there, thanks. Interestingly, the idle sounds as though the carbs are out of balance.... The plugs are right as per the manual; I'll next check out the resistances.

    The rubber for cap one was split in half all the way, top to bottom, and not fully sealing the cap recess from rain - I wonder if this is also related to my bad running in heavy rain (or maybe that was plug three, running badly in the wet as in the cold, through some electrical fault which those conditions activated or worsened....)
  6. Plug 3 looks really old and worn, even the flat tip is worn compared to the others.
  7. As long as you've got them out, get yourself some Iridium plugs; expensive but they last forever, and definitely improve the performance and economy....
  8. Putting a little bit of oil, on the threads, before installation, is a very good practice
  9. Well I took the bike out for a decent spin today, to Eildon National Park, and even got stuck in a quite heavy downpour all the way back through the Black Spur, and the bike was fine - hopefully old age was the problem! I wasn't sure what a worn plug looked like (they don't last that long in the SR500), glad to have my theory (or rather, my hope) confirmed.

    Hornet, I went and bought a spare plug in Healesville, just in case I needed to do some roadside self-assistance. When they charged me $8 for one, I thought: Damn, should have got iridium plugs in Melbourne!

    It's funny how what keep seeming threatening to be big problems, turn out to be nothing but old plugs, blown fuses and blown globes.... Even the recent head bearing replacement was not that hard, in hindsight.
  10. In my fairly extensive experience of grotty old bikes, small but niggling electrical and fuelling faults can detract from the riding experience far more than even quite major mechanical issues. Which is a good thing really as they are often simple and cheap to fix, and you end up with what can feel like a new bike.

    As an extension of this, although I've had some fairly major blow-ups, most bikes (vehicles in general for that matter) that actually come to an unscheduled stop, do so as a result of a broken wire, a grubby electrical connection or a barely visible speck of muck in a carb drilling. Coming to a halt at the end of a long, wiggly black line or a trail of smoking oil and incandescent aluminium is, mercifully, rare, but it does make for a better story :grin:.
  11. It IS funny that modern bikes are so reliable. I guess it's the product of years of research and trial and error, but, compared to the number of cars you see broken down on the side of the road, the number of bikes is miniscule (oh, except Harleys, of course).
  12. Modern Harleys are quite reliable.
  13. MAybe so, but you still see 'em stuck by the side of the road pretty regularly.
  14. i don't. Maybe I need to move somewhere else
  15. To resurrect this post:

    So plug number three stopped firing again this last week! 7000km later. Pulled it out and it was wet with fuel, and a tiny bit of oil (enough to foul it, then get covered in petrol?). Aarrgh. Haven't ridden the bike properly since but the bad running - on three pots - was gone on the test ride. So, it seems maybe there's an oil leak there.... I'll see how I go, and if the problem returns, I guess the next step is to go one degree hotter on that plug....
  16. Wet with fuel suggest not firing or firing very weakly OR a carb problem...ie stuck float needle, blocked / badly adjusted air compensator ( idle jet), badly worn emulsion tubes.

    Back to the ignition related thoughts....

    Q. Have you checked the quality of the spark on that cylinder?

    Q. Are the coil packs identical? ie. same shape, size, wires, etc

    Either beg, borrow steal a coil pack and replace the one driving the fouling plug, or swap the ones you have.

    If swapping them shifts the problem, or if a borrowed one solves the problem......

    Check / replace the plug lead on that cylinder...looking for any sign of rubbing, burning etc...

    You could also do the best thing possible for a honda...burn it.
  17. Wot Mike said.

    Also, never assume the health of an NGK plug. I've had enough that were dud straight from the box to remain suspicious at all times.