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Spark Plug Not Firing Question

  • Thread starter Thread starter Suzuki_Don
  • Start date Start date
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Suzuki_Don

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My GS550B was missing the other night and I worked out that one cylinder was not firing. No. 2 cylinder exhaust was cold and the other three were really hot. When I removed that plug wire while the motor was running obviously there was no drop in revs. I removed the spark plug, attached the plug lead to it and laid it in the cylinder head and started the motor. There was no spark as I had suspected. When I lifted the spark plug off the cylinder head by about 1/8" a big spark jumped from the hexagon part of the plug (earth) to the cylinder head and a nice fat spark jumped across the spark plug points. When I put the spark plug back on the head, WHALLAH no spark at the points of the plug. can someone tell me what is going on here and why a plug behaves in this way.


Cheers

Don
 
what's the cable like for that particular sparkplug?
change the sparkplug and see what happens?
 
Plug is dead; no spark with plug grounded but sparks when plug is lifted off engine. Try a new plug and see what you get.
 
New plug works fine. I am still puzzled by the symptoms of the old plug though.

Don
 
Plugs wear out. It happens. Could be anything from the porcelain to the electrode. Don't worry to much about it.
 
Don, its not unheard of for them to come from the factory being bad. Ive had a couple instances where a car i would be working on would be missing, and i would trace everything i could think of and it ended up being a stupid BRAND NEW plug...it happens. If you're good to go now, and you checked your fire everwhere and found nothing, i wouldn't dwell on it too much.
 
Carbon is also conductive and a piece could maybe got stuck somewhere and short the gap, if it was not a factory fault.
I recall a trick when I was in school, someone would take a pencil and draw a thick graphite line from the top of your bikes plug down to the base and put the plug cap back on and the bike would be very difficult to start and sometimes pushed home. A thin single strand from a multicore piece of wire works perfectly and stranded a rider very quickly, especially if he was a bit forward about his new bike etc!
 
Matchless said:
Carbon is also conductive and a piece could maybe got stuck somewhere and short the gap, if it was not a factory fault.
I recall a trick when I was in school, someone would take a pencil and draw a thick graphite line from the top of your bikes plug down to the base and put the plug cap back on and the bike would be very difficult to start and sometimes pushed home. A thin single strand from a multicore piece of wire works perfectly and stranded a rider very quickly, especially if he was a bit forward about his new bike etc!
Click to expand...

We used to do the same trick on the village policeman's CB200 Honda - many's the time we watched him riding on one cylinder and he probably hadn't even noticed!

Wally
 
When the charge travels down to the center electrode on the plug it doesn't jump across the gap immediately. It builds up for a bit and then jumps. If the charge can leak off to ground as it gets to the plug it will and not fire. When you remove the plug from the head and hold it away from the engine the charge gets blocked from ground and has to build up to arc. Some have found bad plugs by pulling the connector in the cap just off the tip of the plug creating a gap there that will allow the plug to fire.

Oh! By the Way! If you look at the coil you'll see that each one fires two plugs. If both the wires don't have a patch to ground when the enige is running back currents can fry your coils and other ignition components.
 
Guess I wouldn't be so quick to not worry about it. Could be just a bad plug. It does happen. Hopefully that's all it is.
But as was stated, deposits can be conductive and can 'short out' the plug. If there is something else wrong causing deposits, carbon or otherwise, to build up, it will just happen again.
Recommend you check the plug regularly for a few hundred miles to see if you might be running rich, leaking oil, intermittent ignition, etc.
Also, almost done with your manual.
 
Thanx Tomm for your comments. Will keep a check on the spark plug. I put a new one in and the motor is now running fine. Pulls 9 1/2 with no probs. Thanks for the effort on scanning the manual for me.
Cheers
Don
 
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