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Plug cap questions

  • Thread starter Thread starter maclariz
  • Start date Start date
M

maclariz

Guest
Have some misfire issues on the GS400, it's always the right hand cylinder. I had a charging problem on yesterday's test ride (a connector on the red live line fell apart as it turned out) and as the battery ran down the misfire got worse until close to home it completely stopped firing on the right and I limped home on one cylinder. I just came by the idea that the misfire might be an issue on the HT since it seemed to be so strongly affected by the electrics. I just tested the spark plug caps and the results are as follows:

Left hand cylinder (fires without trouble): 4.6 k Ohms
Right hand cylinder (troublesome): 5.4 k Ohms

Should I replace? I assume the mismatch in resistance is a bad idea. Anything to watch out for when replacing them? Any particular type or brand to buy (the current ones are NGK, but they look rather old)? What should the resistance be? Can't find any information about this specification in my Clymer manual.
 
plug caps

plug caps

I don't think the difference in resistance you measured is significant. I had a similar problem with my GS450T and the problem was coils. I found a local shop that tested each coil under load and one did not provide any spark, and the other would only put out a spark for a very small gap. I had checked coil resistances with an ohm meter on both the primary and secondary circuits and they were within specs. The problems only occurred on the secondary side when the high voltage spark shorted to ground within the coil body. I had been having intermittant problems for several weeks with spark on both cylinders. My lesson learned - have coils tested under load on a coil tester.
DickV
 
I wouldnt waste my time testing and troubleshooting the spark plug caps. Just change them. Cheap and easy. Cut off the old caps to get at some clean wire and screw the new caps on. NGK caps are fine. If that dont help then go to the coils. Get some new spark plugs too.

Good luck...
 
bonanzadave said:
I wouldnt waste my time testing and troubleshooting the spark plug caps. Just change them. Cheap and easy. Cut off the old caps to get at some clean wire and screw the new caps on. NGK caps are fine. If that dont help then go to the coils. Get some new spark plugs too.

Good luck...
Click to expand...
The plugs are newish, I fitted them (in place of two non-matching plugs fitted by a previous owner!), and the bike has done less than 50 miles since then. May try to get some new plug caps anyway. But, in line with recommendations, I probably need to find some new coils without breaking the bank (original Suzuki ones seem likely to cost more than ?100), see my contribution to this thread.
 
Not to be troublesome but are you sure the problem is ignition and not a carb? A leaned out carb caused by blockage will look like and ignition problem, maybe the PO was trying to compensate with different plugs. GS bikes are known for carb issues (as any 30 year old machine would be) so I would replace ignition parts with known good ones and if it persists your next step is the carb block.
 
First thing to do is make sure the battey is fully charged. Dead battery will cause it to miss. New plug caps wouldn't be a bad idea, get NGK caps
$3-4 @
 
duaneage said:
Not to be troublesome but are you sure the problem is ignition and not a carb? A leaned out carb caused by blockage will look like and ignition problem, maybe the PO was trying to compensate with different plugs. GS bikes are known for carb issues (as any 30 year old machine would be) so I would replace ignition parts with known good ones and if it persists your next step is the carb block.
Click to expand...
See first post, it's mainly electrical. I have cleaned out the RH carb about 4 times already:cry:
 
SqDancerLynn1 said:
First thing to do is make sure the battey is fully charged. Dead battery will cause it to miss.
Click to expand...
Sure, but it misses much more on one side than the other, even with a fully charged battery. There's clearly a problem on the RH side. This has the particular effect that if you want it to idle, it runs for a while, misses a couple and then dies. So, idling is impossible until I have a reliable spark on the RHS.
SqDancerLynn1 said:
New plug caps wouldn't be a bad idea, get NGK caps
$3-4 @
Click to expand...
Agreed
 
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