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Old 03-02-2015, 05:38 AM   #1
Spaggy OP
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Spark plugs failing

I have a 78 Kawasaki KZ650B and it has been killing spark plugs. I found 2 bad plugs (no spark) so replaced all 4. NGK BR7ES. Couldn't find the ones without resistors. Bike ran great before and has been sitting on a battery tender waiting for it's inspection to be put on the road this summer. Now I have 3 more plugs failed and the only running the bike has done is to move it from one side of my shop to the other. I replaced all 4 again and runs great now.
When i check the plugs with an OHM meter, they are leaking from the electrode to ground.
My question is what the hell is killing my plugs? Did I just get a bad batch? Should I try to find a set without the resistor?
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Old 03-02-2015, 11:08 AM   #2
Pigford
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If the bike is running points - don't use resistor plugs!

Modern NGK are crap... theres loads of cheap copies made in China nowadays.

Try a new set of Denso plugs.
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Old 03-02-2015, 11:57 AM   #3
MODNROD
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My old 1981 Z750E went fine until I added a bit of comp and flat slides, then it started to eat plugs just like yours does (yes, it was tuned OK). I used to get about 1000km out of them, then they were toast from misfiring. This was about 15 years ago, but back then NGK were longer lasting than Bosch or Champion, all 3 weren't good.

I went Denso and doubled the plug life.
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Old 03-02-2015, 12:15 PM   #4
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The Denso IRIDIUM are v. good - bit pricey tho' ran the same set in my Z1000 - 1075 Wiseco hi-comp motor for 4 yrs with no probs...



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Old 03-03-2015, 04:31 AM   #5
Spaggy OP
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Thanks guys. It is running points. I found a set of autolites that change up with no resistors. I'll get the inspection done and worry about fine tuning later.
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Old 03-03-2015, 05:09 AM   #6
przjohn
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You can but NGK non resistor plugs on Ebay all the time.
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Old 03-04-2015, 07:33 AM   #7
Andyvh1959
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On older Jap bikes I always replace the plug caps, and trim the coil wires back about a 1/4" when I install the new NGK plug caps. Each cap is less than $7 and well worth the results. Old plug caps increase in resistance over time and can lower the voltage to the plugs.

Same for a corroded plug wire. Pull off the old plug caps and check the end of the coil wire, very likely it is dark or corroded green. Same for all the connections in the circuit from the fuse panel to the Kill switch, ignition switch and wiring between the points and input 12 volt to the coil primary. Check and clean them all to get the most juice to the plugs. Change out the points and condensor if you haven't done so already. Make sure the inside area of the points cover is clean and dry, moisture under the points cover can defeat the trigger signal to the coil.

Moisture can also affect the coil leads to the spark plugs. The old trick used to be wipe the coil wires with a wet cloth and then fire the bike up in the dark (lights off) and watch for any sparks jumping from the spark plug leads to the head. Old cracked plug leads leak voltage to whatever ground source they can find, and the resultant weak spark quickly fouls the plugs. Years ago I corrected a lot of issues on my brother's 80 Yammy 650 Seca and it always started and ran great.
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Old 03-04-2015, 10:24 AM   #8
baldman1
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Starting the bike and not riding it will kill plugs also, it doesn't give them enough time to get hot and burn off the carbon. So if you keep starting it and not allowing it to warm up then eventually you will foul the plugs up.
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Old 03-06-2015, 03:57 AM   #9
Spaggy OP
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Quote:
Originally Posted by Andyvh1959 View Post
On older Jap bikes I always replace the plug caps, and trim the coil wires back about a 1/4" when I install the new NGK plug caps. Each cap is less than $7 and well worth the results. Old plug caps increase in resistance over time and can lower the voltage to the plugs.

Same for a corroded plug wire. Pull off the old plug caps and check the end of the coil wire, very likely it is dark or corroded green. Same for all the connections in the circuit from the fuse panel to the Kill switch, ignition switch and wiring between the points and input 12 volt to the coil primary. Check and clean them all to get the most juice to the plugs. Change out the points and condensor if you haven't done so already. Make sure the inside area of the points cover is clean and dry, moisture under the points cover can defeat the trigger signal to the coil.

Moisture can also affect the coil leads to the spark plugs. The old trick used to be wipe the coil wires with a wet cloth and then fire the bike up in the dark (lights off) and watch for any sparks jumping from the spark plug leads to the head. Old cracked plug leads leak voltage to whatever ground source they can find, and the resultant weak spark quickly fouls the plugs. Years ago I corrected a lot of issues on my brother's 80 Yammy 650 Seca and it always started and ran great.
Thanks for the great tips. 12v wiring is all clean and it had new points and condensor. I will check the plug wires like you said though.
I did ride it about 10 km after getting the inspection done and it's running really good with the non resistor plugs. What a fun little bike.
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Old 03-06-2015, 10:25 AM   #10
baldman1
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What is the coil voltage at the primary wire for the coils? It should be 12 volts, if it's lower than 10 volts then you are not getting the proper voltage to the coils, it will run but foul plugs a lot.
Also are you using a lot of choke when starting cold? I have a customer who during the winter months will go out to his garage and start his bikes and leaves the choke on until they warm about 10 minutes. Well over time the plugs end up fouling out and then the bike will not start and he calls me. I keep telling him to not do that but to turn the choke off when the bike starts and modulate the throttle to keep it running until it warms up. He will not listen to me and I keep charging him to replace his spark plugs twice a year.

I have been riding the KZ650 since it's introduction in 1977. They are a fun machine, I bought this one in 1978 and have put well over 150,000 miles on it, I still own it. It's been from California to New York, Canada and Mexico, Very reliable, fast, fun and gets over 40 mpg. Have fun with it.
The only issue I really do not like with the engine design is you have to remove the camshafts to change the valve clearances. It's a good thing the valve clearances really don't change much.

baldman1 screwed with this post 03-06-2015 at 10:31 AM
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Old 03-06-2015, 02:22 PM   #11
England-Kev
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just buy Denso's
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Old 03-06-2015, 03:26 PM   #12
travlr_45
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This is an interesting thread for me, I have a 1970 CL 450 here that's been doing the same thing lately. I've been considering the idea of a CDI ignition for it but would prefer to keep it as original as I can.
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Old 03-07-2015, 04:39 AM   #13
Spaggy OP
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I'll have a look at coil voltage too. I hear that a common mod is to run switched power straight to the coils, bypassing kill switch etc.
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Old 03-07-2015, 11:46 AM   #14
k-moe
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Quote:
Originally Posted by Spaggy View Post
I'll have a look at coil voltage too. I hear that a common mod is to run switched power straight to the coils, bypassing kill switch etc.
Just because it's a common mod does not mean that it's a good idea. If there is voltage loss through the feed to the coils the thing to do is deoxidize all of the switches and connections in that circuit.
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