first ride yesterday - fail ... bad plug

[Max]

Revitalized bike from seat forward past 11 days, elbow grease, re-enforcing all cracked plastic tabs, stress points any other such defects with plastic epoxy.

Reduced progressive spring spacer from 3/4 to 1/4" and lowered fork fluid to 6.5" for softer ride. Added washers to tighten floppy CMS unit. Found and cleaned

a couple of corroded electrical connectors, greased speedo cable .. on & on. So, after a long winter and just shy of a couple of weeks of maintenance, finally prepped

and jacked for First Ride.

 

Great, 2 hour window, 50*f, bike starts spot on, idles ok but feels 'off' a bit. It ran rough at all rpm and never did clean itself out so decided to bail. Thinking with all the

wrenching over the winter I surely screwed something up.

Lucky, it didn't take long to find the problem. With hot engine idling, I'd get this subtle misfire about every 10 seconds. Checked the carb throats and found #3 puffing out vapour bubbles in sync

with misfire. Replaced plug and trouble cleared. Sort of a lesson learned, this is the first time in 41 years of riding I decided to re-use plugs consecutive seasons, bad luck eh? So much for

NGKIridiums. The business end of the plug was coated in dry black carbon but didn't look fouled. Needless to say, replaced with 4 new standard NGK's this aft (carb sync checked ok)

and had a chilly,but good 2 hour run around Kawartha Lakes, and it felt great.

[bongobobny]

Yup, they will eat plugs! Nice looking ride you have, lots of aftermarket chrome on it!

[BlueSky]

When I bought my 85 Kawasaki ZN700, it only had 1,053 miles on it. The oe had passed and his nephew tried to clean the carbs and get it running. It was running ragged on 3 cylinders when I bought it. Turned out to be a completely dead plug. I'm sure they were the original 24 year old plugs but they were low miles! Ha! A bottle of Valvoline complete Fuel system cleaner in a tank of gas and new plugs and it runs like a champ.

[jasonm.]

why was the plug bad? oil fouled or gas fouled. FYI..gas fouled is due to the ethanol around me damaging the floats causing the fuel level to rise. Also if valves are too tight it also shows up as a misfired due to low compression. FYI- I had both these issues. With that same symptom. Another odd one is a bad spark cap when they get hot. They will arc out to the head. Run it again and let it idle hot and see if it's truly resolved. I mean idle 5-10 minutes after a ride.

Edited April 20, 2015 by jasonm.

[Max]

why was the plug bad? oil fouled or gas fouled. FYI..gas fouled is due to the ethanol around me damaging the floats causing the fuel level to rise. Also if valves are too tight is also shows up as a misfired due to low compression. FYI- I had both these issues. With that same symptom. Another odd one is a bad spark cap when they get hot. They will arc out to the head. Run it again and let it idle hot and see if it's truly resolved.

 

Jason, I think the plug was just plain old defective. The ignition end was black but dry. After replacing the defective plug, the misfire & power lag cleared out. What I didn't mention was when I reinstalled the suspect defective plug to make absolutely sure it was the problem, the trouble returned instantaneously.

I had the 87' out shortly after replacing all plugs and it idled as it should and ran like a scared rabbit. Actually had her out today for about an hour and ran & idled fine.

 

Initially, my worse fear was something I`d screwed up during maintenance or one of those nasty troubles I`ve read about here, such as you`ve mentioned. I`m gaining an incredible amount of mechanical knowledge thru VRO members, and any repairs I can steal from the stealers makes me happy. I consider myself lucky it was a simple fix this time.

[jasonm.]

I no longer use NGK plugs. I had 6 out of 8 go bad in the worst way. They electrically OPENED internally in less than 2000 miles. Suppose to be 5k ohm resistance on each plug. Both resistor and non-resistor type did this=Infinite resistance. No, it's not my wires or caps as wires are new caps test good and caps were cleaned internally by me. All tested by me a 30+ years working on electronics. FYI- NGK caps go bad quickly too. Now using Denso iridium IX24B. No problems past 6k.

[flyday58]

I no longer use NGK plugs. I had 6 out of 8 go bad in the worst way. They electrically OPENED internally in less than 2000 miles. Suppose to be 5k ohm resistance on each plug. Both resistor and non-resistor type did this=Infinite resistance. No, it's not my wires or caps as wires are new caps test good and caps were cleaned internally by me. All tested by me a 30+ years working on electronics. FYI- NGK caps go bad quickly too. Now using Denso iridium IX24B. No problems past 6k.

Interesting. I'll look into these myself.

[Brenner]

[Ben Rollins]

I bought new plugs and see that the book says to gap at 31-35, What should I gap at? The old plugs I pulled out were showing 37.

[Ben Rollins]

I bought new plugs and see that the book says to gap at 31-35, What should I gap at? The old plugs I pulled out were showing 37.

[Max]

I bought new plugs and see that the book says to gap at 31-35, What should I gap at? The old plugs I pulled out were showing 37.

 

I shoot for .033 using a wire gauge with snug .034.

Lots of tech reading online concerning pros & cons of over and under gapping.

[jasonm.]

these are very well designed engines. Over-gapping causes more issues than under-gapping. Since all plugs slowly open over time I did mine at .032. Also being iridium the gap changes slower than standard plugs. I have old standard plugs and none had opened more than .003 after 15k miles. I still have them as spares because the center electrodes had zero wear after 10k. Another set with 15k also zero...used a magnifying glass and compared to new. I think NGK is secretly making plugs in China or cheap clones from China , or they truly changed the way they are made...= cheap. My NGK trust is out the window. I had the bad plugs on my desk for years to remind me NOT to buy them again. I think I finally threw them out. I tried Autolite plugs. The resistance varied to over 7k on some. And the Threads are poorly cut aka rough edges..basically not quality from a manufacturing standpoint . Threads are either cut or rolled...these looked rolled from rough pitted steel , bla bla bla...just don't like them.

Edited April 20, 2015 by jasonm.