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Discussion Starter #1
About 6000 miles on the 2012 Voyager and I thought I may be running too lean, so I pulled the plugs to check it out. The plugs looked fine but I replaced them anyway since I already had it apart and purchased new ones (OEM spec NGK). I buttoned it all up and went for a ride. Ouch, horrific spark knock from the rear cylinder. I removed and inspected the rear plug and saw nothing wrong with it. So I double checked the gap, installed and torqued to spec. This time I ran it up before putting the tank back together and the knock was still there. So I pulled it out, then cleaned and gapped the old plug and put it back in. No knock, it runs great. I suppose the plug could be bad, I didn't have another one to try. But that seems unlikely with no sign of physical damage. Any ideas??
 

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About 6000 miles on the 2012 Voyager and I thought I may be running too lean, so I pulled the plugs to check it out. The plugs looked fine but I replaced them anyway since I already had it apart and purchased new ones (OEM spec NGK). I buttoned it all up and went for a ride. Ouch, horrific spark knock from the rear cylinder. I removed and inspected the rear plug and saw nothing wrong with it. So I double checked the gap, installed and torqued to spec. This time I ran it up before putting the tank back together and the knock was still there. So I pulled it out, then cleaned and gapped the old plug and put it back in. No knock, it runs great. I suppose the plug could be bad, I didn't have another one to try. But that seems unlikely with no sign of physical damage. Any ideas??
Bet it is the new plug.
Just because it is new & no noticeable damage, does not mean there isn't any.
Bought a pack of fuses once, could not see any damage, all looked ok, but the 1st 3 I used did not work
 

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i have had this before
i was a mobile mechanic and drove out to a jag not going that the customer had serviced him self and would not start .
checked all the normal thingsout and was fine ,the brand of plug i didnt like but they tested fine out of the car ,after 1hour of double checking i said i am going to put in new plugs from the brand i carried and it started first go ,so put half the pugs back and it missed ,they broke down under load from compression
 

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In 36 1/2 years workin on skoots I have sold and installed literally thousands of plugs. This ole memory of mine can't remember how many but I have experienced the occasional bad new plug, and it certainly sounds like you got one.

One thing I have to mention is due to the Iridium tipped design of these plugs I have seen no reason to change them untill at least 30,000 miles, maybe more. This is of course dependant on proper tuning (i.e. not running rich). I replaced mine at just under 22,000 mls cuz like you I was already there doing coolant change and other stuff, but the original plugs were in perfect shape with no electrode wear, the gap was still in factory specs!

RACNRAY
 

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Discussion Starter #5
Thanks for the feedback. I've been a shade-tree mechanic for about 40 years and have never run into a bad plug out of the box. Obviously defects are possible with any part, but with my limited experience I didn't know if it was likely. It seems to be running great right now so I guess I'll check it out again in another 25,000 miles. Thanks again.
 

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If it ain't broke... don't fix it...... I have had a couple bad plugs in the past and it will drive you crazy...... plus other new parts that were bad.... the first thing I thought was I had damaged the wire some how....

My plugs looked great at 8k miles.... I ran the plugs in my Venture over 50k before I changed them and they looked well enough to leave also. But like a lot of things, it is a pain in the rear to get there so go ahead and change them.... 240k miles only 4 sets of plugs.....
 

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Discussion Starter #7
Good advice, Bubba. I had done several things to the bike at the same time so I thought sure that I screwed something up. The biggest thing was removing all the vampire connectors on the PCV wires and replaced them with soldered pigtails and spade connectors. I only replaced the plugs because, well, it was already apart. Since I had never experienced a bad plug out of the box I thought sure I'd screwed up the wiring. Man, was I worried, but everything is good now. And eliminating the vampire connectors seems to have cured the problem I had with a surging cruise control in 6th gear. All is well that ends well.
 

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GLAD TO HEAR...when our skoots are happy boy o boy WE sure are happy!!
 
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