Bad spark plugs???

[jasonm.]

Okay, I bought new plugs for my 87VR. So I could check how the bike is running, clean or not? Well after 500 miles on the new plugs I got some misfires at idle when hot. Like when doing a carb sync. or setting the low speed screws w/digital tach. 1st let me say I did all these same things 2 month ago w/old plugs and had no misfires. Now I decided to check everything before getting ready for Americade next week. I have new spark plug wires and caps as of 4 years ago . The misfired showed up as a loud tick coming right from the spark plug cap of #3 & #4 along with a skip or drop in rpm while simply idling, which shows clearly on my digital tach. I changed the spark cap...no change in problem. Then changed the spark plug and problem gone. The plugs removed are clean, not fouled. My low speed screws for all cylinders when adjusted show an obvious "sweet spot" varying from 2.25 to 3.5 ccw. Not trusting these new NGK DPR8EA-9 plugs. I now have all my old NGK plugs back in. I may try to get non-resistor DP8EA-9. Fact being, it's normally the resistor element being faulty under extreme heat that causes the issue. I do not like iridium plugs as the electrodes are very sensitive and should not be touched by even a gap gauge. I guess even Japan is making crap these days...Anyone else had similar problems like this???

Edited May 26, 2009 by jasonm.

[CrazyHorse]

I use the Iridiums with no problem.

[Venturous Randy]

I have used the el cheapo Autolites from Advance Auto for years and they seem to do real good.

Yes Jason, I would suspect you had a bad plug.

RandyA

[jasonm.]

The Advance Auto that I bought the NGKs($2ea) from offered me the Autolites($3 pair) or a swap for the bad one(s). They claimed the Autolites were non-resister. Which sounded like what I wanted. Hoping to avoid a repeat of the above in the future. Got them home and checked them. They had 4.5k ohm each. Same as the NGK. Thus not what I really wanted after this pain. You don't need resistor plugs with the stock(10k) caps. On another thread I expressed my hate for NGK caps. As I have had them fail. Showing the same symptoms as the bad plug problem. But the failure I had was w/non-resistor plugs. Which always makes it easier to find the cause of a misfire. TO confirm it was the spark plug(s). I replaced the plug with an old one and let the bike idle for 15+ minutes. Keeping the temp. at 3 o'clock on the dash using a fan. No skip or misfire. Idled @ a solid 1000. I remember someone else saying they had a bad plug before. Wonder if he had the same symptoms? Just wish I could remember who it was? Now I am getting shakey about taking the Venture to Americade...what next. What did I miss? Still think the carbs have to come out....see my other thread of carb concerns...

[Gearhead]

Weird, I've never had a bad brand-new plug, but if the problem went away when you put the old one back in, sounds like you've found it. Can you ride the bike to work a couple times for a shakedown? If that's all good I'd take her on the ride.

 

I've also never had a problem with resistor plugs. The spark pulse doesn't really travel THRU the wire per se, but rather on the surface of the wire. Something weird about high voltage. As such, the many k ohms of resistance don't really affect the strength of the spark much either. I think that non-resistor will be more likely to cause noise on your radio system. The caps take the place of resistor wires (since the wires are simple copper stranded wire). Cars always have resistor wires and plugs for RFI supression.

 

Well, that's my 2 cents, anyway.

 

Jeremy

[GeorgeS]

Get a set of Iridiums, !!! Are you going rideing, or are you going to play polker with

Spark Plugs ???

 

Put in 4 NEW plugs, and quite messing around--- Its Spring, the Sun is shinning !! Its time to Ride ----

 

And don't forget, your not paying Sales Tax!! on a new Harley !!!!!

 

And I was the guy, who got Bad New plugs on a few occasions over the years.

Once for a Chevy V8, and one set of new stock NGK's for my bike. ( one of them was bad. )

[jasonm.]

I have either a rich issue from the carb rebuild. Or had a bad plug. I changed the plug...problem gone. The non-resistor will be a bit less prone to fouling. I have used non-resistors in other bikes with no noise in CB or Stereo. I work in electronics. I do know that having 2 resistors in line, spark plug and cap DOES reduce efficiency.While one resistor(cap only) does not. Some guys use 5k NGK caps with the stock resistor plugs(also 5k)= 10k of the cap alone. I'll let you know how the non-resistors work. I did read the plugs. No obvious rich issue(soot) I could see after 400+ miles on them. Oh...and I will be carrying spare plugs on my trip.