Spark Plug question

[dmoff1698]

Something I've always wondered about.

 

First a little about my riding habits.

I have a 99 RSV that I have owned since 2000. I ride on average 13-15K miles per year. Around 90% hiway miles and about 50% 2up. I don't race my bike, but I don't baby her either, I don't mind bumping the rev limiter once in a while, but don't do it every day.

 

Now for my question.

 

Why is it that my spark plugs only last around 10K miles at the most? The bike will run fine at lower to midrange RPMs, but at higher RPMs it feels like a miss or fuel starvation. Change plugs and all is good again.

 

I run the recomended NGK DPRE8-9. I've tried equivalent Bosch but there's no difference.

 

When I change the plugs, they are a nice grey/tan color with no signs of eroding, still gaped to spec (hurts my soul to throw them away). Look as good as new.

 

Why can I get 90-100K on my plugs in the car, and less than 10K on the bike?

[V7Goose]

Sounds to me like you have a weak spark - probably plug caps or wires, maybe both.

 

Easy to check the resistance of the caps - been discussed here in many older threads. Should be about 10K each.

 

Plug wires are not replaceable (officially), but fairly easy to check with a spray bottle after dark. The darker the better for this test. Start the bike, adjust the spray to the finest mist possible, and start misting around each wire. Be sure to briefly snap open the throttle several times while watching each wire, since that is the point when the spark has the toughest time. If the wires are bad, you will see sparking or a blue aura around the wires during this test.

Goose

[Black Owl]

Sounds to me like you have a weak spark - probably plug caps or wires, maybe both.

 

Easy to check the resistance of the caps - been discussed here in many older threads. Should be about 10K each.

 

Plug wires are not replaceable (officially), but fairly easy to check with a spray bottle after dark. The darker the better for this test. Start the bike, adjust the spray to the finest mist possible, and start misting around each wire. Be sure to briefly snap open the throttle several times while watching each wire, since that is the point when the spark has the toughest time. If the wires are bad, you will see sparking or a blue aura around the wires during this test.

Goose

 

Good response Goose. Now, if he does have Corona (No, not the beer), how does he correct the problem if the wires are not "replaceable".

[V7Goose]

Good response Goose. Now, if he does have Corona (No, not the beer), how does he correct the problem if the wires are not "replaceable".

Gee, I was gonna wait until he said he actually had the problem so I could ride in on my silver horse and save the day! Oh well . . .

 

Officially, the only option is to replace the coils with attached wires.

 

The cheaper solution is to find a source for NGK wire splices (or any other brand), buy some new stranded copper plug wires in any color that excites you, cut the old wires off about 1.5" from the coils and screw the new wires on. All done.

Goose

[Black Owl]

Boy, nothing like making it easy for the shade tree guys....

[dmoff1698]

Are you telling me that you are getting a lot more miles out of a set of plugs than I am?

 

It's been this way pretty much since I've owned the bike, thought it was normal.

 

If 10K on a set of plugs is not normal, then I gots some looking to do.

[V7Goose]

Your plug mileage is absolutely not normal. Although the specified change interval is 8,000 miles, many of us go 20,000 to 50,000 on a set without problems. Your descriptions said the plugs look good when you pull them, so I doubt there is anything actually wrong with them, just that your bike is barely able to make the correct spark even when they are new. That problem is probably not on all cylinders.

 

10 years is plenty long for plug wires to break down, but that is more common with carbon core than our copper core wires. Your most likely problem is the plug caps. A weak battery can also contribute to the problem.

Goose

[dmoff1698]

Sounds to me like you have a weak spark - probably plug caps or wires, maybe both.

 

Easy to check the resistance of the caps - been discussed here in many older threads. Should be about 10K each.

 

Plug wires are not replaceable (officially), but fairly easy to check with a spray bottle after dark. The darker the better for this test. Start the bike, adjust the spray to the finest mist possible, and start misting around each wire. Be sure to briefly snap open the throttle several times while watching each wire, since that is the point when the spark has the toughest time. If the wires are bad, you will see sparking or a blue aura around the wires during this test.

Goose

 

Just got the chance to look at my spark plug caps this morning. Here is what I found.

 

First thing, I disconnected each SP wire from the plugs, and measured the resistance through the cap, wire, and coil to ground. All 4 measured around 28.2K to 28.6K ohms. I was supprised they were so close to each other.

 

Unscrewed the caps from the wires and disassembled. Did not think to measure the caps seperately. You were right about corosion inside, though it only appeared on the end of the spring toward the wire. See the pics below.

 

Cleaned up the caps and components and reassembled. Measured the cap resistance on each and had a low of 9.6K and high of 10.2K.

 

Before reassembly, I measured the resistance of the wire and coil to ground and all read around 12.2K to 12.6K. I was supprised, expected it to be lower.

 

Reinstalled the caps on the wires and took another measurement through the caps to ground, they range from 22.2K to 23K.

 

I lowered the overall resistance all around, but did not get to the 10K you discussed. Watt chew tink?

[V7Goose]

Just got the chance to look at my spark plug caps this morning. Here is what I found.

 

First thing, I disconnected each SP wire from the plugs, and measured the resistance through the cap, wire, and coil to ground. All 4 measured around 28.2K to 28.6K ohms. I was supprised they were so close to each other.

 

Unscrewed the caps from the wires and disassembled. Did not think to measure the caps seperately. You were right about corosion inside, though it only appeared on the end of the spring toward the wire. See the pics below.

 

Cleaned up the caps and components and reassembled. Measured the cap resistance on each and had a low of 9.6K and high of 10.2K.

 

Before reassembly, I measured the resistance of the wire and coil to ground and all read around 12.2K to 12.6K. I was supprised, expected it to be lower.

 

Reinstalled the caps on the wires and took another measurement through the caps to ground, they range from 22.2K to 23K.

 

I lowered the overall resistance all around, but did not get to the 10K you discussed. Watt chew tink?

You did find exactly what I suspected, you just did not understand. I specifically said the cap resistance should be about 10K each, which is what you got after you cleaned them.

 

You cannot measure the secondary coil winding to ground - these coils have a very odd construction where one end of the secondary coil is tied to the same +12V terminal that the primary coil winding uses (+12V from the ignition fuse and kill switch on the R/B wire).

 

If you did not check the wires for leakage in the dark like I described, you still need to do that. Only now that you have fixed the caps the wires will function better anyway. I suggest that you pop off one of the plugs wires from a rear cylinder when you do the test - that will give you the best chance of seeing any arcing from that wire - if it is good, all of them will probably be good.

Goose

[dmoff1698]

OK thanks,

 

Now I just have to find a dark place to work. My shop has sky lights and a yard light right outside. Just have to see if it's dark enough to tell if I'm getting arcing or not.

[gibvel]

OK thanks,

 

Now I just have to find a dark place to work. My shop has sky lights and a yard light right outside. Just have to see if it's dark enough to tell if I'm getting arcing or not.

 

You're lucky. All the brass spacers in mine fell apart into about 3 or so pieces each. I made more but, believe you me, that wasn't the most fun thing I've ever done.

[KiteSquid]

OK thanks,

 

Now I just have to find a dark place to work. My shop has sky lights and a yard light right outside. Just have to see if it's dark enough to tell if I'm getting arcing or not.

 

Wait for a moonless night, turn off the yard light and it should be dark enough.

 

 

OR you might mask off the skylight for the test.

[V7Goose]

FYI - this thread is a year old; not much point in replying to it.

[Zane]

FYI - this thread is a year old; not much point in replying to it.

 

Thanks Goose, I missed the date! Will delete!