To Resistor Cap Or Not To Resistor Cap? That Is The Question!

[Tom H]

Tried the search here as well as Google. Came away confused

I'm kinda looking for a yes or no type answer. I'm not an electrical engineer, so much more than that would be lost on me.

So, for my '04 EV. It has resistor plugs. Does it need the NGK plug cap as well? Does this bike suffer from the bad caps that I've read about on other models?

My Eldo and Ambo always have been plug and cap non-resistor. Any reason to go with resistor cap?

I read and understand enough that the resistor cuts down on interference, slows the spark down to make a longer duration spark.

Is it a bad thing to have both plug and cap resistor?

Thank you!!
Tom

[guzzisteve]

I use a resistor cap but not a plug. If you have strait caps then use a resistor plug. Only 1 in spark circuit if at all.
I talked to a Champion Rep and it straitens out the ark. W/O it loos like a lightening bolt and w/1 it is a strait ark, no jagged edges.

[ITSec]

My understanding is one or the other but not both.

[KiwiKev]

Resistor does nothing to enhance the spark - just weakens it, IMHO a jagged (lightning bolt) spark will ignite the fuel / air mix better than a clean one.

my bro Kiwi Roy will know the full story :-)

[Rough Edge racing]

 Your car or truck has resistor wires and resister plugs... about 15K ohms total per cylinder .....Does you bike need that much suppression? depends on the onboard electronics, if any.....

[Kiwi_Roy]

You only need one resistor, there are 3 types that I know of.
I remember when they started installing resistors to cut down on TV / radio interference.

1) Plug
2) Cap - this is my personal preference, don't ask me why
3) Lead (nasty carbon core HT leads)

Pull the cap off each side and measure from cap to chassis (cap and coil in series). it should be the same on both sides.
Last time I measured one it read about 8K Ohms


Hi Kev, how's the Guzzi coming on?

[StuCorpe]

On the 03 EV the resistor cap was a 5KΩ cap, they come in various resistor ranges with 1 KΩ, 2KΩ and 5 KΩ being the most common.

[Wayne Orwig]

My 04 EV has both resistor plugs and caps.

When I replace them, I put back resistor plugs and caps.

The extra resistance tends to make the spark duration slightly longer. Probably meaningless.
The extra resistance may tend to cool down the spark, slightly lowering the current. Probably meaningless.
The initial arc voltage will remain the same.
Since the current is lower, there will be less RFI. The ECU has a LOT of wires running around to temperature and timing sensors. RFI is a BAD thing. Using the second resistance is NOT really a bad thing. I favor the second resistance set to reduce RFI.

In the end, it is unlikely to matter.

[Rough Edge racing]

 Resistance does shorten the spark duration.... This may matter in a marginal situation..... The ignition in my 96 Ducati 900M has no problem firing a .030 gap plug at 7500 rpm with  5K ohm NGK plug caps with non resister plugs and wires....Guzzi ignition and requirements must be similar...
 

[bmc5733946]

I'll side with Wayne on this. Built that way, works that way, might not work as well without, no reason to change etc, etc, etc.

Brian

[Tom H]

ITSec, RER and guzzisteve, that was my thinking from what I was reading on the "net". Makes sense to use only one.

So....Armed with this info, I grabbed my trusty multimeter and set off to see what my EV has. With all the help I was able to figure out what I was looking for!

I first figured out how to set the meter for the correct ohm range. I have a NGK resistor cap in my parts stash and played with the meter ohm range setting until it read 5.2K or the like.

So I first measured the resistance by pulling the plug wire off the plug and putting one test lead into the plug cap and one to a frame ground and found 8.2K ohm about. The coils on this bike, I think, have 3K ohm resistance. So added up, 3K for the coil and 5K for the cap is 8K ohm, the STOCK plug cap has a resistor built in (verified by pulling the stock rubber style cap off the wire, measuring the resistance and reading on the cap 5000. Go figure it was molded into the cap ).

So just like Wayne stated, the EV has a 5K ohm resistor cap and as per the manual for the required plug NGK BP"R"6ES resistor spark plug. Interesting??

It appears that for some reason Guzzi decided to go with both resistor caps and plugs on AT LEAST this model (probably more??). I would have thought only one as mentioned by the replies. Maybe the ECU needs more RFI reduction??

This all got started by the threads on bad plug caps leaving you stranded and thinking that I should replace the plug caps. I just wanted to make sure I used the correct plug cap.

Thank you all for taking the time to help me learn something I didn't understand!!

Heck, I may try the NGK caps on my Eldo and see if it makes a difference.

Tom

[Wayne Orwig]

I just went out to my 2004 EV, in the rain, re-measured the original cap. It is 5K ohms (not 5 ohms).

And no, the bad plug caps are on many of the 8V models only.

[KiwiKev]

You only need one resistor, there are 3 types that I know of.
I remember when they started installing resistors to cut down on TV / radio interference.

1) Plug
2) Cap - this is my personal preference, don't ask me why
3) Lead (nasty carbon core HT leads)

Pull the cap off each side and measure from cap to chassis (cap and coil in series). it should be the same on both sides.
Last time I measured one it read about 8K Ohms


Hi Kev, how's the Guzzi coming on?

Lol, good question Roy, I bought a 27mm deep socket yesterday for the back bearing nut if I can call that progress. Off to Melb next Monday, the old boy coming too so may rope him in again.

Could take the box with me and work on it there, or call in on Pete Roper - lol.



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[Kiwi_Roy]

I just went out to my 2004 EV, in the rain, re-measured the original cap. It is 5K ohms (not 5 ohms).

And no, the bad plug caps are on many of the 8V models only.

My 98 EV had resistor caps and the resistor leads, it started miss-firing on one cylinder and I found the lead on one side had opened up
It measured ~ 8K on one side and infinity on the other from cap to chassis.

I never thought to measure the plugs

[Tom H]

My bad on the ohm numbers. The 5.X should have read "I think" 5.X "K" ohm. and the 5000K and the ohm symbol on the plug cap "I think" should be just 5000 ohms.

Like I said, not good on the ohm stuff. Just one of those things in life that I could never get straight. I'll edit the post to add the K.

Wayne, you didn't need to get drenched to check  And thanks for clearing up the bad cap model, thought it might have been all electronic ignition bikes.

Thank you all very much again!
Tom

[pete roper]

I just went out to my 2004 EV, in the rain, re-measured the original cap. It is 5K ohms (not 5 ohms).

And no, the bad plug caps are on many of the 8V models only.

And certain single TB V7's too.

[wirespokes]

It's my understanding that points ignitions need 1K ohm per side and Electronic take 5K ohms. From what I gather, without the resistance, the coils or electronics can be damaged so has more to do with that than spark profile. No idea why both resistor caps and resistor plugs are used together.

[Rough Edge racing]

It's my understanding that points ignitions need 1K ohm per side and Electronic take 5K ohms. From what I gather, without the resistance, the coils or electronics can be damaged so has more to do with that than spark profile. No idea why both resistor caps and resistor plugs are used together.

 Points ignition needs no resistance in the wires or plugs for proper operation.It was common yeas ago to use solid core wires and non resister plugs in car/trucks and some bikes...A simple electronic ignition might not need any resistance for RFI reduction...The popular Pazon Surefire electronic ignition for vintage Brit and European bikes is an example...
  But too much spark interference on some electronic ignitions and or electronic fuel injections can cause all sorts of glitches...

[sib]

Whatever the technical requirements are, the 1TB V7s all come equipped with resistor plugs as well as resistor plug caps, 5K each.

[Wayne Orwig]

It's my understanding that points ignitions need 1K ohm per side and Electronic take 5K ohms. From what I gather, without the resistance, the coils or electronics can be damaged so has more to do with that than spark profile. No idea why both resistor caps and resistor plugs are used together.

Both work well with or without resistors. The coils will not be damaged without resistors on the secondary side to the spark plug. The spark plug tip may erode a bit faster.
Mainly, resistors are used to reduce RFI. Radio interference. Pretty meaningless with points. But the RFI can interfere with electronic sensors. So it tends to be more important to have resistors, if you have electronic ignition. It is highly unlikely to damage anything, it just may screw things up. Make a computer think a cold engine is hot, or the throttle was momentarily closed, that sort of thing. And even that is unlikely, but real. Many people encounter a screwed up Stelvio dash when the spark plug car was arcing around the resistors.

[Tom H]

Just a thought. Maybe Guzzi used both plug and cap in case one of them failed?

Thank you all again for the info!!
Tom

[sib]

Just a thought. Maybe Guzzi used both plug and cap in case one of them failed?
...

Resistors usually fail by opening rather than shorting.  These resistors are in series.  If either one fails it will open the circuit.