Plug Caps & Coil Wires FAQ

compiled & edited by Kristian #562
 Please read the Disclaimer before attempting any work in this FAQ.
 

by Hombre sin Nombre & Kristian #562

 Adrian Jowett's Excellent F650 site was the first site to mention that the Plug Caps/Coil Wires/Coils can fail.

 

So what does he mean by fail.? Well they generally don’t suddenly stop working, they just build up resistance to the point where you spark gets weak and things don’t work like they used to.

 

The symptoms of Plug Caps/Coil Wires/Coil failure are poor starting, some mid range lag and possibly Poor Gas Mileage. Adrian noted that this didn't distinguish between the three, but you CAN test each of them and isolate which one it is.

 

Note that Starting and Running Problems can also be a rectifier going bad, which is covered in the Voltage Rectifier FAQ. If your bike has problems not wanting to rev over 1500 rpm when cold, try that FAQ first.

 

According to the Manual, secondary coil (plug lead to ground) resistance is 6-13k ohms. If you have one at 3k ohms, it may be the plug cap (Check this FIRST) OR the coil is going bad and should be replaced. They DO go bad - moisture can get in thru a microscopic crack, etc. Eventually, if the resistance drops too low (short), it may drain power from the good coil - if you are not having ignition problems yet, you may soon, as the 3k coil is probably not firing. Not sure if a dead short will damage the $300 CDI box, but you don't want to find out. If I were traveling across Africa with no spares, I'd disconnect the bad coil input (12v) wire (NOT the plug lead!) to make it back. I would not run with just one coil unless forced to. You might want to see if you get any spark from that coil. More below...

Note: Primary coil resistance (12v terminal - (Orange Wire) to ground) is supposed to be .2-.5 ohms.

 

Plug Caps:

 

 

For more Technical Details about the Plug Caps, see the section below.

 

Which Spark Plug Lead goes where?

 

Q. While I had the bike in bits I did some other maintenance and now have a really silly question. Which spark plug wire goes to which plug on the Classic? And what happens if you get it wrong? I


A1. Any!. And what happens if you get it wrong? Nothing ! If you get them on the correct plug they "sit" better that's all. Why not. They both fire at the same time!. It's  single cylinder, silly. Mal

A2. Mal is correct, but actually the short one is closest to the RHS. Think Right-Right, Left-Left. These were my replacement NGK leads. NGK Plug Leads.

 

Replacing the Spark Plug Caps:

 

 

 

  1. First pull back the rubber boot covering the connection between the Cap and the Wire. It can take a bit of coaxing and pulling. Both ends of my OEM coil wire were glued in with some sort of (dried) black adhesive sealer, similar to Yamabond/ThreeBond 1209, making an almost permanent connection.  It was very difficult to get the wire to break loose. While dielectric grease is OK when replacing the Rubber, in the case of such a critical wire that might break loose when handling the spark plug caps, I prefer the permanency of the Yamabond/ThreeBond 1209 glue/sealant. It's also there to keep water out.
  2. Now, grip the wire right next to the plug, either by hand if you have a strong grip, or with a pair of pliers (NOT ViseGrips and don't hold too tightly), and unscrew the Plug Cap from the wire. It easier to do this than undoing the wire from the Plug Cap.
  3. Remove the old Rubber Boot.
  4. Using a Good sharp or New Pair of wire cutters, cut about 1/4 to 1/2 (6-12mm) from the end of the wire you just wound out. This will both expose fresh wire and make for tight fit when you screw in the new Cap. Using an old pair of cutters will simply mash the end of the Coil Wire.
  5. Install the NEW Rubber Boot over the wire, making sure the wide open end faces the Plug Cap End of the wire. Pull the boot back so about 1-1 1/2 of Coil Wire are exposed.
  6. Inserting the point of the New Cap Screw in the centre of the newly cut wire, and holding the Coil Wire firmly (it should NOT be allowed to twist excessively), screw on the new Cap until you feel the Wire Butt up to the end of the Blind Hole in the Cap. (The Wire will start to turn with the Cap, at which point you should stop immediately - Do NOT try to overtighten.)
  7. Finally pull the rubber boot down the wire toward the Cap, until you can pull the boot over the new Cap. Repeat for the other Cap. That's it. You MIGHT like to test it before you start. See below for the testing procedure.

 

Repairing the Old Plug Caps: Rebuild#1 Replacing the Resistor
 

 

 

  1. Our OEM $38 BERU plug cap can be taken apart (unscrewed from inside) without removing it from the bike. The probable failure is an easily removable ceramic cartridge resistor, similar to an automobile fuse. If we could find a source of the OEM resistors, cap repair could be a 5 minute, $2 job, keeping the OEM cap, as opposed to using a $5 NGK cap (which will probably last forever). If anybody has a source for Beru parts, please let us know. However what you CAN do is buy or scavenge any 1kohm (BEST SOLUTION) or possibly at a pinch a 5kohm NGK Cap and Swap over the resistor.
  2. If you are scavenging 1kohm Resistors from NGK Straight Caps (for around $5US), look in the top of the cap. At the wire end, where the oil wire inserts, the wire screw is just an upside down self tapping screw, held in place with a couple of star washers (external lock washers), jammed down into the cavity against the resistor or a tiny spring. Instead of trying to grip the screw and yank it out directly, work the screw side to side with a small screwdriver to break the washers free, and the screw should come right out. Inside is the resistor and a small spring. The NGK caps are just fine, just the Beru's have the metal shields, are a bit tighter, and (until they rust) are sexier. :-).
  3. Unlike the straight NGK caps which come apart from the top, the NGK Elbow Caps come apart the same as the Beru, through the bottom, using a fairly large screwdriver to engage the notches in the brass insert, and unscrewing the brass insert to release the resistor and a spring. (Correct order shown) The plug cap does not need to be removed from the wire to remove/replace the resistor.
  4. By carefully mixing the springs and spacers from both caps (or substituting a longer spring), the shorter NGK resistor can be nicely installed in the Beru cap.  I'd suggest checking resistance/continuity with an ohmmeter to make sure it's assembled correctly and all the parts are touching.  Be careful not to install two springs against each other.  With vibration, they will eventually slip inside each other and probably lose electrical contact with the resistor, which would be a BAD THING. You can use two springs, as long as there is something solid in between them, like the resistor, or the metal spacer.  I figure a new NGK 5k ohm resistor was better than a Beru 1k ohm resistor failing to 50k ohms, at least until I find something better. The good news is that the shielded OEM Beru cap can be rebuilt without even taking it off the bike, or even taking the tank off, in about 10 minutes, for about $4.

 

Note that if the problem lies in one of your Coil Wires, or the Coil itself, then of course just replacing the Plug Cap won't fix your problem.

 

UPDATE - Sources of the Resistors:

 

1. Canadian Tire here in Canada has 1kohm Resistor Caps, they are the NGK LB01EP (says 1Kohm on the Side) - Cut them open with a hacksaw. The reason I so brutally hack-sawed them is because they are a 90 degree cap and the resistor is behind the 'wood screw' end, not at the spark plug end where you can just undo the brass cap. There is no way to get to the resistor without destroying the cap. Thanks to RacerRoo. Note the FAQ describes how you can work the "wood screw" out quite easily. Just pops right out if you work it a few times with a screwdriver.
 

2. http://www.800-airstar.com/ign.htm also shows 1kohm Caps are available. Thanks to Mason #631

 

If you actually want to test your existing caps you will need a resistance tester, commonly called an Ohmmeter, or VOM (Voltage/Ohmmeter), sometimes a DVM (Digital Voltmeter).  Almost any common cheap VOM will work for this, as long as it has a suitable (resistance) Ohms scale.  You can spend $20-$50 dollars for something perfectly suitable for general use, or $100's of dollars for something fancy. See Testing - Oooh Electrical Stuff, I don't know anything about that.

Beru Spark Plug Cap Rebuild: #2 Bypassing the Resistor
by Pete in Oz

Introduction:

As promised, here are the detailed instructions for a rebuild of the Beru caps. It's a little late because after a week and a half the bike wasn't running quite as well. After metering one of the plug-caps to ground I had one open circuit. When I pulled everything apart, I found I had two problems, first the Beru cap was open circuit internally somewhere in the top end (I gave up on it and threw it out at that point), second, I'd nicked (small cut) the HT lead which had broken near the coil end. Rebuilding with an NGK cap and the bike runs well again.

This should only be of interest to owners of older bikes, plug cap problems seem reasonably common after a few years and make the bike run badly rather than not at all. The performance difference is pretty dramatic, but that's mainly just from fixing the HT problems rather than some magic associated with how I did it.

Tools:

Parts:

Procedure:

Rebuilding the Beru cap:

  1. Spray some WD-40 down the Beru cap, leave it alone for an hour.

  2. Unscrew the inside of the cap, you DO need the right size flat bladed screwdriver. The thing you are unscrewing is brass and quite soft.

  3. Once you've unwound it as much as you can, tap the cap on a hard surface to get the internal brass threaded do-hicky out.

  4. If you are lucky, you'll also have the high voltage resistor, a stainless steel spring and a lump of something fall out as well. If they don't, keep on tapping. There are 4 bits in there. Mine were very corroded. The Blob is a Spacer.

    This picture is from an NGK Cap, but this is about what it all should look like:



    blob spring resistor threaded cap (Screw)

    You need all the bits.

  5. Lay the blob and resistor end to end. That's the length of brass rod you need.  The measurements are: 5-7mm diameter stock, either steel, brass, aluminium or some other conductive material. (quarter inch for you American Luddites), 37-40mm in length (inch and a half). Pop it in and it'll work. (from Shank).

  6. Cut it to the right length. (I'd suggest having enough of whatever to make several attempts if necessary).

  7. Next, get something, a long nail or a long small bladed screwdriver and try to scrape all the corroded crap out of the bottom of the plug cap. Give it a spray of WD-40 then mop it out with a Q-tip.

  8. Make sure one end of your rod fits inside the threaded cap. You may need to file it down a little and also clean up the ends if your hack-sawing was as ugly as mine.

  9. Clean up the spring, drop it back into the cap, drop the brass rod in, then put the cap back in. Tighten down. If you got it right, you'll feel the rod move a little against the spring if you push something down through the centre of the threaded cap.

  10. Next, clean up the screw at the other end of the cap (where it goes into the lead). You can try metering it now (good luck), it SHOULD read 0 ohms, if it doesn't, the cap is probably totalled.

Preparing the leads:

  1. The leads are 12 long, DON'T cut them to length yet. If you can, get an inductive lead long enough for several bike leads.

  2. Take the tank off the bike, remove one of the coils. (You cannot do this in place). Unplug the cap, unscrew either the plug or coil end of the ignition lead and remove everything.

  3. Stretch the old lead out, and make sure I was right on the length.

  4. Start at one end of the new lead. If it has a cap on it from when you purchased it, cut it off now. Move the coil end boot from the old lead to the new one. (Assembly is one shot only). See if you got lucky, does the lead screw right into the coil ?. If so, great, tighten it up, slip the boot on.

    If not: get the hobby knife and roll it around the lead about half an inch from the end. You want to just cut through the outer sheath, nick the inner and it'll break off when you try to screw it into the coil. That's why you still have one long length of cable, you may need a couple of attempts at this.!
     

  5. Trim off the braid with scissors, screw the cable into the coil, before you get to the end run silicone into the gap. It's HARD to screw in.

  6. Push the rubber boot over.

  7. Now, replace the coil on the frame, run the cable through the wire guide.

  8. Also: Make SURE you put the electrical connector to the coil back on at this point. It's easy to forget.

  9. Next, cut the lead to about 13, slip the cap end boot over, screw into the plug cap. You may need to do the trim thing here again, you may not. The extra inch doesn't make any real difference to fit, but gives you two shots at trimming it if you nick the core.

  10. Slip the boot back over the Beru plug, plug onto the spark plug.

  11. There should be enough fuel in the carbs for the bike to start. It's worth checking at this point.

  12. If you are doing both leads, repeat the above. As before, make sure the bike still runs.

  13. Replace tank/fairing fuel lead, tank vent hose.

  14. Go for a ride- preferably starting in a direction that's uphill from your house :-). Go round the block a few times. Get enough courage to go for a decent ride in the hills.

Look down at the rev counter while pulling out of a tight uphill corner and note that you are pulling away smoothly from 2500RPM when you used to have to be a gear lower and above 3500rpm or you'd stutter.

 

Feedback:

 

Testing - Ouch Electrical Stuff, I don't know anything about that:

 

The old-fashioned way

 

 

The new-fangled way

 

Feedback Q's

Q. Electricity baffles me. I read the FAQs & I'm still confused. I measured the Ohms between the cap and the coil. Gangers have said it should be between 6 and 13 ohms with the stock caps. So, I assume that if it is lower than 6 then it is OK? One cap is 4.5 and the other is 5.5 ohms.

Q. I took my one plug cap apart that was reading too low a resistance. When measuring the resistance of the ceramic cartridge resistor, I got a reading of "0", as in zero. Is that bad? I couldn't tell from the FAQs, but assume it is bad. On Monday I am going to an electronics store that may have the resistor we need. Do I ask for a 1k ohm resistor? If I put it on my meter while in the store is it supposed to read about 1k ohm?

Coil Wires

 

 

1.       Remove the Gas Tank.

2.       The Coil will be exposed. Pull the red wire off the Spade Connector at the back of the Coil.

3.       Remove the Two Bolts at the Coil and free the unit and wires from the Bike.

4.       Peel back the Rubber Cap at the Coil. Both ends of my OEM coil wire were glued in with some sort of (dried) black adhesive sealer, similar to Yamabond/ThreeBond 1209, making an almost permanent connection.  It was very difficult to get the wire to break loose. While dielectric grease is OK when replacing the Rubber, in the case of such a critical wire that might break loose when handling the spark plug caps, I prefer the permanency of the Yamabond/ThreeBond 1209 glue/sealant. It's also there to keep water out.

5.       Now, grip the wire right next to the Coil, either by hand if you have a strong grip, or with a pair of pliers (NOT ViseGrips and don't hold too tightly), and unscrew the Coil from the wire. It easier to do this than undoing the wire from the Coil.

6.       If you have new wires and Caps all moulded together, put the OLD rubber boot over the wire, with the wide end facing the end of the wire. Pull it up and peel it back so about 1-1 1/2 of Coil Wire are exposed.

7.       Inserting the point of the Coil Screw in the centre of the new Coil Wire, and holding the Coil Wire firmly (it should NOT be allowed to twist excessively) screw the Coil onto the on the new Wire until you feel the Wire butt up to the end of the Blind Hole in the Cap. (The Wire will start to turn with the Coil, at which point you should stop immediately - Do NOT try to overtighten.)

8.       Finally pull the rubber boot down the wire toward the Cap, until you can pull the boot over the new Cap. Repeat for the other Cap. That's it. You MIGHT like to test it before you start. See above for the testing procedure.

 

Coils

 

 

Technical Details about the Plug Caps:

 

 

 

 

NGK states:

 

 

While NGK Inductive Resistor Spark Plugs cost more than standard resistor plugs, they provide major benefits in late-model marine outboard applications.

 

Feedback/Opinions:

Note that SOME MODIFIERS of the Plug Caps have had success with 5kohm caps. Maybe if the leads are REALLY fragged, 5k caps will be an improvement. But since 1k is more desirable, the 5k might not function as well as that alternative. Note that 1 kohm is advisable as it is closer to the OEM resistance e.g. Trawl one out of a BMW 2002 or find an NGK source (See above). Some modifiers have had worse performance with 1 Good BERU Cap than 2#  5kohm NGKs.

  • This FAQ was compiled & edited by Kristian #562, non-electrical person extraordinaire. Special Thanks to the Nameless one and to Todd for his patience.Thanks to Shank for the extras)