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The when why and how on replacing your coils Print E-mail

XS11 Ignition Coils FAQ

by Mike Saar, edited by JP Honeywell

How do I know when I need to replace my coils?

You may notice that the engine is not running well. It bogs down and produces only a fraction of its normal power.

As you know, you need three things to make an engine run. Correct fuel/air mixture, proper compression and (good) spark coming together at the right time. If all three are not there, it will not run.

Here we will only deal with the spark (or the lack thereof).

First, let's check a few things. Is the battery fully charged and in good condition? Is the electrolyte level between the high and low markers? No cracks, sulfation or other damage? Are the contacts clean and free of corrosion? Remove your battery and take it to Trak Auto, Pep Boys, etc. and they will test your battery with a load charger for free to make sure it is okay.

Next, are the fuses good? Visual inspection of a fuse is not good enough. Sometimes a fuse opens at either end under the metal cap and you cannot see that it is open. Test them with a Volt/Ohm Meter or continuity tester to make sure that the fuse is not blown. [The fuse panel is a known deficiency on XS 1100 motorcycles. It would be wise to replace the fuse panel as described in the two articles in the Modifications section of Tech Tips.]

Now check the spark plugs. A bad or broken spark plug can cause similar symptoms. Make sure that the plugs are gapped properly and are clean. If in doubt, replace them, as they are cheap and should be replaced as part of routine maintenance.

Is there fresh gas in the tank? Are the petcocks turned to run or prime? Is the fuel/air mixture getting to the cylinders?

If all that checks okay then let's get down to checking the coils.

Check that the primary wiring (the small wires attached to the coils) attachment points are all clean and free of corrosion. While you are at this point you can also check the resistance of the primary and secondary sides of the coils with a volt/ohm meter.

Working with one coil at a time, trace the small wires (these are the primary wires), from where they enter the coil back to where they connect to the wiring harness. There should be two per coil (a solid orange or solid gray one and a red/white striped one). Pull these connections apart and clean with electrical contact cleaner if necessary. Protect the connection after cleaning by applying di-electric grease to the connectors. Pull the spark plug wires for that coil off the plugs. Measure the resistance across the wires coming from the primary side of the coil. It should read 1.5 ohms ± 10%. The Yamaha manual says these measurements are made at 68 degrees Fahrenheit (20 degrees Celsius). With those connections still apart you can test the resistance of the secondary side of the coil. Measure the resistance across the two spark plug connectors. This measurement should be 15k ohms ± 10% at 68 degrees F. (20 deg. C.). If either of these readings is infinite resistance or past the ± 10% mark, you probably need to replace the coils.

If the readings are marginal, you still may not be out of the woods. I had a set of stock coils where one coil measured well within specifications and the other was marginal. The marginal coil worked until it warmed up. Then a bad wire inside warmed up enough to separate and the coil would stop working. Instant XS-ively bad attitude. I could go about 7 miles before having problems. I could get it home if I waited 20 minutes for the coil to cool down and start working again. I'm told that this normally does not happen. Usually either a coil works or it does not.

Previously, it was believed that the spark plug wires are not replaceable on stock units, and that you must replace the whole coil assembly. This has now been proven to be false. A repair tip shows how to replace the spark plug wires which I speculate are, more often than not, the real failure (and not the coils themselves). If an inspection of the spark plug wires shows visible damage such as cracking, checking, badly worn spots (from rubbing against something) or cuts in the insulation, they need to be replaced. Note: Even wires with no apparent damage can have failed. Such damage shows up as intermittent misses while running. Electricity follows the path of least resistance. If it finds a path where it can arc to the frame or engine easier that going to the spark plug, it will. This path could be through a damaged spark plug lead. This can cause severe damage to the electronic ignition module or physical harm to you and/or your bike.

If the secondary leads are not damaged, there is another test you can do involves pulling the spark plugs one by one, cleaning them and checking the spark.

This is best done by two people and in dim light. One person will start and stop the engine and the other will control the spark plug and make observations.

Remove one spark plug at a time and connect it back to its spark plug wire. Hold the tip of the plug against a good ground on the engine. IMPORTANT: Be sure this is a good bare metal spot on the engine! Then, with the transmission in neutral, turn the key on and press and hold the start button while you observe the spark. It should be a good fat blue/white spark. Chances are that the engine won't start. If it does, do not panic, just shut it down with the kill switch. (Warning: Please use this procedure with extreme caution. You can receive several shocks of electricity (18-20kV) from the coil if you do not ground the plug to the engine block properly. You must also try to keep the firing spark plug away from the open spark plug hole. The sparking plug could ignite any air-fuel mixture forced out of the engine when you turn the engine over.)

Now that I know that I need new coils, what are my options?

Options are:

Stock coils. Benefits are exact replacement. Take out the old coils and replace with the new. Drawbacks are more expensive than the alternatives, limited availability, and replacing spark plug wires is slightly more difficult. (Check out the repair tip to see how to modify the coils.)

10/23/00 Update by Gary Granger

  • Yamaha factory coils:

    I found was that factory coils for the 78-80 XS's are no longer made by Yamaha, but that does not mean that you can't get lucky and find some in stock at a dealers shop. According to Zanotti's Yamaha) the part numbers are 2H7-82310-60-00 and 2H7-82320-60-00 for these coils. But the coils for 81's are still available from Yamaha as of 7/00 and are a little smaller, but by all accounts, will work well and fit nicely. But they do have the higher primary resistance of 3 ohms. From Zanotti's these were less than $100 for the pair. If you call Zanotti's, be sure to as for the "Internet price" and you'll get a bigger discount.

Aftermarket coils by Accel or Dyna. Benefits are improved power, easier starting (may be relative to defective coils or plug wires), replaceable spark plug wires and in many cases better gas mileage. The drawback is that the coils are larger than stock and do not fit in precisely the same location. It could take a bit longer to figure out the mounting bracket modifications than with stock coils.

10/23/00 Update by Gary Granger

  • Accel coils:

    You can get replacement coils from Accel, but they do not have the proper primary resistance per the manual, (for 78-80 XS applications only). Also the part number given in the Coil FAQ is wrong according to ACCEL. I have not verified the correct part number yet but one person who bought a kit said it was Accel #140403. The correct kit is listed in Dennis Kirk and is #20-309, and comes with brackets, hardware and plug wires and runs about $148 USD. Every person who contacted me said that installation took some time and work to make the brackets fit OK. Several people contacted me about Accel coils on their bikes and all of them were using the the coils for "non CDI ignitions", these coils have a primary resistance of 3 ohms. This is also the primary resistance of the 81 and 82 bikes with the 4RO type ignition box. So they should work on those bikes as well.

    Dyna coils:

    Dyna also makes a coil that should work on the 78-80 XS. It has the proper primary resistance of 1.5 ohms and should work. I called Dyna since the coil was listed as a "6 Volt" coil in Dennis Kirk. The guy told me that coils are not really voltage rated and that the coil kit will work in 12 volt systems. I think it has something to do with racing applications that tell you to hook the coils primaries in series for dual plug applications (according to Dyna's web site and the Dennis Kirk catalog) and so you would only have 6 volts accross each coil. Dyna Part number is DC2-1 (Dennis Kirk #20-265) and is for two double tower coils. These do not come eith any brackets or wires and current prices were $114 - $118 USD from the major catalogs.

I decided to go with aftermarket coils. What do I need to know about installing them?

I only have experience with installing the Accel coil kit (number 72-0100) on my Yamaha XS1100SH but I imagine the Dyna set is similar. There have been questions on the list about some sort of resistor that comes with some kits. There was no such resistor with the Accel coils and no mention of it in the installation instructions that came with the kit for my bike.

The replacement procedure is quite straightforward. First, remove the seat, disconnect the battery, and remove the gas tank and any thing else that may be in the way (fairings, horns, etc.).

These out off the way, note routing of all wiring relating to the coils. There should be two small wires (these are the primary wires or leads) and two large wires connected to the spark plugs (these are the secondary wires or leads also called spark plug wires).

It is very important that you wire your new coils the same way as the old. If you do not, the bike will not run.

The small (primary) wires feed electricity to the coil at a certain time enabling a magnetic field to build up. Then when the electricity is shut off, this field collapses. When the field collapses it causes a high voltage charge to go out through the two towers on the coils. The spark plugs, connected to those towers via the secondary leads, fire a spark across their electrodes causing ignition of the compressed air/fuel mix. If any of the wires are connected to the wrong coil, the wrong plug will fire and nothing much will happen. Remember, spark + air/fuel mix at the right time equals ignition.

So, following the installation description supplied by the manufacturer, let's swap out the coils working on one coil at a time. This makes things less confusing.

First, loosely assemble the secondary (spark plug) leads. The plug wire part of the kit comes with some bright yellow 8.8mm graphite suppression core wire and four each of coil terminals, coil terminal boots, spark plug terminals and spark plug boots. The terminals and boots can be loosely fitted to the wires and then attached to the coil for fitting the coils to the bike.

Remove a stock coil from its mounting bracket. Unplug the two small (primary) wires from their connectors on the bike. I re-used these wires by clipping them off close to the coil. I then stripped about 1/4" of insulation of the cut end of the wire and crimped a round lug connector onto the wire. I then attached these wires to the Accels coils primary terminals with the supplied hardware. You could save your coils (if you are just doing an upgrade) and get the right connectors from the local auto parts store. Just take the coil with you and match the connectors and the wire gauge to make new wires.

You should, I think, mount the new coils in as close as possible to the same position as the original stock coils. On my XS1100SH I used a single longer bolt through one original mounting points to mount one end of the Accel mounting brackets and an Accel mounting ring clamp on the other end. There is some room for fine adjustment once both coils are mounted into place but not tightened down. This allows for adjusting the coils so that the two towers do not contact frame per Accels mounting instruction page.

Another way to mount the new coils, if the above procedure doesn't work for you, is to mount the coils directly to the frame using 3-1/2 inch hose clamps. If you place the hose clamp between the towers and tighten it securely it should be as secure as the clamps provided with the coils. Again, be very sure that the towers *with the plug wires attached* do not contact the frame.

Accel cautions you with a separate instruction to be sure that the plug wire towers *with the wires installed* do not come in contact with the frame, gas tank, or any other component. Accel will void the warranty if they find vibration damage from poor mounting so be careful.

Repeat this mounting procedure for the other coil.

Once you have everything in place, fit your gas tank, fairing, and whatever else was originally removed back on to be sure nothing contacts the towers. If everything checks out, take the tank back off and use Locktite on the coil mounting nuts/bolts and tighten them. Accel also says to go back and check all the hardware for tightness after 200 miles.

After positioning the coils correctly and tightened down you get to cut and assemble the secondary or spark plug leads.

You need to cut the yellow 8.8mm spark plug wire to length for each plug. The length should be long enough to prevent any stress on the wire when it is hooked up between the coil and the spark plug. I loosely fit the coil end connector onto the wire then fit the wire onto the correct coil tower. I then used enough wire to get comfortably to the corresponding spark plug. The wire kit instructions say to leave an extra inch on each end of the wire for attaching the connectors. I also left an additional inch (just in case).

The connectors are crimped on using a hammer and the supplied "anvil" which consists of two pieces of 1/4" steel shaped to crimp the connectors around the wire. Following the directions given on the spark plug wire sheet, you first strip away about 1/2 inch of the insulation from around the core of the yellow 8.8mm plug wire. You must be very careful not to damage the core. You then bend the core over the edge of the insulation and back along the side of the insulation. Then slide the proper connector on so that the core wire is between the connector and the insulation. The connector is then placed in the "anvil" which is stuck with the hammer until the edges of the anvil meet. This crimps the connector, core and insulation together making for a very solid connection that is almost impossible to pull apart.

You will also find than you now need to save those spark plug tips you have not used in the past. The Accel spark plug connectors are shaped to clip onto those and not on the screw threads.

Wire the spark plugs per instructions and reset your spark plug gaps to .035". This is just .003" wider than the stock .023-.032" but remember that you are also dealing with a much hotter spark. Stock coils put out somewhere around 15-18kV where the Accels put out closer to 40kV per Accels packaging.

Now, you can put back all the stuff (horns, fairing, brackets, etc.) that you took off. Put the gas tank back on, hooking up the gas and vacuum lines, hook the battery back up and put the seat back on.

Accels instructions also say "As Accel's coils are quite powerful and deliver a much stronger spark than original equipment coils, considerable care should be taken after [the coils'] installation to be sure the carburetor jets on your model are adequate."

I have not had to change the jets in my carburetors. My personal experience has been a light gray/tan spark plug firing tip every time I've checked indicating neither rich nor lean conditions. As with any change involving the intake, exhaust, ignition or carburation systems you should keep an eye on your spark plug tip colors. If they start leaning to the white side of the color range you are running lean and should enrichen the mixture for that cylinder until the plug color is a light tan.

An amateur racer friend of mine told me about a test, called a spark plug chop, he picked up at the track. It checks how lean or rich your carburetors are actually running at speed. First, put new spark plugs into the bike and pack a spark plug wrench, a note pad and a pen into your pocket. Then you warm up your engine to normal operating temperature (hmmm, sounds like a great excuse for a 15 minute ride to me). Then find a nice open stretch of road with little or no traffic. Here is where it gets fun. Get your speed up to your normal cruising range and keep it there for a minute or two. Then without chopping the throttle, hit the kill button. Be careful and make sure you are away from traffic when you do this. Your rear wheel wont lock up, you should just slow down a bit faster than if you chopped the throttle. Pull in the clutch and shift into neutral. Stop the bike and pull one plug, check it's condition taking careful note of the tip color. If it's very light gray or white, you are running lean. Light tan to medium light gray, it's just about right. Dark gray, dark brown or sooty black means it's running rich. Check each of the plugs while you are stopped and write your findings down on the note pad. You will need this later if there is any rejecting to be done to the carburetors.

You can and should use this test every time you make a change in air intake, carburetion or exhaust systems as all of those effect how the engine uses fuel.

The usual disclaimer, YMMV, quite literally applies.

 

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