The Enfield Bullet Manual

- by Pete Snidal (C)2003

Diagnosing Spark Problems

Do You Have Sparks?

Your engine needs a clean, bright, blue spark at the spark plug at the beginning of every power stroke. To determine whether this is being made available, the simplest test is to remove the plug -be sure to clean all dirt and grunge away from the region of the plug base before removing with a suitable spanner - and lay it on the cylinder fin beside the spark plug hole, with the heavy high-tension wire reconnected, and the plug base making good electrical contact with the cylinder fin. Then, with the ignition on, turn the engine over with the kickstarter, (gearbox in neutral) while observing the gap at the end of the plug. At each power stroke, you should see a bright blue spark at the plug tip.

If there is no spark, it's time to begin looking at the following:

The Fuse

If your fuse is not conducting, nothing electrical will work. No stoplight, turn signals, horn, or any lights, with ignition switch on or off. In this instance, first try replacing your fuse. Then, if still no joy, check the battery terminal connections and battery chassis ground for cleanliness. Disconnect the connections, buff up all surfaces with a piece of sandpaper - or a knife or screwdriver blade, or even a flat rock, and re-assemble. If you find that you have some electiral elements working - such as the lights or horn, proceed with the following ignition system tests:

  • 1. Faulty Spark Plug

  • 2. Faulty Ignition Points or Adjustment

  • 3. Poor Connection - 12V Circuit

  • 4. (Electronic Ignition) Faulty Module

  • 5. (Electronic Ignition) Faulty Reluctor

1. Faulty Spark Plug

A spark plug can be faulty due to "fouling" - the insulation portion of the tip - the part normally inside the combustion chamber - becomes coated or impregnated with electrically conductive foreign material - generally combustion biproducts - which "short out" the voltage pulses from the coil without producing a spark across the gap to ignite the fuel mixture on the power stroke. The test for this is obvious - replace the plug with your spare - you DO have a fresh spare in your toolbox, don't you? - and try with this known-good plug. If still no spark, look to the next step:

Faulty or Maladjusted Ignition Points

There are a number of steps involved in checking the ignition points. First, are they opening and closing when the engine is turned over with the kickstarter?

2. Checking Points Operation

Remove the cover of the contact breaker (behind the cylinder barrel - accessible from the left side of the machine). Using the compression release and the kick starter, rotate the engine, observing the points for opening and closing action. If they DO open and close, the next step is to check for burning and gap.

Once the points have reached their maximum opening, first examine them. With your screwdriver, pry the moving point away from the stationary one and check for burning or pitting of either of the point surfaces. (If there are any such signs, the points must be removed and dressed with a fine file and replaced - or replaced with your spare new ones. (I hope you have a spare set in your toolbox? Put away dry and safe in such as an empty 35mm film canister?)
If both point surfaces are clean and shiny, check the gap between them (at wide open) with a - .015 - ,4mm feeler gauge - you want a "just tight" fit. If not, adjust the opening by first loosening the fixing screw, (F in the photo shown), and, using a screwdriver inserted between the two dimples and the slot in position shown as A, adjust the point opening until the feeler gauge is just a tight slip fit between the points. Then tighten the fixing screw (F). Leave nuts labelled (T) alone - these allow rotation of the breaker plate to make adjustments in timing.

3. Checking 12V Primary Coil Circuit

The circuit path, from the battery, is through the following components: Checking the primary circuit is a simple matter of looking at the connection points of each component in turn, starting at the end and working backwards, until power is found. Presence of power is indicated by lighting of a test lamp, or, in cases of need, sparks.

Primary, but No Secondary Spark

This condition can be due only to one of four causes:

Cause
Solution
Shorted (fouled) spark plug Replace with Known-good plug
Coil High-Voltage (output) wire shorted or corroded Clean Wire - especially the ends
Excessive wet dirt/mud/dust on coil tower Clean coil tower and dry thoroughly
Faulty secondary winding in coil Replace with known-good coil

Primary Spark

The simplest and therefore first check of the 12V primary system is simply one of opening the closed points with the ignition on. Just rotate the engine until the points are closed, then turn on the ignition and pull the moving point open from the stationary one with an insulated tool, such as a plastic-handled screwdriver or dry piece of stick. (Although there is only 12V present, which will not shock you, the phenomenon of "inductance" and "back emf" can often wake you up!) You should see (and usually hear) a spark at the points on opening. Furthermore, when this Primary Spark occurs, a Secondary Spark should also occur at the plug, if it's still set up as described above.

If the primary spark thus produced does not produce a secondary spark at the plug, hold the spark plug connector wire (with the rubber boot pulled back if necessary, or a short bolt inserted into the connector) about 1/4"-6mm from the cylinder head, and twitch the points again. If you still get no secondary spark, either the coil secondary wire or the coil itself is faulty.

If you do get both sparks, then turn the engine over with the kickstarter - ignition still on - and look for the primary and secondary sparks as the distributor rotor opens the points on each revolution. If not, but spark occurs with physical manipulation of the points, re-set the contact breaker gap as describe above and try again. In extreme cases of getting the first but not the second, replacing the pointset with a new one may be necessary.

No Primary Spark?

If no primary spark can be induced, try rotating the engine until the points are open, then "shorting" the moving point to ground with a screwdriver contacting the point and the Contact Breaker body (watch that your shorting bar is insulated!) As you break the short circuit connection, you should see and hear a spark. If you do, but not with the points themselves opening, replace the points. If not, it's time to check the circuitry by moving back up the line.

The Coil Primary

For the following checks, you will need a test lamp, with one side grounded to the chassis, preferably the engine, and the other to the various test points.

First, check that there is power present at the coil primary terminal - the (+) one (generally White or Grey) - not the generally Black one not connected to the Contact Breaker. Use a test lamp, since jumping this to ground (ignition on, of course) will blow your fuse if the wiring is good. If there is power present here, with ignition on and points open (although the bulb should light dimly with points closed, if it's a low-draw test lamp), check for power at the other primary terminal - the black-wired (-) one. If you have power at the (+) terminal, and no power at the (-) terminal, with the points open and the ignition on, then the primary winding of your coil is burnt out, and the coil must be substituted with a good one.

No Power At Coil (+)?

If there is no power present at the coil (+) terminal, you may test the coil, the points, and the connecting wire between them by "jumping" a temporary connection directly from battery (+) to coil (+), then testing for spark at the plug with engine turning over as described in step 1 above. If this produces sparks, you may now firm up the temporary jumper connection and ride home to fix it properly later.

To fix it properly, later or on the spot, remove the jumper wire and continue to trace backward up the line for power. Next, after the coil (+), if no power is present, check the output of the last switch in line - eg. the ignition switch, on the Home or UK models. (see diagram - Home Models. If there is no power at this white wire on the ignition switch, (switch on and points open!) then check for power in at the switch - the Red wire from the battery fuse. If there is power at the input wire to the switch, but none at the output wire from the switch (red and white respectively), then the switch itself is faulty and must be replaced.

Indian (Home) Models - note that rubber snap connector C2 is a likely source of trouble, and is connected between the fuse holder and the ignition switch. Check the red wire in and out of this connector - or jump with a temporary wire directly from battery (+) to the Red Switch Input connection. (You will likely have to strip the insulation from the red wire in a small spot - or drive a pin through the insulation into the conductor inside to make a connection.)

The UK Models do not have this C2 connector.

North American Models - these models usually have a handlebar-mounted engine cutoff switch, which is fitted electrically speaking between the ignition switch and the coil input. see diagram If the cutoff switch has no output, check its input - the Brown/White wire from the Ammeter (+). If no power here, check the output from the ignition switch - also Brown/White, and if no power here, the Red Ignition Switch input wire from the fuse.

In all models, a temporary jumper wire direct from battery (+) to coil input terminal (+) will serve to test all elements of the system from battery to coil. If this cures a non-spark situation, there is something wrong "upstream" from the coil. If not, either the coil itself, or one of the "downstream" elements - connector wire or contact breaker points or internal connections - is bad. (This is assuming the battery ground connection is clean and good - indicated by lights and horn working.)

When you find input into an element of the system - a conductor wire or switch, but no output from that element, you have found the problem. Replace the faulty switch or if a conductor wire, "jump" it permanently with a known-good piece of wire, preferably of the same colour, and just tape it alongside the existing loom.

Electronic Ignition Systems

After-market electronic ignition systems, often considered very "upscale" by the techo/retro set (Old-Design Motorcycle Good; Old-Design Ignition system Bad! - Go Figure!) present a different set of challenges in the instance of spark failure. Since solid-state electronic/capacitor discharge ignition systems are difficult to impossible to repair on the road or in the (mechanical) shop, the wise owner will pack a spare "magic box" and reluctor (the little coil in the CB housing) with his riding spares, since replacement with a "known-good" spare is the only reliable way to verify functionality. (Or not.)

There are, however a few other possibilities which may be investigated:

If the above considerations are met, and there is still no spark, replace parts with "known-goods" until the spark returns. When it finally comes back, discard the last part you replaced - and be sure to replace your replacement spare with a fresh one for next time!

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