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<HTML><center><span style=“font-size:180%;text-align:center;font-weight:bold;”>It won't spark! Now what?</span> <BR><span style=“font-size:120%;text-align:center;font-weight:bold;”>by DonTZ125</span></center></HTML>

I'm surprised it's taken me this long to come up with this, but I can be a lazy SOB when I (don't) put my mind to it. There have been many inquiries, here and on the Archives, from people who aren't getting a spark. The first impulse when seeing the 17th inquiry in a particular month is to cry “RTFM!”, followed closely by “Use the f'n search!” With that out of my system, I will acknowledge that the manual is a) difficult to read sometimes and b) not readily to hand in all garages; that, and the search systems on both sites suck to greater and lesser degrees.

<html><span style=“color:red;font-size:120%;text-align:center;font-weight:bold;”>Usual disclaimers apply. This guide is intended to assist the shade-tree mechanic, and is in no way idiot-proof.</span></html>

Ok. You've pulled your #3 & 4 caps off, unscrewed the spark plugs, re-inserted the plugs into the caps and set them on the head such that the plugs are grounded. You turn the engine over, and … no spark.

First thing to check is your battery. The ignition system fires wasted spark (every 360 degrees of crankshaft rotation, #1 & #4 spark simultaneously, 180 degrees later #2 & #3 spark together = four sparks per revolution of the crank) and is very power hungry. It is quite common for a tired battery to be able to turn the starter motor but have nothing left for the coils.


  • Check that the cells are full and the plates aren't warped. Top up with distilled water if necessary.
  • Check static (off) voltage (>12v). Charge if necessary (off the bike). Top up cells if necessary.
  • Check that the battery terminals are clean and tight.
  • Ensure the battery as a whole is clean, with no acid crystals, dirt or crud. A dirty battery can slightly short the positive and negative terminals causing the battery to slowly drain itself.

Plugs, caps and leads

  • Switch off!
  • Remove the other plugs. Inspect your plugs for fouling; they can be cleaned with blasting or burning (a lighter won't do it). Wet plugs can be dunked in solvent. Clean, fresh plugs are cheap and easy insurance, and one less thing to screw up your checks.
  • Check the electrode gap (0.7-0.8mm) and the condition of the electrode. Replace or adjust if necessary.
  • You've already got the caps out in the open, may as well inspect them. Give the caps a tug; if they pop right off, that's a problem. Otherwise, unscrew the caps from the leads. Measure the resistance of the caps (9k-11k ohms). Replace if necessary.
  • Inspect the ends of the leads; if the copper strands are green, or if there's more rubber than copper in view, trim the lead in question back about 1/4“.
  • Measure the resistance across each pair of spark leads - 1 & 4, 2 & 3 (9.6k-14.4k ohms)
  • Re-install the caps and leads, check for spark.

Didn't work? Ok, next step - pull off your tank or tank cover and rider's seat.

Coils and wiring

The FZRs have 12 Volt coils, so anything less than 12V delivered to them = a weak spark or no spark at all. When the starter is engaged the voltage delivered drops, but should still be above 10V. Corroded connections can and will reduce the voltage, seriously affecting the bike's ability to fire up.

  • Take a reading of the battery voltage
  • Find your coils. Turn the key switch and kill switch ON. Measure the voltage (versus battery ground) to both coil low-tension inputs (Red/White wires) at the coil solder joints. Anything more than a 0.5v drop from battery voltage can cause a weak or no spark.
  • If the voltage drop is greater than 0.5 volts a likely cause is a loose or dirty ignition connector (located close to the radiator filler cap - Red and Brown wires), and / or the coil low-tension connectors. Clean and check the connectors if needed.
  • Switch off!
  • Find your coils, and unplug the low-tension connectors. Check the resistance across each coil-side connector - Red/White wire to Grey or Orange wire (1.8-2.2 ohms). Note that this is very low, and errors in the instrument can affect the reading. Be sure to zero your multimeter before taking these readings. Reconnect the coil wiring. Replace the coil if out of spec.
  • Disconnect the battery negative cable (black).
  • Disconnect the battery positive cable (red).
  • Find the TCI / ignitor box. There are generally 2 large connectors. If there is a (4-pin or 8-pin) plug on the left and a 6-pin connector on the right, unplug the 6-pin connector. If there is a large 13-pin connector, unplug it.
  • Turn on the key switch and kill switch.
  • Check for continuity between the Orange wire and the battery positive (red) cable. Inspect and correct wiring if no continuity.
  • Check for continuity between the Grey wire and the battery positive (red) cable. Inspect and correct wiring if no continuity.
  • Switch off!
  • Unplug the left 4-pin or 8-pin connector, if present. Check for resistance between the top-right and top-second-from-right (for 8-pin connector, looking at pins, wires away), between top-right and top-left (for 4-pin), and between bottom 3rd from left and 4th from left (13-pin connector, looking at pins, wires away). This is from the crank signal pick-up coil; wire colors are usually White/Red & White/Black. (80-120 ohms). Inspect and correct wiring if no continuity.
  • Check each coil signal wire for continuity for ground. Any continuity indicates a short in the wiring or in the coil itself and must be corrected.
  • Check the pick-up coil (behind the generator cover on the FZR250, 400, 600) for debris or fouling. Any foreign objects on the signal pick up coil will badly disrupt the signal; clean as necessary.
  • Reconnect the TCI plugs. Reconnect the battery positive and negative cables. Check for spark.

If the bike is cranking, the safety system SHOULD be satisfied, but it is possible that the wiring between the main relay and the TCI is loose or damaged.

Safety system

  • Switch off!
  • Check for continuity between the battery negative terminal and the center-top wire (6-pin connector) or the bottom second-from-left wire (13-pin connector, looking at pins, wires away). This is your safety signal. Inspect and correct wiring if no continuity. The main relay assembly (diode block on the FZR400) may require cleaning or replacement.
  • Check Neutral , Clutch, and Side-stand switches for security and function.
  • Check for spark.

At this point, pretty much all that's left is the TCI. You can swap out a known good box to confirm the system works, but there really isn't a test to confirm that the ignitor works. (I plan on developing a tester sometime in the medium future). If the fuel pump primes when the key and kill switches are turned on, the TCI may have damaged ignition drivers but is likely repairable. If you have no spark and no pump, the outlook is generally poor.

Potentially dangerous check to confirm the coils and plugs really do work

  • Switch off!
  • Unplug the 6-pin or 13-pin connector from the TCI.
  • Find and cut two 12” lengths of 16ga wire, and strip 1/4“ from both ends.
  • Connect one wire to the Orange wire terminal on the connector.
  • Connect the other wire to the Black wire terminal on the connector.
  • Ensuring the wire ends are not touching, turn on the key and kill switch.
  • Strike the two free ends together smartly like you were lighting a match. Have a helper watch for spark at the spark plug.
  • Switch off, move the wire on the Orange wire terminal to the Grey terminal. Turn on the power, and repeat the check.
  • Switch off, remove the wires, and reconnect the TCI plug(s).

What happens if you have spark on some cylinders, but not others?

This is a better situation than 'no spark', since it means that almost everything is working!

  • Spark failure on a single cylinder is almost always due to a loose, damaged, or out-of-spec cap, lead or plug - everything upstream of the spark lead has to work for the OTHER cylinder to spark. It is entirely possible that a mis-jetted carburetor will foul the plug and cause loss of spark, but this will become obvious as soon as you replace the plug!
  • Spark failure on paired cylinders (1-4 or 2-3) is generally the coil or low-tension leads, or the TCI coil driver transistor. It could be a coincidental 'single cylinder' failure (above) of both cylinders. Unplug and swap the two low-tension connectors. If the spark stays on the same plugs (1-4 was sparking, 2-3 wasn't, and it stays that way), both TCI drivers work but the coil, high-tension components or low-tension wiring is bad. If the spark changes to the other set of plugs, then the TCI coil driver is fried. Don't forget to swap the low-tension connectors back to their proper spots!
  • Spark failure on two non-paired cylinders (#1 and #3) is coincidental, and should be treated as 'single cylinder' failures as above.
no_spark_now_what.txt · Last modified: 2020/10/19 11:51 by