Custom Motored Bicycles

Stock spark plugs have a larger tip that needs to be removed before use with the sparkplug boot.

NO SPARK? To check your MAGNETO and CDI, Try this:

MAGNETO:

 Use Low Ohm-Meter Scale About 200 Ohms 20K
1) Check Ohms between BLACK wire and WHITE wire. Reading should be around 2 Ohms
2) Check ohms between BLUE wire and WHITE wire. Should be around 300-400 ohms.

CDI:
Use Ohm Meter High Scale About 200-K
1) Positive lead on BLUE wire and Negative lead on BLACK wire should read infinite (no activity)
2) Positive lead on BLACK wire and Negative lead on BLUE wire. Should be about 130-150 K-ohms
3) Positive lead on Spark Plug wire and negative lead on BLUE wire. Should read between 135-155 K-ohms

Switch to Low Scale 20K
4) Measure between Spark Plug wire and Black lead. Should be about 2.5 - 2.7 K- ohms

With the meter set to ohms, put your meter on the blue wire and a frame ground, you should have around 300 ohms or more, check the white wire to ground on the frame should be around 2.5 ohms do these with the CDI “disconnected.”

Weak spark or no spark:

To check if you are receiving power to the spark plug, follow these simple steps.

1. Remove the spark plug from the cylinder head.
2. Re-attach the spark plug to the spark plug cap.
3. Lay the spark plug on the cylinder head so that the metal of the plug is touching any metal portion of the cylinder head. DO NOT HOLD THE SPARK PLUG OR BOOT BY HAND.
4. With the clutch out, push the bike forward or turn the rear wheel. A bright spark should be visible.

If no spark is visible:

• Double check the connection of the wires, particularly the blue to blue and black to black.
• Check that no particles are lodged between the side and center electrodes of the spark plug.
• Try replacing the spark plug or cleaning it by running sand paper through the side and center electrodes and resetting the gap to 0.038".
• Re-test for spark with the kill switch pressed in. Try feathering the kill switch. Disconnect the white wire completely allowing the wire to hang free, then re-test the engine.
• Magneto Testing- Take a voltmeter or multimeter and adjust it to the Ohms setting at 20k. Ohms measures the resistance across a circuit. Check voltmeter across the following wires:
  • Blue wire to the White wire of the magneto.  The resistance should be 0.25 to 0.40. New magnetos read 0.31.
  • White wire to Black wire should read 0.0.
  • Blue wire to Black wire should read close to 0.31.

If your reading is far off from this, then the magneto is to blame for bad spark.

• CDI Testing- Run the voltmeter at the same 20k setting. Check voltmeter across the following wires:
  • From the inside of the spark plug boot to the Black wire of the CDI. Your reading should measure 2.0 - 2.7.  A new CDI will read 2.3.
  • Spark Plug Boot to the Blue wire there should be no change, or 1.0.
  • Blue wire to Black wire there should be no change, or 1.0.

If the resistance is different than specified, this simple test will tell you where your problem lies.

Helpful tips

Consistently running at full RPM is about the worst thing that can be done an engine long term. Always running at full throttle does not leave enough time for the oil mixed in the gas to circulate around the engine and lubricate the cylinder wall and lower engine bearings.

If you are going to run at high RPMs, do a plug check. Pull the spark plug once in a while and see what color it is. If your plug is tan, white, dry and clean, then you need to either slow down, not ride for so long, and/or increase the oil/gas ratio. If your plug is black and moist, then you're doing well. Even better is if a little black drop occasionally falls from the exhaust tip.

If your spark plug is black, dry, and sooty, then it may be time to clean the combustion chamber. "Decarbonisation" was a common maintenance procedure in the days when British motorcycles roamed the streets and leather clad rockers owned the roads. You need to keep a clean environment in the combustion chamber. With high mile heavy use (5,000 miles+), we do see a build up of carbon beneath the cylinder head and on the combustion chamber. If the carbon buildup is thick, this barnacle-like substance can cause a piston seizure if any small piece breaks off and lodges between the piston and cylinder wall.

To "Decarbonise" an engine, remove the 4 nuts on top of the cylinder head, remove the cylinder head and metal head gasket. Bring the piston to the top of its stroke. Using sand paper or a soft wire wheel, remove the carbon from the top of the piston crown and the bottom of the cylinder head. Be careful not to score any of the inner surfaces.

And remember...
FOREIGN PARTICLES ARE THE ENEMY! Clean your air filter often.

Chinese CDI units do not like to get frozen or wet.

Have many motor internal parts please call if you need a certain motor part. Thanks Lynn 414-732-0017

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Magneto Testing - Take a voltmeter or multimeter and adjust it to the Ohms setting at 20k. Ohms measures the resistance across a circuit. Check voltmeter across the following wires:
Blue wire to the White wire of the magneto. The resistance should be 0.25 to 0.40. New magnetos read 0.31.
White wire to Black wire should read 0.0.
Blue wire to Black wire should read close to 0.31.

If your reading is far off from this, then the magneto is to blame for bad spark.

CDI Testing - Run the voltmeter at the same 20k setting. Check voltmeter across the following wires:
From the inside of the spark plug boot to the Black wire of the CDI. Your reading should measure 2.0 - 2.7. A new CDI will read 2.3.
Spark Plug Boot to the Blue wire there should be no change, or 1.0.
Blue wire to Black wire there should be no change, or 1.0.

NGK B5HS spark plugs cross reference chart

NGK STK: 4210
Accel: 156
AC Delco: 45F
Autolite: 2656
Champion P/N: L90C
Champion STK: 896
Denso P/N: W16FS-U
Denso STK: 3034
GM OEM NR: 5612095
Prestolite: 1,40E+004
Valley Forge: 134

NGK B6HS spark plug cross reference chart