Tip & How-To about Motorcycles

How to test a motrcycle twin ignition coil

To test a twin ignition coil on a motorcycle you will need a pocket multimeter.
With the meter set to kilo-ohms(1000 ohms) scale,place one test lead into one spark plug cap & the other test lead into the other plug cap.(this is called the ignition coil secondary resistance) The reading should be around 20-40kilo ohms.
If a high reading exists check again with spark plug caps removed(they un screw from the lead) then check caps seperate. Caps typically read 5 to 10 kilo-ohms.

A faulty plug cap is not as un-common as you might think.

To test ignition coil primary resistance set the meter to ohms(lowest scale) Place one meter test lead to the small wire going into the coil & the other test lead onto the coils body(where its metal) The reading should be only 2 to 5 ohms.

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what does the code B1141 mean


Hi Helodrvrh60, perform the following tests:
1. Fill acid type batteries to proper levels.
2. Charge battery overnight at 1-2 amps you need 12.5 volts or better after charging.
3. Hook up battery positive cable, then with your multimeter on the milliamp scale connect one lead to the negative battery post and the other lead to the ground cable. Meter should read 3 milliamps or less, 10 milliamps with a radio, 15 milliamps with radio and CB. If your meter reads higher you need to isolate the circuit by pulling fuses and circuit breakers one at a time and observe meter for drop in aprerage then get out your test light and track down the short in that circuit.
3. Make sure all connections are clean and tight especially the negative cable at "BOTH" ends.
4. Hook up volt meter to battery and start engine, if meter falls below 9.5 v while cranking replace battery.
5. With engine running at 3600 RPM battery should read 14.3-14.7 volts if not continue tests.
6. Unplug voltage regulator from alternator at crankcase by front of primary cover.
7. To test voltage regulator go to: https://www.youtube.com/watch?v=F8EjV0IjW9Q
8. With ohm meter, one lead grounded, touch alternator pin meter should read infinity, if not replace stator.
9. With ohm meter, both leads touching alternator pins meter should read 0.1 to 0.2 ohms on 1989 and later models. 0.2 to 0.4 ohms 1988 and earlier models, if not replace stator.
10. With volt meter set on AC scale, both leads touching alternator pins meter should read
16 to 20 volts AC for every 1000 RPM'S 1989 and later and 19 to 26 volts AC for every 1000 RPMS. If not replace rotor.
17. For a free wiring diagram please visit the website below. Good luck and have nice day.
Harley Davidson Wiring Diagrams and Schematics
Big Twin Carb EFI DTC Intructions codes Harley Davidson Forums Harley...

Jun 28, 2012 | Harley Davidson Motorcycles

1 Answer

looking for a wiring diagram for 2003 Heritage.


Hi Ernie, perform the following tests:
1. Fill acid type batteries to proper levels.
2. Charge battery overnight at 1-2 amps you need 12.5 volts or better after charging.
3. Hook up battery positive cable, then with your multimeter on the milliamp scale connect one lead to the negative battery post and the other lead to the ground cable. Meter should read 3 milliamps or less, 10 milliamps with a radio, 15 milliamps with radio and CB. If your meter reads higher you need to isolate the circuit by pulling fuses and circuit breakers one at a time and observe meter for drop in aprerage then get out your test light and track down the short in that circuit.
3. Make sure all connections are clean and tight especially the negative cable at "BOTH" ends.
4. Hook up volt meter to battery and start engine, if meter falls below 9.5 v while cranking replace battery.
5. With engine running at 3600 RPM battery should read 14.3-14.7 volts if not continue tests.
6. Unplug voltage regulator from alternator at crankcase by front of primary cover.
7. To test voltage regulator go to: https://www.youtube.com/watch?v=F8EjV0IjW9Q
8. With ohm meter, one lead grounded, touch alternator pin meter should read infinity, if not replace stator.
9. With ohm meter, both leads touching alternator pins meter should read 0.1 to 0.2 ohms on 1989 and later models. 0.2 to 0.4 ohms 1988 and earlier models, if not replace stator.
10. With volt meter set on AC scale, both leads touching alternator pins meter should read
16 to 20 volts AC for every 1000 RPM'S 1989 and later and 19 to 26 volts AC for every 1000 RPMS. If not replace rotor.
17. For a free wiring diagram please visit the website below. Good luck and have nice day.
Harley Davidson Wiring Diagrams and Schematics
Big Twin Carb EFI DTC Intructions codes Harley Davidson Forums Harley...

May 31, 2012 | 2003 Harley Davidson FLSTC Heritage...

1 Answer

I have a 05 HD sportser xl1200c. when key is in ignition and turned to acc speedo lights up. turn to ignition . all lights die..


Hi Jeffcrippen, perform the following tests:
1. Fill acid type batteries to proper levels.
2. Charge battery overnight at 1-2 amps you need 12.5 volts or better after charging.
3. Hook up battery positive cable, then with your multimeter on the milliamp scale connect one lead to the negative battery post and the other lead to the ground cable. Meter should read 3 milliamps or less, 10 milliamps with a radio, 15 milliamps with radio and CB. If your meter reads higher you need to isolate the circuit by pulling fuses and circuit breakers one at a time and observe meter for drop in aprerage then get out your test light and track down the short in that circuit.
3. Make sure all connections are clean and tight especially the negative cable at both ends.
4. Hook up volt meter to battery and start engine, if meter falls below 9.5 v while cranking replace battery.
5. With engine running at 3600 RPM battery should read 14.3-14.7 volts if not continue tests.
6. Unplug voltage regulator from alternator at crankcase by front of primary cover.
7. To test voltage regulator go to: https://www.youtube.com/watch?v=F8EjV0IjW9Q
8. With ohm meter, one lead grounded, touch alternator pin meter should read infinity, if not replace stator.
9. With ohm meter, both leads touching alternator pins meter should read 0.1 to 0.2 ohms on 1989 and later models. 0.2 to 0.4 ohms 1988 and earlier models, if not replace stator.
10. With volt meter set on AC scale, both leads touching alternator pins meter should read
16 to 20 volts AC for every 1000 RPM'S 1989 and later and 19 to 26 volts AC for every 1000 RPMS. If not replace rotor.
17. For a free wiring diagram please visit the website below and good luck.
Harley Davidson Wiring Diagrams and Schematics

Aug 25, 2011 | 2005 Harley Davidson XL 1200 C Sportster...

1 Answer

missing on front left cyl. popping when you give it gas left front plug is clean and wet check fire and it is strong and blue compression is good


G,day. If only the L/H front cylinder is the problem & compression is good then the most likely possable causes of your problem are - A open circuit spark plug cap on that cylinder or a carburettor fault(blocked jet) on that cylinder(or carby balance setting).I would suggest testing the ignition coil secondary resistance.Do this by removing plug caps from cylinders 1 & 4. Set multimeter to kilo ohms(ohms x 1000) .One test lead to one plug cap- other test lead to other plug cap(do not allow probes to touch your fingers-touching both test probes whilst undertaking this test will give a false reading).reading should be 10 to 20kilo ohms.If open circuit-remove plug caps from leads( they unscrew)and test caps seperate. Should read 5 kilo ohms. Replace if open circuited(This is a common problem on all road bikes).If that sounds to difficult, any good motorcycle shop should be able to check them while you wait.It only takes a few seconds.Sorting the carbies without experience is very tricky.Have the carby balance & mixtures checked first in case its just an incorrect setting before pulling off & cleaning the carbies.
Hope this is helpfull
Regards Andrew Porrelli

May 11, 2011 | 1981 Honda GL 1100 Innerstate Gold Wing

1 Answer

Hi can you tell me the firing order for 87 gpx 750. Regards Paul


The firing order on your bike is 1,3,4,2. These bikes use what is called a wasted spark system. They fire whenever the piston reaches top dead centre.
That is to say they fire on top dead centre compression as well as top dead centre rock-over( exhaust/inlet ). Each coil has two leads on them.
The left coil goes to number 1 & 4 cylinders.
The right coil goes to number 2 & 3 cylinders.

The GPX 750(like most road bikes) have a resistor type spark plug cap on them that was prone to cause problems.

To test the coils/caps, use a multi-meter to test their secondary resistance.

To do this set the meter to kilo-ohms(1000 ohms), place one meter probe in one plug cap & the other probe in the other plug cap( i.e. 1&4, 2&3 )

The meter should read 10kilo-ohms to 15 kilo-ohms.

If it reads higher than that try un-screwing each cap & test the coils with the caps removed by probing the leads. If the coils(without caps)read about 5 to
10 kilo-ohms, check the caps.
The caps should read 5 kilo-ohms each.
It is very common to find these open-circuited.
Replace any open circuit caps.

I hope this has been of some help.
Otherwise if you can be a little more spacific with your problem I will try to help further.

Regards Andrew Porrelli

Jan 28, 2010 | 1987 kawasaki GPX 750 R

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