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Very poor power; test ignition with multimeter

roeme

roeme

Forum Mentor
Past Site Supporter
The 550 I'm currently riding got some electrical gremlins which I partially got out ? I still have a as-good-as-dead battery to replace.

However, I fear since I ride it all the time (hey, I got lights and can kick'er) the remaining gremlins new relocated to the ignition; today she hung onto the choke for a ridiculously long time; and the engine developed next to no power. I strongly suspect she's running only on two cylinders.

I want to make sure that the ignition is okay before moving on to other things. The manual only refers to some 'electro tester' [sic] to test the coils.

How can I test the coils with a multimeter on hand?

Also, I would like to check wether I get a spark at all, but I'm not too sure on how to go about it. I have no desire to ignite fuel fume pushing out of the engine, nor getting zapped.
 
To test for spark: if you have an extra (or old) spark plug, simply pull the wire off of one of your plugs, put it on the extra plug. Lay the plug on the engine so the metal base touches the engine, crank the starter. You should see spark. If you don't have an extra plug, just remove one from the engine and follow the steps above. No worries about igniting fuel fumes. Keep your body parts away and you won't get zapped, either.

To test the coils: remove the fuel tank for access to the coils. Each coil has two small wires and two large wires. A few inches (or a few more centimeters) away from the coils, there will be a connector for the two small wires. Take that connector apart, use the ohms section of the meter to measure the resistance of the primary side of the coil. It should read in the 3 to 5 ohm range. To check the secondary side, pull the leads off the spark plugs. Put your meter leads in where the spark plugs go. One coil goes to plugs 1&4, so put your leads in there. You should get a reading of close to 30,000 ohms. If you get a lot more than that, unscrew the caps from the wires, measure the actual wire resistance without the caps. You should get about 20,000 ohms. That will help determine whether you have bad caps or wires. While you have the caps off the wires, trim about 6mm from the end of the wire, then screw the cap back onto the fresh wire.
 
Thanks a lot for your tips. I just finished measuring everything, and was surprised what I found:

[table="width: 500, class: outer_border"]
[tr]
[td]
Item​
[/td]
[td]Primary[/td]
[td]Secondary[/td]
[/tr]
[tr]
[td]
2&3 Coil​
[/td]
[td]4Ω[/td]
[td]15kΩ[/td]
[/tr]
[tr]
[td]
1&4 Coil​
[/td]
[td]6.4Ω[/td]
[td]15kΩ[/td]
[/tr]
[tr]
[td]
Cap #1​
[/td]
[td]4.9kΩ[/td]
[td](5k imprinted)[/td]
[/tr]
[tr]
[td]
Cap #2​
[/td]
[td]8kΩ[/td]
[td](no markings)[/td]
[/tr][tr]
[td]
Cap #3​
[/td]
[td]flaky continuity[/td]
[td](on contact averages 400kΩ)[/td]
[/tr][tr]
[td]
Cap #4​
[/td]
[td]no continuity[/td]
[td]-[/td]
[/tr][/table]

How on earth do the caps go bad? Also, I found out that some PO installed BR7ES instead of the stock B8ES spark plugs - the integrated resistor certainly doesn't help things!

I'm not too sure about the 6.4 ohms coil.
 
Caps go bad due to corrosion of resistor and internal contact. Ignition coil 1 and 4 is weak on primary side. Feed it some 12 volts for a minute or two and see if it will then ohm to about 4 on primary side as it might be an internal corrosion issue.
 
My experience is that what are called 3 Ohm coils should read nominally about 3.8 to 4.2 Ohms resistance and secondary resistance will be right about 16K Ohms. The issue with the plug caps is that someone has mixed resistor and non-resistor components possibly? The power you get at your plugs is the result of how much voltage is powering the coils and resistance. The 6 plus Ohms means resistance has crept up and will weaken the spark.

It is kind of pointless to measure the power to the coils which is what is a factor that is multiplied by the coils since your battery is down. Get a new battery or test yours for sulfation of the cells using a motorcycle hydrometer (they only cost a couple bucks at an autoparts store... look like small eyedroppers). Anyway, if you find that you are getting a considerable amount less at the coils than the battery voltage while resting, search around for "coil re-powering" as it will help take care of the problem OR clean or replace a lot of connectors and switches.
 
Thanks, guys!

After taking apart one of the caps out of curiosity and some research, I ordered new parts. Pity I can't just stroll into a shop around here for these... Since I've got two bikes, I swapped over some still-good-enough caps (they went bad on the second one as well) for the meantime. Not that I expected much, but yeah, no luck.
Judging from the exhaust temp, it's now 'only' #4 which isn't firing. Worth a try though.

I ordered new spark plugs, caps and a battery - unfortunately, your messages reached me during the night (different continent), so a new coil wasn't part of the order (bit pricey here).

I'm tempted to believe that the dead battery pulled the voltage just way too low during one or both of the 1&4 firing cycles, and a new one would smooth the voltage enough for the 1&4 coil to get enough power - so that I can ride again until a new coil arrives. We'll see.

I did measure the resistance directly at the coils itself, not at the connectors. They are in good order, no corrosion or charring at all (Though I plan to rewire her anyway), but as suggested,
I'll connect a 12V supply and measure the voltage arriving at the coils to be sure.

There is no point in troubleshooting the current battery, as I has been through the ordeal of both a failing rectifier and regulator, and doesn't take a charge properly by now.
 
Well. Connected a 12V supply yesterday, but it's too wimpy. Drops down to 6 Volt (measured directly at the supply) as soon as I power up the coils, so I didn't go any further.
 
After replacing the caps, spark plugs and the battery, she runs better than ever. In fact, I got a bit of a scare, as the rear wheel slipped until I adjusted to all this newly available torque! :)
 
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