Ignition Circuits

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Ignition Circuits

Postby EKHKHK56 » Fri Jan 15, 2016 2:18 am

I want to extend this to you folks in case it is ever needed. If you have a no spark situation on any vehicle here are some tips to troubleshoot. Use a 12volt test light. Key `ON` Go to the coil and check for power at the positive side. This comes from the ignition switch but may go through an oil pressure interrupter circuit on some equipment or vehicles. So check for power on the positive side. Than while cranking, check for constant power at the positive side and on off on intermittent power at the ground side. Hot Ground Hot. If you have this situation and no spark your coil or wires are bad. Check coming out of the coil center with a jumper wire held 1/4" from ground. If spark there, bad coil wire. If no spark bad coil. If spark out of coil wire but not plug wire at spark plug than rotor burnt through to ground or bad plug wire. If you have no voltage to the positive side of coil with key on you have a bad circuit, ignition switch or an interrupter. Bad circuit is often a fusible link feed burned or such. If you have power at positive side of coil with key on but not when cranking than you have a bad ignition circuit in crank mode. This feed engages with the starter circuit either from the ignition switch or starter solenoid. It should be a full 12 volts during crank and than for point ignition the feed should drop to 9 volts or so through a resistor in run circuit. This keeps points from frying. If you find no Hot Ground Hot at the negative side of coil that`s a problem. If the circuit just reads ground only the points wire could be grounded, the points may be defective and grounding or not opening due to cam broken or worn out. If it reads hot only than the points are not closing. Electronic ignitions are the same but fancier. Make sure you have constant power in `on` and `crank` mode at positive side of coil Than check the ground side, it should flash on off on while cranking, checking with a test light. If it stays on steady or off steady that's a problem. In the distributor or at a crank sensor is the device that signals the module to fire the coil. Just like points the module grounds the negative side of the coil causing the voltage to reverse and coil to spark. The module needs the signal from the distributor or crank sensor to time the sparks and create them. If no on off on action at the negative side of the coil during cranking disconnect the distributor pick up coil or crank sensor and test it for a small A/C self created voltage during cranking. If none present it is bad. If it is making A/C volts than the module is bad. All this assuming you have good connections on all feeds and grounds. Now anyone can look for that missing spark in the parking lot! Erik K
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Re: Ignition Circuits

Postby sportsterpaul » Fri Jan 15, 2016 2:54 pm

I like this much better than "Have your girlfriend hold the plug while you kick, if she jumps, you have spark." I would add the most common problem I have had is condensers. They are filled with electrolyte and will dry out and stop working. Now that they are all aftermarket quality is generally shoddy. Don't be surprised if the brand new condenser stops working or doesn't work at all. Not starting is one failure mode, but I also had a bad condenser that let the bike start, but it could not rev above idle, and would burp and backfire.

Points are pretty reliable, you can just pry them open and look at the contacts. I have only worn one set out in my life, and that was the rubbing block, not the contacts themselves. It is amazing how raspy the contacts can look.

If you leave the ignition on, like the bike stalls as you park it and you forget to turn off the ignition, you will drain the battery sure, but I have also had the coil overheat and split. This is the new plastic type used in the 1970s.

On "cone" motors, the most common failure is the fly-weights egg out and start beating against the back side of the breaker plate. Then the center screw snaps off at the camshaft. Real joy. Happened once to me, at Immigrant Gap, half way between San Jose and Reno. I carry an entire spare mechanical ignition set, even on bikes with electronic ignition. I use anti-seize on the 1/4-24 screw and if you are really lucky, you can walk the broken piece out of the camshaft with a scratch awl.

A big thing is visual inspection. I don't even put the cover plate on the cone motor ignition. I get caught in the rain and the points don't seem to care. For electronic ignition that you put in the cone, I think it is essential to leave the cover plate off so the electronics stays as cool as possible.

The "stand-up" circuit breakers in pre-cone motors are very little trouble. The just seem to work.

If its night you can turn on the headlight and slowly kick to see the points open close. As the load changes there may be a very small change in brightness. Much better to use Erik's method.

I can't help much with magneto bikes-- if they work they work and stay working, there is a reason they use mags in airplanes. My first suspicion is plugs-- make sure the small gap is clear, heck carry a couple spares that are gapped and ready to slap in. After that, I would suspect condenser, if the points look OK, and open and close as you kick the bike over. I did have a carbon track form inside one cap, and a new cap fixed that.

I always wanted to slap a mag into a cone motor gearcase, they make special mags that drive off the tach drive hole. Then I would still run the cone, and have dual-plug heads. Completely redundant ignition, that would be great, like two mags in an airplane.
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