scumbag51 Posted March 3, 2008 Share Posted March 3, 2008 I have a 1982 Yamaha Maxim XS400J, project bike. PO says it had sat outside uncovered for a year, and it looks it. No ignition key, so I hot wired the ignition switch. Installed new battery. Voltmeter shows current getting to all the places it should be when the ignition switch is "ON", but there is no spark. Water must have gotten inside the right handlebar switch cluster. Brake light, kill button and start button are all nonfunctional. I hot wired the kill button, and hooked up a temporary start button to work the starter solenoid. The engine cranks over fine, but no spark. I've traced every circuit in the ignition system right down to the spark plugs. This is what has me stumped. Current flows from the CDI unit to the coils, then to the plugs. It's my understanding of the way that the coils work is that current flows through the primary circuit, until it is interrupted by the CDI unit (breaker points in the old days), then a charge is induced into the secondary circuit, which then sends a pulse to the spark plug to fire that cylinder. Checking the leads from the CDI unit, I see that there is current coming from both leads at the same time, though weaker on one of them. I would've thought that the current would come from one of the leads, through the coil, and returned then to the CDI unit. Also, although there wasn't any visible spark, I put the test lead on the tip of the sparkplug to see if there was any current getting there at all when it was supposed to fire. I was surprised to see that there is constantly a current flow at the tip of the plug. This makes no sense. How is the plug going to fire when there is always a current there, unless we're talking about a diesel engine, which we're not. I think I would attribute this to faulty coils, but the current coming in both directions from the CDI unit is what makes me think there may be more to the problem than the coils. Well, that's where I'm at with my project bike. Rather than to just start replacing rather expensive electrical components until I accidentally find the right one, I thought I'd ask for help on this forum. Any opinions anyone would like to offer would be greatly appreciated. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted March 3, 2008 Moderator Share Posted March 3, 2008 I have a 1982 Yamaha Maxim XS400J, project bike. PO says it had sat outside uncovered for a year, and it looks it. No ignition key, so I hot wired the ignition switch. Installed new battery. Voltmeter shows current getting to all the places it should be when the ignition switch is "ON", but there is no spark. Water must have gotten inside the right handlebar switch cluster. Brake light, kill button and start button are all nonfunctional. I hot wired the kill button, and hooked up a temporary start button to work the starter solenoid. The engine cranks over fine, but no spark. I've traced every circuit in the ignition system right down to the spark plugs. This is what has me stumped. Current flows from the CDI unit to the coils, then to the plugs. It's my understanding of the way that the coils work is that current flows through the primary circuit, until it is interrupted by the CDI unit (breaker points in the old days), then a charge is induced into the secondary circuit, which then sends a pulse to the spark plug to fire that cylinder. Checking the leads from the CDI unit, I see that there is current coming from both leads at the same time, though weaker on one of them. I would've thought that the current would come from one of the leads, through the coil, and returned then to the CDI unit. Also, although there wasn't any visible spark, I put the test lead on the tip of the sparkplug to see if there was any current getting there at all when it was supposed to fire. I was surprised to see that there is constantly a current flow at the tip of the plug. This makes no sense. How is the plug going to fire when there is always a current there, unless we're talking about a diesel engine, which we're not. I think I would attribute this to faulty coils, but the current coming in both directions from the CDI unit is what makes me think there may be more to the problem than the coils. Well, that's where I'm at with my project bike. Rather than to just start replacing rather expensive electrical components until I accidentally find the right one, I thought I'd ask for help on this forum. Any opinions anyone would like to offer would be greatly appreciated. ignition works by providing 12v to primary and an earth, contacts/cdi then interupts the earth but the current now has nowhere to go except to secondary and then jump the gap of the spark plug as this is the easiest path. maybe you can interupt the earth to create a spark at the plug. ( not too long as the coil heats up) i would suspect either a faulty earth on the cdi or the cdi itself. Link to comment Share on other sites More sharing options...
scumbag51 Posted March 8, 2008 Author Share Posted March 8, 2008 ignition works by providing 12v to primary and an earth, contacts/cdi then interupts the earth but the current now has nowhere to go except to secondary and then jump the gap of the spark plug as this is the easiest path. maybe you can interupt the earth to create a spark at the plug. ( not too long as the coil heats up) i would suspect either a faulty earth on the cdi or the cdi itself. I found that the reg/rect and CDI unit both go to a common ground which was bad. Don't know yet if that will solve the problem, but you were definitely right about that. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted March 8, 2008 Moderator Share Posted March 8, 2008 I found that the reg/rect and CDI unit both go to a common ground which was bad. Don't know yet if that will solve the problem, but you were definitely right about that. not just a pretty face yer know!!! seriously, let us all know how you get on for the benefit of present and future posters! Link to comment Share on other sites More sharing options...
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