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XR75 Ignition woes...do I need a new coil??

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Hey guys, been struggling with no spark on my 1975 XR75 project. I have some pretty high voltage but just not enough to jump the gap on the spark plug.

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I am getting about 85 volts from the spark plug lead on my (cheap) multimeter, and spikes up to the 460 volt range on my voltage tester. I'm also getting a healthy shock if I touch the lead. I think the yellow meter is more accurate here, because of the "spiking" nature of the voltage.

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I replaced the points and condenser. The spark plug checks out ok on another engine. All wiring is sound and I bypassed the plug boot.

I hate to spend $60.00 on a new secondary coil (especially if it's not the problem) but I'm out of options. Everything seems to be functioning, but just not quite enough juice at the end of the line. I did the resistance and continuity tests on the coil from the repair manual and everything seems ok, but the book says Honda doesn't provide specs for this particular bike. The stator lights up a non-powered test light (blinks) nicely, but I'm finding it hard to measure the stator output with the multimeter.

Any ideas before I order a coil?

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that's a whole bunch of good looking shiny paint on that thing are you sure things are getting grounded as they should through all that paint ? Just askin'

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Actually it's powdercoated...but yes, I ran a ground wire directly an exhaust stud just to be sure (for testing). I know the ground b/w the frame and coil bracket is good too, because I had to run a tap through the holes after powdercoating.

What's especially annoying is that it had good spark before the resto., but obviously that doesn't mean a part like the coil couldn't have gone bad between then and now.

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I'm with bruceD on this one... You even said "it had good spark before restore".So what has changed?

Make sure the coil and motor mounts are cleaned first.Don't trust a non grounded frame system.

Also,What gap is on the points? What ohm is at the exciter coil.?

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I have a XR like that one and one time when I pulled the flywheel the advancer pulled off and when I put it back on I was 180* off with it so the points were opening at the wrong time and out of faze and had a weak spark at the wrong time so it wouldn't run,you might look there.

Ed

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Thanks for the input. I will check the resistance on the stator coil and report back. I'm pretty sure my repair manual doesn't have specs for the stator coil resistance. I know there's continuity in the stator coils. I was really hoping the stator isn't bad though. I've never seen NOS or aftermarket stator coils and everything I've seen or eBay looks way worse than mine.

I'll also check the points gap again. As I'm sure you know, the adjustment mechanism is somewhat crude, to say the least, on these bikes, and a real PITA when the flywheel is in place.

As far as the grounds are concerned, not sure what else I can do...the stator plate screws right in to the block and I am using heavy gauge wire to an exhaust stud to test for spark at spark plug lead. I did consider grounding issues from the start due to the powdercoating.

As far as what changed, I actually had no intention of messing with the ignition system before I ran into this problem...so it's been driving me nuts too. I suppose just moving 36 year-old electrical parts around, and getting them wet, could've pushed something over the edge.

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I have a XR like that one and one time when I pulled the flywheel the advancer pulled off and when I put it back on I was 180* off with it so the points were opening at the wrong time and out of faze and had a weak spark at the wrong time so it wouldn't run,you might look there.

Ed

Thanks, I didn't remove the advancer; just cleaned it up in the parts washer. Keep the ideas coming though!

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It's FIXED!! It was the points gap...Way too wide, they weren't even closing all the way. I had to cut up my feeler gauge to set them but it was well worth it. Thanks SJ!

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