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Discussion Starter · #1 ·
Had an odd problem with my '87 sportster today. Fired right up this morning and ran fine through town. Got on the highway and the higher revs, and after maybe 5 minutes, it abruptly started misfiring badly, backfiring, bucking and running like ass. The tach still indicated RPM, so the bike didn't lose power (these HDs use thermal breakers instead of fuses- when the ignition ones "breaks", the tach goes right to zero).

After about 10 seconds it suddenly started running fine again. Another minute, same thing, bucking, backfiring, no power at all. After it had been doing this for 10-20 seconds, the circuit breaker tripped and the lights (and tach) shut off. Coasted to the side of the road. There was no power to anything. No lights, no dash, no starter. Checked the battery connections and ground to the engine, fine. Checked the key switch, fine. Normally the breakers reset on their own after about 5 seconds. The main breaker was not resetting. I jumped the terminals with my leatherman, got a massive arc, and the power came back on. Hit the starter and it spun over strong, but not so much as a pop of ignition.

I pulled the points cover off, and cranked the engine to watch the gap. There wasn't one. The adjustment plate must have vibrated itself loose, and scooted over, eliminating the gap. I eyeballed the gap and re-set it. Hit the starter and it fired right up. Got it back up to speed and within about a minute, the breaker tripped and shut the bike off for about 5 seconds, it reset and everything came back still running fine. At this point I turned around and headed for home, dealing with about 10 seconds on/ 5 seconds off until I got off the highway.

In town, it quit shutting off, but then started to not run that great again. Not as bad as before, but some misfiring, popping, ect. Managed to limp it home.

My understanding was that this bike had a breakerless ignition from the factory, but was converted back to points due to reliability. It also has a screamin eagle ignition box that's hooked up to factory connectors- I've never seen an ignition box on a points ignition, but it won't start if you unplug it.

Anyway, I can gather that as the point gap was closing, it was arcing and causing the misfires, and when they closed entirely, it was feeding power to the coil constantly which drew too much power and tripped the breaker. Could this have fried the condenser, or is there any way to test it? I set the points gap properly and it mostly runs OK now but doesn't like to run at high rpm for more than a second or two before it starts missing and popping.

One other little thing- since I got it the tach works fine, up to about 4000rpm. Past that, it starts wavering and swaying around, moreso with more RPM. I though it was a bad tach, but I tried another known good one and it did the same thing. Nobody on Harley forums has a clue about why that might be.
 

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All the condenser is supposed to do is absorb excess energy to prevent arcing at the points gap to help them last longer/less pitting. I've seen some engines (autos) run perfectly fine without any condensers at all, but the points will die fast. I've also seen condensers go bad and do exactly what you're describing.

As far as your CDI box, you could remove it,but it's not as simple as just unplugging. All ignitions have breakers. "Electronic'' ignitions typically use magnetic breakers. Yours, being points, just so happen to be mechanical. No disadvantage at all as long as your point spring is healthy (point bounce/ spark flutter at speed) and the feet are healthy. But you will have rubbing block wear that will affect your dwell. Your points are just pulsing the CDI (which is basically just a bog, extra capacity coil). Is the rubbing block OK? I've seen those get old and break up.

It's rare for something mechanical ,like points, to ''die'' instantly. If your points feet, rubbing block,dwell and gap are all good then I'd suspect the condensors. Thats a quick,cheap test anyway. It's possible the CDI is dying. You could wire around the CDI so your points are pulsing your coils and see if eliminating the CDI is the culprit.

Also, a stuck shut set of points could seriously overheat a coil. Got any extra coils laying around you can toss on?

No clue about the fuse thing,though. That's just weird.
 

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Shiny you deserve a 5 for that cause I was just about to make a smart ass remark about "points", then I read your post.

Razed, sounds like multiple problems. Probably the points being closed is un related and just part of the whole irritating points game. (I have no idea why people think they are more reliable).

I would try the condenser but it really sounds like a coil/ bad ground vibration thing to me.

Funny that you have a cdi and points... for reliability...




Good luck, keep us posted.


Jon


PS, I used to keep 3 sets of spare points in my VW, you never know.:nuts:
 

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Discussion Starter · #4 ·
The points look fairly new and are not OEM, and the rubbing surface looks OK as well. Contacts look like new.

The wire from the points goes directly to the + post of the ignition coil, along with two others- one is the tach signal, the other goes to to one of the ignition box's 5 pins.

The weird floating tach at high rpm makes me suspect some degree of points float/bounce, though it runs strong all the way to redline. I did notice the little cam that pushes the points has a bit of play in it. Have to dive into it further. Probably test the coil to see if that might have been cooked when the points were stuck shut.
 

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Discussion Starter · #6 ·
Pulled the whole ignition "cup" out of the engine. Behind the cam is a mechanical advance setup- two flyweights sprung together with tits that protrude into notches in the cam, so as the weights fling out with RPM, it rotates the cam an additional 10* or so. Not really any way to get rid of the bit of slop and nothing seemed excessively worn so I guess that's just the way it is.

Tested the coil and the ohms were in spec. Set the points gap correctly and put the timing plate in a conservative angle for minimum advance. Took it for a short ride and everything seemed fine, though the engine didn't feel as "hot" as it used to, I'm sure from less advance. Although reading into the 1250 kit, it's widely suggested to run less advance than a stock motor and a flatter advance curve- retarding the adjustment plate and tightening up the springs on the flyweights. Might have to scrounge up a timing light and play around with it a little more and start cranking up the advance again.

Guess the coil may have overheated and started acting up when the points were stuck, and it briefly sitting on the side of the road wasn't long enough for it to cool off.
 
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