Help Me Test Simple Motorcycle Ignition System

[Jandrews]

Originally Posted by john70t

Start with what has changed while stored: Battery, gas, possible rust/condensation.

Battery first.
Easy to test these things: Should maintain ~9.5V while cranking under load(9V min). ~12.6V after a rest. ~13-14V after charging.

Good advice, john70t.

I completely drained and flushed the tank and petcock when I went through the carb. I also installed a brand new fuel hose from tank to carb, along with fresh gas. Float bowl gets fuel easily, and I see fuel squirting from the injector jet in the carb when the throttle is twisted.

I did add Sta-bil to this "fresh fuel" at the beginning of the winter, and I have suspected that. But I also added it to my 911, and have had no problems there. I guess before I start tearing into the ignition system it would make sense to drain the fuel again and start with fresh, "unstabilized" fuel.

And yes, I am contemplating getting a new battery too, but I am confounded by the fact that the engine spins strongly during cranking, but doesn't seem to fire. I will perform the "dynamic" voltage tests you indicate below. That may shed some light on the situation.

JA

[hardflex]

Well, if there is an ignition module, it probably takes the place of the condensor.

Bottom line, if there's voltage to the points when they're closed, then you break the points, you should get spark at the plug.

[Don Ro]

Speaking of battery health, I have always wanted a load tester - bought one last week.
Good luck.
.
Schumacher BT-100 100 amp Battery Load Tester : Amazon.com : Automotive

[ltusler]

The engine spins strongly, maybe its not getting enough compression, stuck valve or ring(s)?

[Jandrews]

Ok...battery is toast. Just checked it after a week on the trickle charger (indicator showed fully charged) with no prior starting attempts. VDC was 13.1. Tried to crank it with the compression releases pressed and it cranked slowly and VDC dropped to 9, then 7, then 4, and it then only clicked. Resting VDC was then 11.5.

Clearly I need a new battery, and I will get one. I guess we will see what the new battery does, but shouldn't a jump start essentially mimic a new battery? I am concerned that I actually killed this battery while trying to get it to start over the past month or so. I can get it to crank fine with a battery charger/starter, or with jumper cables, but it will not start. I would hear the occasional fire during fast cranking, but the engine would not start. I have not tried jumper cables or the battery starter/charger today.

I want to be careful to not destroy the new battery as well. I guess if it doesn't start right away with the new battery, I should set it aside and then go after the ignition. I need a new battery anyway, so no harm there.

JA

[Nostril Cheese]

Check connections. Like I said, I'll bet something rattled loose.

[Jandrews]

Thanks Nostril. I have checked, cleaned and snugged all connections from the battery all the way through the spark plug wires.

JA

[johnco]

check resistance of plug wires and coil. also ground to coil

[Jandrews]

Thanks johnco.

I will check plug wire resistance now. What value should I be looking for? And how do I check coil resistance? And what value and I looking for there?

JA

[johnco]

can't locate my old harley workshop manual right now but you can probably find the specs online. found this online

Check primary resistance by connecting your ohmmeter between the screw posts that the wires connect to. Stock coil is between 2.5 to 3.1 ohms.

Check secondary resistance by connecting your ohmmeter between the spark plug towers. Stock coil is between 10,000 and 12,500 ohms.
andThe primary coil (the two small prongs) should be 2.5-3.1 ohms. Mine is 3.4 and works fine (except when the bike randomly shuts off). The secondary coil (between spark plug cables) should be 10-12.5k. I think mine was 11ish. If yours is only 1k ohms, it means your coil is shorted and needs to be replaced. Just make sure your tester is set to the right values as well.

and



Set the ohmmeter to read resistance on the "Rx1" setting. Measure the resistance across the two smaller terminals on the coil. The meter should read between 2.5 and 3.1 ohms.

4


Set the ohmmeter to read resistance on the "Rx1000" setting. Measure the resistance across the two larger terminals on the coil. The ohmmeter should read between 10,000 and 12,500 ohms.

5


If the meter reads outside of the ranges for either of the above measurements, then the coil is faulty and should be replaced.

[johnco]

found this also
The manual says they should be around 4K and 8K

and this

Harleys plug wire resistance spec is 250~582 ohms per inch

[johnco]

those values may or not be correct for your particular bike but they should give you some idea of their condition

[johnco]

not sure if this engine is electronic ignition or points, but the points and condenser would be located on the right side behind that round cover with the maltese cross. easy to check if they are burnt or corroded. slide an emory board between them and clean them up a bit and try again. it's been a long long time but I believe my first harley used 6 cyl chevy points

[john70t]

I think there's a way to test if the ignition primary side is trying to charge up the coil.
This indicates the points/IM with everything on the chain is working, but be aware it still may not be tuned or timed.

You put a voltmeter on the 12+ side of coil and ground, and check if there is switching on/off.

[johnco]

could be something simple as a loose coil. my engine kept cutting out, misfiring and finally died ontop of a bridge one day and wouldn't start. found my coil bolts were loose and coil not getting good ground. had to drive 10 miles home holding coil tight to frame.

[Jandrews]

Thanks johnco and john70T. It will be several days before I get a chance to do some of the checks you recommended, but I will do them and report back.

Thanks,

JA

[john70t]

Take it easy on that little tiny starter motor. 5-10 seconds max. It either fires or it doesn't.
Smelly tailpipe means it's flooded, ain't gonna fire without nuclear plugs, and needs a rest.

Nice ride btw.

[Don Ro]

Originally Posted by Jandrews

Thanks johnco and john70T. It will be several days before I get a chance to do some of the checks you recommended, but I will do them and report back.

Thanks,

JA

Yes, report back...'got me interested now.