Help Me Test Simple Motorcycle Ignition System
 

I have a custom built motorcycle that sits a lot. Recently, it wouldn't start, so I immediately suspected that bad fuel had turned to varnish in the carb. I took apart and cleaned every single piece of the carb, several times, and still no start.

I then pulled a plug, and held it to ground while cranking. Seems like there is either no spark at all, or very, very weak. I tried the other plug (V-Twin), and it sparked very, very weak.

So, I am assuming it is either a bad coil or bad ignition module at this point. I would like to methodically test the system in a way that makes sense for tracing spark. The lifecycle of the spark goes battery, key switch, ignition module, coil, points, plug wires, and then plug. Is that right? If so, how can I go about testing the system end-to-end? Or will the fact that it might be sparking (however weak), make it difficult to find fault?

I can take pics if it would help someone provide assistance. No offense to motorcycle forums, but the guys there don't have the same communication skills as the guys here. I was reading one post where a guy was describing a testing procedure, and it went something like, "u gotta play telephone lineman to see who died at what pole. Put a wire on the + coil and put another wire on the battery and touch it to ground". What????

Anyway, I figured one of the guru's here would be able help me walk through step by step.

Thanks in advance (no pun intended)!!

JA

might help if we knew what kind of engine it is. Harley?

Sorry. Good point.

It is a completely custom build. The motor is an Ultima El Bruto 113" V-Twin (Evo style).

Let me know if that helps any. I can take pics, also.

JA

Here is a basic pic of the engine:

http://forums.pelicanparts.com/uploa...1360470645.jpg

A weak looking spark can be a bit subjective. I'd spray some easy start down the spark plug hole and some in the air cleaner and see if that makes it go - good luck.

And pics of the whole bike please ;)

And the drive side:

http://forums.pelicanparts.com/uploa...1360470848.jpg

Thanks Bill. I can see fuel squirting out of the injector jet in the S&S carb. Plus, I tried starting fluid and nothing.

Here is the whole bike:

http://forums.pelicanparts.com/uploa...1360471060.jpg

Bet you something rattled loose.

Whooo, nice.

Silly question but, how do you know the battery's good?

If the starter will turn that thing over, the battery's gotta be pretty good.

When I was a school boy and my old triumph wouldn't start I used to get my two sisters to push start me down the road. After 25 yards a few puffs of smoke off it went. Good thing about a push start is ALL the battery's power goes into the spark.

I would pull both spark plugs, connect them to the leads (make sure they're grounded, run jumper wires to ground if needed) and then crank it and see what the spark looks like.
That way the battery won't be working against compression.
Jim

A good question on the battery, Noah. It is a Deka ETX20L with 310 CCA. I keep it on a trickle charger, and the motor has compression releases. With a full charge, it will crank the motor over at a good speed. Given the starting problems, I have run it down pretty quickly, but the starter usually gets hot first. Once the starter cools off, I have connected it to an engine starter and jumper cables, and again get good cranking speeds.

Now, it does beg the question that Bill brings up. Is it possible that the battery is strong enough to turn the motor over (with compression released), but not strong enough to also supply a good spark? I assumed not, as my line of thinking was with what Gogar suggested.

And on2wheels, that is exactly what I did. I held the spark plug body to the cylinder, which is when I indicated that I saw little-to-no spark. I even have one of those cool little fittings that snaps in between the plug and the wire and has a light bulb in between. Seems like I could see nothing on one cylinder, and a very, very faint light on the other.

JA

But bench-testing(plugs/coils/starters/etc) doesn't equal working correct under load.

If lack of fuel problem, starter fluid will give one or two strong rotations then die.

I'd try again with a full charged new battery.
I suspect the plugs/gap. It is a custom engine, so sorry no help with that. Check the gaps. The one that is sparking is closer to correct.

Some basic info on coils here How to Make Sparks

wrong or bad condensor?

This bike has run flawlessly for years. This is the first time that it wouldn't start (it typically starts on about a half a crank). There have been no changes (carb adjustments, points, timing, plug gaps, etc...). This is a very low mileage engine (can't ride it for more than a few hours at a time without numbness setting in, LOL!).

I agree with your comments on bench-testing. That is I guess what I was trying to confirm by posting here. I.e. that there is essentially no way to fully load test the components of the ignition system.

If that is the case, I will have to just start replacing stuff and see what happens. Points, then ignition module, then coil.

But, it might make sense to get a fresh, new battery while I am at it. But that is a $100 guess that I was hoping to avoid.

JA

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.

I'm not familiar with that ignition system So just a shot here...is it possible that a faulty ground or a bare wire somewhere is draining juice before it hits the plugs.

Hmmmm....condensor. I had not thought of that. Couldn't be "wrong" condensor, as it has been fine for years. I wonder if the condensor is some how incorporated into the points on this motor? Not sure where to even locate condensor.

JA

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

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.

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

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

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

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

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

JA

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

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

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.

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

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

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

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.

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.

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

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.

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