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