Random No Spark

[Nilson]

Ok update.
We started cleaning/checking connection etc... Cleaned one of the main connector plugs under the harness and it fired right up. Ran great with no problems for 3-4 days then on my first long ride bam right back to the same problem of no spark. Went back to checking grounds etc... cleaned up around the signal generator, removed some grime/corrosion and it is up and we are up and running again. Been starting and running every time for the last two weeks, but I am still leery of a long ride at this point so keeping it close to the house for the next hundred miles or so. Fingers crossed.

[tom203]

Rather than crossing fingers, use them to clean Connections. While you're messing around, do the quick test in this link to evaluate your charging system. This is a real common problem,so find out before it finds you!

http://www.thegsresources.com/_forum/showthread.php?164993-Charging-System-QUICK-TEST/page2&p=1272192#post1272192

[Nilson]

Grrrr...Back to the drawing board.

It is losing spark again. This time it is not for long 5-10 mins of sitting and then it is back.
I just don't understanding this intermittent stuff....It seems like it if fixed then nope.
This bike might be headed for craigslist.

[tom203]

Here's an old idea- check your charging system! Just maybe it's doing something odd and the ignitor is upset. If it turns out it is your ignitor, you can get a dyna ignition system for about $120 depending on where you are.
Hey just where are you?
Craigslist has plenty of these things already.

[Brendan W]

My starting point would be to check the voltage arriving at the coil itself, not the plug. If it's more than 0.5 Volt below battery voltage you may have a connection and or switch problem. The usual suspects are the ign and kill switches which corrode over time but are easily opened and cleaned. Unfortunately cleaning connections does not deal with the frequent problem of corrosion of the wires at the back of the plug pins, particularly the plug for the coil itself and generally the design won't let you see the condition unless you break it open. I have found a few bad spots by getting the bike running and then vigorously wiggling the plugs for the coils,ignitor,ignition switch etc trying to force the issue.
It's far more likely that this kind of thing is causing the problem and certainly worth exhausting as a possibility before going off on a replacement lottery with coil, ignition boxes and the like.

[greg78gs750]

i liked the right hand switch short idea. go over all the wiring with a fine toothed comb, it costs nothing but time and will eliminate some possibilities.

[timbrigham]

I bought this bike from the previous owner... i had some background on old car electrical systems.

Turns out there were a couple volts getting though to the spark plugs but not near enough to fire.

I started from the battery and found one of the ignition coils totally shot (no ohm reading from the boot, and geting crazy hot). The other was loose.

Could this have been the underlying problem, or just a symptom? Also I'm a bit leery about replacing with another used trandformer coil... how should I pick an appropriate aftermarket model? The primary coil comes back at 4 ohms.

[tom203]

I bought this bike from the previous owner... .....he primary coil comes back at 4 ohms.

help us out here, what bike model year etc.? And welcome.

[timbrigham]

It's the same 81 GS450L as the original poster of this thread. He asked me to let him know what I found... figured posting here he'd have the chance to see it.

When I unplugged the problematic coil it immediately sounded better trying to turn over. That's why I'm wondering if that may have been the cause of this behavior.

[tom203]

"......It's the same 81 GS450L as the original poster of this thread."
So you are the PO? Yes, a shorted out ignition coil would change cranking noise/behavior, but the random problem he's describing can be challenging to find. Connections need to be inspected/cleaned before you can be sure it's the ignitor itself. Or you can uses jumper wire to bypass stuff (see earlier reply) and determine ignitor's condition at the moment this problem occurs.

[eil]

It sounds to me like timbrigham bought this bike from Nilson. Correct?

If so, welcome and don't miss the link to the mega-welcome in my signature. It's tempting to fix the most outstanding issue to get the bike running and then call it good but chances are there's a lot more maintenance that bike needs in order to be safe and reliable.

OEM coils can go bad, but rarely do. If you decide you need a new one, a used one should be fine, especially if you buy from a member here on the forum. However, it's more likely the spark plug caps are just in bad shape. You can either buy new ones (NGK makes good and cheap replacements) or see if the old ones can be serviced. They can be taken apart and rebuilt pretty easily if the rubber is still good.