Topic: Weak spark...how do I tell?

[mossen]

My 550 wouldn't start today. Wouldn't even fire. Grounded my spark plugs against the engine block today to view the spark. In my manual, it describes a fat blue spark that I should see, but I didn't see anything fat, it was just these little wimpy sparkles...I don't know how to describe it...like fairy dust or something. It was pretty small. The bike ran a few days ago, although I don't have anything to compare it to because I'm new to moto and I've had it for only a short time, so I have no idea if it was running "good" or not. Is there a test to see if my spark is proper?

Thanks
mossen

[bender01]

Did the battery work or were you kicking it over? The battery needs to be strong, but you saw spark?! Do you have enough gas in the tank? On reserve? Kill switch on?  Fuses? Has to be simple if it ran a few days ago. What year 550? K or F? 

[ChortlingSandcaster]

Hi, what year is your 550 four?

How old is the battery?  Did it sit idle over the winter?
Can you trickle-charge and re-test?

If it was running one day and not the next, as you said "The bike ran a few days ago"
and now it is not -- a marginal battery could very well over 'a few days ago' cross
the threshold to being 'just sufficient enough' to not sufficient.

Do you have a battery trickle charger?  If not, you can buy one for cheap at your
local auto parts store. 

Do you have electronic ignition?
Or is it stock points and condensor?

[Hush]

Spark should be quite discernible, fat/blue is a nice look.
Have you got any known good plugs?
Don't have to be for your bike as they are not going to be put into it, use these same as you did before and see if there is a noticable difference.
Your points may need a clean-up too, clean them with either a very fine points file or a non waxed business card, that may make all the difference to your spark delivery.

[mossen]

It is a stock 1978 550k. The plugs are D7EA. Battery is new last fall and I had it on a charger every week or so over the winter in the house. It sure spins the starter nice and quick. Just set the points last fall too, didn't notice any concerning wear. There is gas in the float bowls.

Today I took the headlight apart because I had to do some work on the wiring, and I suppose I could have inadvertently loosened some connection. But I still had spark, and it looked about the same as when I checked it last week, so I don't think I broke something. I was just wondering if maybe there is some sort of electrical test I could do on the coils, or some other part that could maybe help diagnose why my spark is not a fat blue arc. Its more of a thin whitish/blue sparklet.

The bike seems to run well, when it runs. Its never completely been dead like this before. It idles more or less smoothly and accelerates OK, although sometimes there is a noticeable misfire...

mossen

[Spanner 1]

Your points will tarnish when the bike is not used. Even if they 'look' clean they can be non-conductive. Shine 'em up and try again...
In other words.. Hush +1.

[HondaMan]

It is a stock 1978 550k. The plugs are D7EA. Battery is new last fall and I had it on a charger every week or so over the winter in the house. It sure spins the starter nice and quick. Just set the points last fall too, didn't notice any concerning wear. There is gas in the float bowls.

Today I took the headlight apart because I had to do some work on the wiring, and I suppose I could have inadvertently loosened some connection. But I still had spark, and it looked about the same as when I checked it last week, so I don't think I broke something. I was just wondering if maybe there is some sort of electrical test I could do on the coils, or some other part that could maybe help diagnose why my spark is not a fat blue arc. Its more of a thin whitish/blue sparklet.

The bike seems to run well, when it runs. Its never completely been dead like this before. It idles more or less smoothly and accelerates OK, although sometimes there is a noticeable misfire...

mossen

The first three things:
1. If the plugs are dark with carbon (on their center tips), get new ones and try again.
2. If the plugs are good and spark still weak, check the points like Hush said. Old condensors can also become leaky and cause this problem: a test is to disconnect them (just remove the mounting screw and lift the condensor away from the baseplate) and open and close the points manually (use gloves!) to see if the spark improves. If so, get new condensors.
3. Plug caps. They can come loose on the coil wires, or be too high in resistance, just from age. This reduces the spark. If you wish to replace them, most bike shops carry new ones for about $5 each: get the 5000 ohm ("5K") variety, in the proper shapes.

[scottly]

Starter spins well, so not a battery/charge problem. What do the plugs look like? Black? Fairy dust sparks around the center electrode? If so, you're plugs are fouled. My best guess is that you made the newbie mistake of running the bike with the choke on. I've never made that mistake, well once maybe, uh twice, then again there was that time.....