Need help with inconsistent spark

[Guest]

I noticed my points needed to be replaced, so I just installed a Dyna S (it was on my list of things to do anyway). When I used the timing light, the coil for cylinders 1/4 were very clear, consistent, and I was able to line it up perfectly. When I probed the plug wire for cylinder 3, the spark was erratic and inconsistent. I could sometimes see the 1/4 mark on the rotor show up, then it would take a quick pause from any spark. Same happened with plug wire 2. Went back to 1 or 4 to be sure my friends Harbor Freight timing light was OK, and all was peachy there again. Same was happening with the points when they were installed.

I tested the coils by probing the O/W to the White wire, then again for the other coil and got a consistent 3.9-4.2 (with stock coils and Dyna ignition).

I plan to get new Dyna coils and plugs anyway, so this may be the time. (Green 3 ohm coils and 7mm copper coil wires sounds right?) Do I have to get the NGK plug caps as well?

[tkent02]

Same was happening with the points when they were installed.

This is the key. Swap coils and see if the problem moves with the coil or not. Don't even need to unbolt them, just switch wires.

[azr]

I'm guessing you did a typo..but when you are doing 2-3 make sure you're looking at the 2-3 markings on the rotor.

[Drewbis1]

Regarding the 2/3 markings... I was only using a timing light. The spark was delayed and erratic, so I could MOST of the time see 2/3 on the rotor, but every second or two I'd see 1/4 quickly. And it was a very delayed spark pattern compared to the 1/4 coil. I'd say the 1/4 was making 3 times as many sparks as the 2/3 when held at 2500 rpms.

[OldVet66]

I would recommend the Dyna 8mm suppression wires, and forget the caps. Once you change the coils and things work normally with the timing light you might find you need to slip the 2-3 module a bit on it's set screws to get those marks dead on.

[Drewbis1]

What would be the benefits of the suppression wires over the copper core?

[Chuck78]

If your wires and coils are good (do the swap as mentioned, swap plug wires 1-4 to 2-3 and vice versa, and also swap the wires coming from the points, I forget the color, but not the 12V power source, the switched negative ground from the points to the coils. See if the trouble follows the wire swap. If not, you probably are running too rich on 2 and /or 3 and fouling out the plug(s) a bit, which is causing a delay in the spark finding its way to the ground electrode. could even be as weird as a dirtier air filter but vacuum leaks on carbs 1& 4 to even it out... unlikely but you never know. Don't know the history of the bike, but you really need to dismantle the carbs 100%, soak them in berryman's for a day, replace all the o-rings (install with a little oil to make them slide and not tear) from cycleorings.com, replace the intake boot o-rings to the cyl head, inspect the intake boots really well, rejet the carbs if pods or aftermarket exhaust is being used, bench synch, run bike, vacuum synch after adjusting valves by swapping shims to get the proper clearance and valve opening lift. You;ll probably need a new top cover gasket when you do the valves for the first time.

Suppression wires have the resistance built into the wires and use standard ends. copper wires have almost zero resistance, so you use resistor cap ends like the NGK's that have a 5000 ohm resistor or other sizes in them. The coils are designed to run on some resistance, and I think you may even risk burning them up if you don't have suppression wires OR resistor caps. the resistance eliminates electrical signal interference on the suppression wires. Car radios would be all scrambled if cars used solid copper wires.

[Chuck78]

I'm running a back from the grave pieced together old Dyna S built from two failed units (they don;t like overheated bikes), 7mm solid wires, NGK 5k ohm caps, and some knock-off Dynamite (Dyna Green 3 ohm ) coils. Works beautifully!

[Drewbis1]

I just swapped the coil wires. Disconnected all 4, white now to black, black to white, the swapped the orange/white to the other orange/white. Tried to start it and nothing. The starter motor was going, but didnt start the engine. Then a loud backfire from the exhaust with a badass flame. Swapped back to proper wiring and i dont seem to be getting any spark from cylinder 3 now. Still erratic spark from 2, and 1/4 are still **** on.

I should note that my 12 volt power to the Dyna ignition is spliced into the orange/white for the 1/4 coil only. I dont have a terminal where the 1 O/W coil wire is split into 2 for each individual coil.

[Drewbis1]

Got it sorted. It was a bad connection at the spark plug cap. Removed them all, trimmed a little off the wire and reinstalled. Timing light is good to go on all 4 cylinders.

Still have the Dyna coils and wires arriving on Monday. They will still get installed and all should be good.