Comparing ignition coil types

[neilsc]

Would anyone have experience of retrofitting COP coils (stick coils) in place of old style coils with HT leads?

It’s a motorcycle application, the bike in question has a V4 engine and the firing order dictates one coil per cylinder (many older bikes use a wasted spark set-up).

The standard coils have 3-ohm primary and 15k ohm secondary, the HT leads are copper-cored and the plug caps have 5k-ohm suppressor resistors built in. These caps fail frequently because the internal contact between the resistor and a steel spring builds resistance over time. And they’re v. expensive from Honda. Hence the desire to try these COP coils.

I’m looking to fit COP coils from a more recent bike, the primary resistance on these more compact coils measure 1.5 ohms and the secondary 11k ohms.

The current draw on one of the standard coils at idle; - .018 amps (DVM set to DC amps) 0.6 amps (DVM set to A.C. amps). No access to a scope at the moment I’m afraid.

I’m not sure if a series resistor of 1.5 ohms with sufficient wattage rating will limit the primary current enough and if the COP coils inductance characteristics will be different enough to damage the primary switching transistors?

Would anyone also like to shed light on a curious phenomenon I’ve encounter with these failing plug caps?

When the contact between the resistor fails, they often read in M ohm range and I get a misfire. However, if I pull the cap away from the plug by, say, 20mm a spark jumps the gap and the cylinder fires. Why?

Great forum by the way.

 

[evelrod]

An old trick my dad taught me about 60 years ago...
Gapping the plug wire/sparkplug a few millimeters will often temporarily cure a "fouled plug". It simply maxes the available voltage in the ign system. The increase will "cure" the fouled plug if it's not too badly fouled or "bridged".

Pulling the wire off the plug of a running engine, especially a new engine with a capacitive discharge ign, can and WILL be quite a "shocker"...Pardon the pun. ;o) The shock from the 18kv of a "flathead Ford" is not quite the same as that from the ~45kv of a modern system, eh? BTDT !!!!

Rod

 

[clark26]

I work on Car/trucks so I'm not a 100% sure what kind of driver that you have. Is this controled by a module? PCM that kind of thing. If the Pcm is your ground then not having enough resistence in the primary is going to be an issue.

Another way to look at this is. Can you insulate the Secondary better? Will a Cop from a different make work. The reason I ask is on ford trucks with the Cop it is a major issue that the shield on the secodary "leak" spark. And fire on to the wall of the head.

Also remember the Secondary mirrors the primary. you reduce voltage then you are going to reduce kv. that means you a going to have to change spark plug gap and maybe even the plug to a "cooler" plug to get the fire line straght.

Good luck