Testing total coil resistance

Hi all, been awhile. Finally got around to installing the twin PWK's from Jim Schmidt as well as rewiring the old girl. All seems good except I still have a fouling plug on the timing side. Redoubled the carb settings, float height, synchronization etc... all good. Now, knowing that 95% of carb issues are electrical, and considering I've freshly rewired her, new boyer and am getting a solid 12.8 - 13.4 out of the sparx three phase... the only thing left for me to look at is the coil/plugs/plug wires combo. Running a dyna dual output 5 ohm coil. Now this is where I'm confused, I've tried several different combo's listed below:

- copper core w/ non resistor caps and resistor plugs = 4.8 ohm, both wires, from plug tip to coil end
- non copper core w/ resistor caps and non resistor plugs = 9-10 ohm, both wires, from plug tip to coil end
- copper core w/ resistor caps and non resistor plugs = 13-18 ohm, both wires, from plug tip to coil end
- non copper core w/ non resistor caps and resistor plugs = 8-10 ohm, both wires, from plug tip to coil end

My question is, how do I get an accurate ohm reading out of the entire ignition setup (coil + wires)? Is it just a matter of plugging in the wires with the plugs attached and reading from plug tip to plug tip? Thanks for your help!

I thought the resistance rating on the coil was supposed to be the low voltage side? Guess I will watch and learn.

Russ

acadian said:

My question is, how do I get an accurate ohm reading out of the entire ignition setup (coil + wires)? Is it just a matter of plugging in the wires with the plugs attached and reading from plug tip to plug tip?

Click to expand...

I don't follow your thinking?

Why do you think the variation between different plug/cap/wire resistor/non resistor combinations is important?

The coil ohms rating (5 ohms) generally refers to the coil's primary circuit resistance.

Your ohms readings appear to be incorrect, as a resistor plug or resistor cap would normally have a resistance of 5 kOhms (5 kilo Ohms = 5,000 Ohms) so I think your readings are probably kOhms (x1000)?

"Non-copper" wire is a bit meaningless, do you mean "resistor" wire (which is typically around 3 kOhms per foot)?

L.A.B. said:

acadian said:

My question is, how do I get an accurate ohm reading out of the entire ignition setup (coil + wires)? Is it just a matter of plugging in the wires with the plugs attached and reading from plug tip to plug tip?

Click to expand...

I don't follow your thinking?

Why do you think the variation between different plug/cap/wire resistor/non resistor combinations is important?

The coil ohms rating (5 ohms) generally refers to the coil's primary circuit resistance.

Your ohms readings appear to be incorrect, as a resistor plug or resistor cap would normally have a resistance of 5 kOhms (5 kilo Ohms = 5,000 Ohms) so I think your readings are probably kOhms (x1000)?

"Non-copper" wire is a bit meaningless, do you mean "resistor" wire (which is typically around 3 kOhms per foot)?

Click to expand...

They were askew, I just found a testing sheet from Dyna's site and the coil's primary and secondary resistance check out (5.2/17.5). So the coil is fine. As for my plug/wire combo question, just trying to settle in on the correct resistance for the boyer. When running resisted caps w/ non resisted plugs she ran like shite. Switching to resistor plugs and non resisted caps provided much better results. Guess I'm a bit confused myself...

acadian said:

When running resisted caps w/ non resisted plugs she ran like shite. Switching to resistor plugs and non resisted caps provided much better results.

Click to expand...

Either should work equally well? I suggest you measure the caps to check if they are actually 5 kOhm? Did you try another pair of non resistor plugs?

What type of Boyer is it?
The analog/ue Boyer Micro MkIII or MkIV ignition shouldn't require any spark resistance at all, unlike digital ignitions (Boyer Micro Digital, Micro Power, Tri-Spark etc.) which must have 5 kOhm caps or plugs, however the Sparx reg/rec box needs 5 kOhm resistor caps or plugs in order to function properly.

L.A.B. said:

acadian said:

When running resisted caps w/ non resisted plugs she ran like shite. Switching to resistor plugs and non resisted caps provided much better results.

Click to expand...

Either should work equally well? I suggest you measure the caps to check if they are actually 5 kOhm? Did you try another pair of non resistor plugs?

What type of Boyer is it?
The analog/ue Boyer Micro MkIII or MkIV ignition shouldn't require any spark resistance at all, unlike digital ignitions (Boyer Micro Digital, Micro Power, Tri-Spark etc.) which must have 5 kOhm caps or plugs, however the Sparx reg/rec box needs 5 kOhm resistor caps or plugs in order to function properly.

Click to expand...

Analogue Boyer w/ sparx three phase. Tested the resistor caps and they checked out yet the bike ran shite with them in, wasn't until I switched to the resistor plugs/non resisted caps that she caught her groove. Can't explain. Just ran another test, the resistor plug/non resistor combo show 4.8 ohm each, grounded them both side by each on the head and kicked her over, nice bright blue spark on both... maybe I have a crack in one of the wires that's not showing up until she's shaking and rolling?

acadian said:

Just ran another test, the resistor plug/non resistor combo show 4.8 ohm each,

Click to expand...

If you've got a resistor plug then it can't be 4.8 Ohms as a resistor plug or cap should measure 5,000 Ohms.

acadian said:

maybe I have a crack in one of the wires that's not showing up until she's shaking and rolling?

Click to expand...

As the spark plugs are at opposite ends of the same piece of wire in a dual coil, then a fault in one component is likely to affect the sparks of both plugs.

L.A.B. said:

acadian said:

Just ran another test, the resistor plug/non resistor combo show 4.8 ohm each,

Click to expand...

If you've got a resistor plug then it can't be 4.8 Ohms as a resistor plug or cap should measure 5,000 Ohms.

acadian said:

maybe I have a crack in one of the wires that's not showing up until she's shaking and rolling?

Click to expand...

As the spark plugs are at opposite ends of the same piece of wire in a dual coil, then a fault in one component is likely to affect the sparks of both plugs.

Click to expand...

Well, I'm obviously reading it wrong then because that's the reading with 4 different wire combos, either that or I'm not taking readings from the correct points.

You've got at least two problems:

- As Les and others have pointed out, a resistive cap or a resistive plug must measure 5 kOhms, within a few percent, from top to bottom of each device. If you're not measuring 5 kOhms, you've got a serious meter or technique problem.

- All plugs are shipped with a metal hat that screws onto the upper post (the anode). Some caps are built to mate to the hat, and some are built to mate to the post. Failure to sex it right will result in an intermittent connection between the plug and the cap. Sounds to me like one of your combinations is intermittent.

acadian said:

Well, I'm obviously reading it wrong then because that's the reading with 4 different wire combos, either that or I'm not taking readings from the correct points.

Click to expand...

Unless you can tell us what your meter range and resolution is, then it's difficult to say-but I suspect your meter is reading Kilo Ohms so 4.8 kOhm (4,800 Ohms).