Dyna coil broken?

Hello all, I have a 77 KZ650, and today I was riding around and the bike seemed as though it was running on two cylinders. Got it home somehow, and started to diagnose. Long story short, measured the secondary resistance of the "bad coil" and it measured 21K ohms. The "good one" measured 14.3K, and my question is, does this mean my coil is shot? Thanks...

big_c_snow wrote:

Hello all, I have a 77 KZ650, and today I was riding around and the bike seemed as though it was running on two cylinders. Got it home somehow, and started to diagnose. Long story short, measured the secondary resistance of the "bad coil" and it measured 21K ohms. The "good one" measured 14.3K, and my question is, does this mean my coil is shot? Thanks...

Hello, Chris, and WELCOME to KZR!
We're glad you're here!

The coil may be okay.
Different resistance may be inconsequential, or perhaps result from variance in resistors inside the spark plug caps.

With engine at idle rpm, would spray water mist onto exhaust header pipes to confirm which cylinders aren't combusting.

The spray will sizzle and instantly vaporize on an exhaust pipe from a combusting cylinder.

The spray will run down the exhaust pipe from a non-combusting cylinder.

Many conditions may result in combustion failure.

Could start with removing spark plugs and visually observing spark while spinning over the engine. Look for fat blue sparks. Not thin orange sparks.
Repeat test with brand new spark plugs of (per factory specs), perhaps NGKB8ES.

Good Fortune!

It won't idle, so I can't really do the first test... I put brand new plugs in it, and it did the same thing. Checked for spark, and 1 and 4 had nothing, 2 and 3 had normal good looking spark. The bike has Dyna ignition and coils, and regular spark plug wires, no resistor caps.

big_c_snow wrote:

It won't idle, so I can't really do the first test... I put brand new plugs in it, and it did the same thing. Checked for spark, and 1 and 4 had nothing, 2 and 3 had normal good looking spark. The bike has Dyna ignition and coils, and regular spark plug wires, no resistor caps.

Is battery+ voltage reaching the 1/4 coil primary terminal?

One possibility might be failure of signal from left-hand Dyna-S module, for whatever reason, which is supposed to continuously ground and un-ground the coil primary winding, which allows the coil to charge-fire-charge-fire- . . .

It would be a good idea imo to first assure that the coil is receiving battery voltage with ignition switch in ON position.

Good Fortune!

Would also assure that the coil primary terminal screw head is not shorting against the metal coil mounting spacer.

Good Fortune!

When wiring up the ignition coils, for best results use electrical terminals rated for the size of the wire.

From the picture Patton shows, it looks like a 10 gauge ring terminal with a 3/16" diameter mounting hole has maybe a 16 gauge wire going to it. It might work if the wire insulation is removed about twice the distance and then the conductor is doubled over and crimped, but if it were me, I'd get the proper terminals for the job.

Also using the correct crimping tool makes a big difference in conductivity. Never use vice grips or regular pliers to crimp the terminals.

The terminals are color coded to meet the AWG(American Wire Gauge).

RED,22-18 gauge, probably used for low current needs.
BLUE,16-14 gauge, medium current needs,8-10 amps
YELLOW,12-10 gauge,probably 20-30 amp requirements
RED,8 gauge,used for battery terminal wiring.
BLUE,6 gauge, much higher current capabilities.

I could cover more conductor sizes, but what I've listed will work on most motorcycles.

AWG wires are backwards to what people might think in size,the higher the number, the smaller the size of the conductor. So 16 gauge is many times smaller than 10 gauge.