Topic: Weird situation with my coils

[zackblack]

ok so here goes -

I've red everything on how to check the coils with a multimeter to see if they are bad.  I check the small wires (yellow/blue and black with white stripe) and get a reading of 6.  I check the two large wires that attach to the plugs and I get nothing - zero - zip!  Coils are bad right? I thought so too...

Just for giggles I go out and do a spark check (hook the coil up directly to the battery and hold the plugs together to see if they spark) and I still get no spark! Coils are bad right? I thought so too...

So just because I'm anal about this stuff I check the plugs wires with the multimeter again aaannnddd - I get a reading!

So are BOTH coils shot (they both act this way) or am I crazy?

PS: Factory (40 year old) coils and the OP says the bike ran when he parked it (no reason for him to lie - he gave me the bike for free)

[zackblack]

Bump

[raymond10078]

I wouldn't measure through the spark plug caps.  Remove them and measure through the wires.  Caps go bad.

Also - you don't mention values - like - is it 6 ohms?  What type of meter?  If it is an analog, are you changing the scale?

Your spark test - its better to do it the way the manual says - take the to spark plug leads (minus the caps), and hold them about 1/4 or so apart, then connect/disconnect power to the coil inputs - you should see a spark.  You can test with plugs, too, but they have to connected together (ground to ground).  Still, I'd remove the caps first.

[zackblack]

Power is getting to the coils

Tried the "hold the wires apart while cycling power" - still no spark.

I'm thinking it's a points/condensers issue...

[HondaMan]

Hmmm...now you've confused me...

Check the ohms, like you have, between Bk/Wht and Yellow (or Blue), should read 4.4 to 4.8 ohms on the 500/550 coils (400:1 winding ratios).
Remove the sparkplug caps, then check from one spark wire to the other (like #1 to #4, or #2 to #3). It should fall into the range of approximately (4.6 ohms x 400)=1800 or so ohms max, give or take a couple hundred ohms. The usual failure mode is a broken wire inside one of the spark wires, at the coil inside the molded-in joint. It is exceedingly rare for them to short turns, which will make the reading less than, say, 1200 ohms, but I have seen it twice in these 40 years. The latter shows up as no spark after the coils are hot, while the former shows up as no spark at all or else very marked cold-bloodedness until the engine is well hot (and nasty in the wet!).

But, ALL these tests are done without power, and with the wires disconnected from the bike. RS meters are also notorious for their inaccuracy: even the $2 Harbor Freight meter is better than most of the RS meters I have had or used, when measuring ohms.

[zackblack]

@Hondaman

I'll take a picture of the MM when I do the checks again tomorrow and then post them.

[zackblack]

Ok so here are the Pictures:

The first one is a "resistance" check (according to my MM manual) of the blue wire and the black wire with the white stripe.

The second one is also blue/balck W/white but with my meter set to 2k (this is the only setting that wouldn't give me a reading of 0.00)

The third one is uncapped wires with my meter set to 20k

The fourth one is with 5ohm resistor caps and with my meter set to 20k

[zackblack]

Here are some more pictures.

NOTE: The other coil (yellow and black with white stripe) reads exactly the same.

[raymond10078]

The primary resistance looks fine.

What is the secondary resistance of the other coil?

I'm doubtful that you can use a "turns ratio" to determine expected secondary resistance, since the gage of the wire will differ between the two windings.

In addition, the Honda manual identifies the turns ratio as much lower than 400.  420 turns primary, and 13,000 turns secondary.

Since you have two coils, I'd first compare them to each other.  Your readings look OK (to me).  I've searched high and low for secondary resistance readings, and can't find them in a Honda manual.  Every Honda manual I've seen so far only validates that the circuit is not open.

By the way, is it normal for a meter to show 0.00 when using a 2 Megaohm scale, and the resistance is 6 ohms.  Same for other higher scales.

[zackblack]

ok so the other side (2-3) reads almost the same as the pics I took for the first side (1-4).

The caps for 2-3 are reading WAY higher (they are much older) so I'll be replacing them.

When I put power to the coil while holding the threads of the two plugs together i can hear a spark (I hear it at the tip of the plugs where I should be seeing a spark) so I put my battery on the charger and then I think I'm going to get one of those in-line spark detectors and see if I truly am getting a spark.

[raymond10078]

You could try your test in the dark - or at least not in bright light.  If I recall correctly, the spark should jump an 7 or 8 mm gap (coil lead to coil lead).