Weak Spark! Help please

[Motorheaddad]

Ok, so I have a weak spark on cylinders 1&4. I did the coil relay mod hoping that would help, but it didn't. I was about to buy another coil on (st)E(al)bay but thought I would ask you guys if there are some tests I can do to make sure it's the coil. I don't want to start shot gunning parts at it. So if you guys can steer me in the right direction I would greatly appreciate it. Thanks in advance.

Steven in sunny San Diego

[Pat Conlon]

Hey Steve, I'm in Leucadia and it's definitely not sunny....been raining since noon.

Yes, there is a test you can do on the primary side and secondary side of the coils.
Unfortunately, I do not have my shop manual with me....

Stay tuned, someone will chime in with the test specs.

[movenon]

Coil primary side 2.7 ohms +- 10%
Coil secondary side (plugs side) 12,000 ohms +- 20%.   (9500 to 14500 ohms)

That's at 68 degrees...... 

Hope it helps.
George

[Motorheaddad]

Cool! I'll test it in the morning!

[Motorheaddad]

Ok, so I have 2.8 ohms on the primary side for both coils, but it shows open on the secondary for both coils on all leads. I've measured every which way and on all ohm setting on my meter and it still shows open. Is it possibly for the coils to fail these tests but still provide a spark? I'm confused! I need a beer!

[Pat Conlon]

How are you reading the secondary?

[Motorheaddad]

First across both terminals at the plug for primary and from either wire (I tested from both just in case) at the plug to the end of the spark plug cable. I'm gonna see if maybe I have a bad connection at the boot. I'm assuming that would give me a weak spark if it has to jump a gap before it gets to the plug. Hopefully that's it cause I wanna ride this thing.
I tested like this:
https://www.youtube.com/watch?v=rRQ45lT2d3c

[Fj.itis]

I may be wrong but i test mine from lead to lead on the same coil its the only way i could get a reading.

[JoBrCo]

That is not the way you check the secondary.  That youtube video seems to be wrong, unless it's bike specific, but I don't see how.

The primary coil is not physically connected to the secondary.  In essence these things are just transformers.  The primary sends voltage to the secondary via inductance.  Meaning electromagnetic force (through the air) due to their proximity.  The voltage seen on the secondaries depends on the number of turns and the gauge of wire in both the primary and secondary coils. Their are two primaries and two secondaries according to the Yamaha service manual.  To check the secondaries connect your ohm meter between 1 & 4 and 2 & 3 you should get the values George specified.

Ensure you don't have power on the primary when you're checking the secondary, your checking resistance in ohms not voltage, (that would be fun), Not! 

FJ Forever!  


JoBrCo

[movenon]

The manual shows measuring at the plug wire ends, not including the plug caps.  The cap has resistance in it.

I don't remember the wire size but the plug wires are replaceable.  They are solid wires (non resistive) and available off the shelf from NAPA.  Randy stocks the plug caps if they need to be replaced.
George

[movenon]

This might help Steve.  You will have to click the full page magnifier to enlarge the image.

http://www.fjowners.com/index.php?action=gallery;sa=view;id=7545
George

[Motorheaddad]

Ok, tested it the right way and my reading were spot on. I measured without the boots, so I thought i would measure with the boots and man my meter started jumping all over it finally went to open after about 100,000 ohms. What the heck!?!? Are my boots the issue? Is that possible? Does anyone know if there is a resistance reading for the boots?

[movenon]

Ok, tested it the right way and my reading were spot on. I measured without the boots, so I thought i would measure with the boots and man my meter started jumping all over it finally went to open after about 100,000 ohms. What the heck!?!? Are my boots the issue? Is that possible? Does anyone know if there is a resistance reading for the boots?

Plug cap:  10,000 ohms (10K) + - 10%. 
George

[Motorheaddad]

Well I think I figured it out. Two of the boots measure at 9,800 ohms consistently, the other two didn't do so well. One of them reads 9,800 but the moon has to be aligned perfect if not it goes crazy and finally reads open, the other one reads open, I thought I saw a flicker at point when I was wiggling the probe but i think that was hope messing with me. Anyway, I know Randy has OEM and NGK. Will the NGK's work with oem coils and cables? Just trying to save some pennies

[Pat Conlon]

Yes, the NGK's are resistor boots and work well with the stranded oem FJ plug wires.

Twist the old boots off. Trim about 1/2" off the oem plug wires so when you twist on the new NGKs the point bites into fresh conductors on the plug wire.

Those oem FJ plug wires seem to be indestructible. I'm still on my oem set at 180k miles, although I have new NGK boots.

Glad you got it figured out!  Cheers. Pat