Author Topic: Ignition Coil/Cap Resistance  (Read 97 times)

kevin g

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Ignition Coil/Cap Resistance
« on: October 12, 2019, 01:34:34 PM »
I am working to improve the starting of my 83 Vision and have narrowed it down to the resistance of the coils/caps to the spark plugs.

Now I am getting conflicting information on what the resistance should be.  I have searched all over this site and find no specific answer.

The Yamaha and Haynes manuals both say the resistance from the orange coil lead to the plug cap should be 7.9KΩ 20%.  I have six different coils that measure in this range with NO plug wires.  The plug caps on my bike measure 10KΩ for a total resistance of about 20KΩ.  I think my caps are original.  I find information on this site that implies that the caps should have 5KΩ resistance and that is were I find the conflict.  If the plug caps are supposed to be 5KΩ then the total resistance of the secondary would be 12.9KΩ (7.9K + 5K) which is above the specified resistance.

All of this implies that the plug caps should be 0Ω resistance.

One thread on this site I found stated the NGK plug cap should be VB05E which is 5KΩ.  I happen to have two of these in a big collection of parts I just bought for the bike so I will try them and see if things improve.

My trouble is that the front cylinder does not want to fire when cold and only catches after the rear runs a while.  I am an EE (and often very particular) so this conflicting resistance information is driving me nuts.

Does anyone have a precise answer to what the secondary TOTAL resistance should be with coils, wires and caps?

George R. Young

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Re: Ignition Coil/Cap Resistance
« Reply #1 on: October 12, 2019, 08:36:00 PM »
From another EE:

The manual says the coil secondary should be 7.9 K-Ohms sans caps, probably another 5K-Ohms for the cap.

Another thing to look at is the pickup coil.

jefferson

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Re: Ignition Coil/Cap Resistance
« Reply #2 on: October 12, 2019, 08:40:18 PM »
Is it possible that the enrichment passages for the front cyl. might be plugged? I do know that on my 650 Seca the 2 outer cyl plug caps resistance was too high and the new caps made a big improvement in how lively the motor was. I don't remember it changing the starting however. The inner 2 that were out of the elements were fine.
I was also going to question if that figure was to the cap or after the cap. George evidently looked it up. Good going.

fret not

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Re: Ignition Coil/Cap Resistance
« Reply #3 on: October 13, 2019, 04:00:07 AM »
We are assuming the battery is in a good state of charge.
Retired, on the downhill slide. . . . . . . . still feels like going uphill!

kevin g

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Re: Ignition Coil/Cap Resistance
« Reply #4 on: October 13, 2019, 11:56:10 AM »
The battery is fully charged, brand new, etc.

I will be re-checking the carburetors to ensure the enrichment circuits are clean.

Back to the ignition resistance:
The pickup resistances are 115Ω and 117Ω so they are in spec.
Please show me in what manual it says "sans caps".  Both the Yamaha and Haynes manuals have the same diagram showing the meter connected through the cap.  The Haynes has a passage in it to check the cap itself but all it says is to replace the cap if it reads infinite resistance.  I replaced the 10KΩ caps with 5KΩ caps and there was no change in the starting behavior.

I am going to concentrate on the carburetors because that is where the symptoms point me.  The ambiguity in the ignition resistance specs is annoying.  I will probably get a spark gap tester just for piece of mind.

Prophet Of Doom

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Re: Ignition Coil/Cap Resistance
« Reply #5 on: October 13, 2019, 09:23:45 PM »

I'm with you Kevin, the 11J, 16R, and 11U manuals all state the secondary resistance includes the lead and plug cap, but I don't believe it either.


I just happen to have 4 coils on my bench - 2 of them known good from my (previously) running bike with replacement caps and leads.  The other two have original caps and leads.


All 4 coils measure 8.2KΩ - 8.5KΩ and 21KΩ-25KΩ @15 Deg C including wires and caps. 







George R. Young

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Re: Ignition Coil/Cap Resistance
« Reply #6 on: October 13, 2019, 09:25:12 PM »
. . . Please show me in what manual it says "sans caps".  . . .
I was going by this from the factory manual, I agree the diagram is confusing.

kevin g

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Re: Ignition Coil/Cap Resistance
« Reply #7 on: October 19, 2019, 10:25:02 AM »
Problem solved.  It was not ignition related.

I found that one of the idle(?) fuel passages in the carburetor was plugged.  It is a passage at the bottom of one of the cast tubes that lets in fuel from a small bore right next to it.  There seems to be a tiny brass jet in there that is pressed in and cannot be removed.  I used a guitar string to clear it out (after trying air, solvent and other things).

After putting it all back together the bike fires up instantly.  Now all I need is some brakes...

WGuaire

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Re: Ignition Coil/Cap Resistance
« Reply #8 on: October 19, 2019, 12:20:10 PM »
Good job!
  EBC FA81 x 2 for the front.

jefferson

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Re: Ignition Coil/Cap Resistance
« Reply #9 on: October 19, 2019, 07:47:34 PM »
And stainless braided lines are a must as the stockers are beyond old.