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Sorry, another coil question *I searched*

  • Thread starter Thread starter EdgeGrip
  • Start date Start date
E

EdgeGrip

Guest
1977 GS 750, Dyna ignition system and stock coils, NGK caps.

Seemed to run ok a couple weeks ago, but it has been a slow project so I don't often start it. Tried starting it in the cold the other day, couldnt get anything. Tried starting it today (Warmer), couldnt get anything. Not even a cough. Took the caps off 1 and 4, no spark. Searched, found out it could be coils.

I meter'd the following:
Voltage drop is less than .5 volts (batt is 12.4 after a lot of starting attempts) and at the wires to the coils (disconnected) it was 12.0x or so. Thats from battery to the end of each wire to the coil.

Primary resistance (terminal to terminal on the coil right?) ~ 4.3 ohms Thats both coils.

Secondary resistance (plug cap to plug cap right??) ~ 23,500 ohms on the 2 /3 coil, and here is the kicker...it wont even read the 1 / 4 coil. At one point I had it reading around 200K ohms...whats the deal here?

So, again, whats the deal with 1 / 4 not even registering? Obviously its bad since Im not getting spark but what would give it infinite resistance? Im not an electrician so bear with me. Also, 23.5 kO's on the other secondary seems low. Will low hurt anything?

I know Im going to have to buy coils, just curious about some of those readings.

Thanks.
 
you say you have no spark on 1 & 4 plugs, do you have one on 2 or 3?
sounds like the 1&4 coil is toasted.
get some nice Dyna coils to go with the ignition system
 
I recently had a similar problem with my stock coils (gs1150). Coils were turned out to be fine. I had corrosion in the wire/cap connection and inside the caps themselves. Plus one bad cap. If possible try checking all the pieces individually.
 
If you have the original wires on the coils, you might get some cracking and voltage leaks through the wires. If the NGK caps were put on and the old wires not snipped off, then a great deal of corrosion and lack of contact can occur.

As dorkburger suggested, take the caps off the 1 & 4 spark plug leads and test their individual resistance, and also the resistance across the plug leads. This should highlight where the break in the conductor is. If it turns out the caps are fine and the leads are providing the resistance then:

snip off about 1/4" of wire, and check the resistance again. If you are back to normal, then remount the NGK caps, and go.

For what it is worth, I have had instances on my 650 where only one plug cap/lead was a problem, and the bike would start hard, or not at all.
 
Thank you guys.

I honestly didnt check the 2 / 3 coil for spark. I just took everything apart to read it with a meter. The plug caps checked out fine, they are all brand new. I did not snip off the ends at first, but after reading here a bit, I snipped off ends of the plug wires about 3/16" or so then stuck the meter needles directly into the plug wires. The 2 /3 read about 12.5 kO's and again, the 1 /4 wouldnt even read. (except that one time mentioned above when it was like almost 200 kO's). The 1 / 4 coil does have a plug wire thats loose at the coil...Thats why I am assuming its just bad.

I guess part of my question was this: WHY does low secondary resistance creat a problem? I can understand high resistance of the primary side being an issue.

Thank you.
 
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