J&P Cycles Motorcycle Community

Participate in our motorcycle forums, view photos, and read up on our motorcycle tech articles.
Welcome to J&P Cycles Motorcycle Community Sign in | Join | Help
in Search
Latest post Mon, Oct 20 2008 11:26 PM by roger58xlh. 7 replies.
Page 1 of 1 (8 items)
Sort Posts: Previous Next
  • Thu, Oct 2 2008 11:51 PM

    Dual-plug Shovelhead Set-up

     I am mounting a set of dual-plug shovel heads on a '58 pan-shovel conversion with the stock manual advance circuit breaker, 12 volt. I need to add a second coil.  Can I use the stock circuit breaker with a second lead to the second coil or do I need to do some upgrades like a differnt capacitor or a dual-point set-up? It seems to make sense that the coils should handle both plugs on the left side and right ride rather than both plugs in the front cylinder and rear cylinder.  Any other changes?  Which coils work best? 5 ohm? Special plug wires?  Thanks for your help and advice.  (RTP)

  • Fri, Oct 3 2008 1:13 AM In reply to

    Re: Dual-plug Shovelhead Set-up

    Dynacoil has a 4 post unit that is just the same size as a standard EVO coil and it works.

    I've used it for 8 years in my dual plug 80 incher.

    Run the lowest resistence wires you can afford..........period..


    Nowhereman.....who else?

  • Sat, Oct 4 2008 10:17 AM In reply to

    Re: Dual-plug Shovelhead Set-up

     Thanks.  A good suggestion.  However, I'm using the stock manual advance circuit breaker; the DynaCoil four-poster is for electronic ignition with electronic advance.  I don't mind fitting two coils (one for left side, one for the right side), what circuit breaker format will work?  The popular consensus is to retard ignition timing about 5 degrees. Still stuck on how to fire the coils... RTP

  • Mon, Oct 6 2008 6:42 AM In reply to

    Re: Dual-plug Shovelhead Set-up

    The coils fire the front cylinder together and then the rear, not the left side and then the right.




  • Mon, Oct 6 2008 7:53 AM In reply to

    Re: Dual-plug Shovelhead Set-up

     Since you are using a single set of points this is a dual fire system. What you need to do is purchase two 3 ohm coils for electronic ignition systems. Part #'s 381-780, 381-216, 381-931 or 381-16.  Any of these will work as long as you wire them correctly. You would run your 12V + (from switch) to the terminal of one coils and the wire from the points to a terminal on the other coil. Next run a jumper wire from coil to coil on the two remaining terminals. This will give you a dual fire set up for dual plug heads. The reason you use electronic ignition coils is because of the 3 ohm primary resistance. When wired in this configuration you will end up with 6 ohms of primary resistance. Points systems generally need 5-7 ohms. This configuration will fire all four plugs at the same time.


  • Tue, Oct 7 2008 12:14 AM In reply to

    Re: Dual-plug Shovelhead Set-up

     bgrove,  Thanks. That makes sense.  Confirming: buy 3 ohm plug wires as well.  It would follow that the plug wires should match the resistance of the system, but its a 5-7 ohm, points-based system.  Comments?  Given the configuration you suggest, could you also just run two wires from the circuit breaker, one to each coil?   Also, another response suggested a front & rear bias rather than a right & left bias.  I can build a rational engineering-based case for either.  Comments?  Thank you all.

  • Tue, Oct 7 2008 7:17 AM In reply to

    Re: Dual-plug Shovelhead Set-up

     The spark plug wires do not come in 3 ohm. They are typically in the 300-500 ohm range. You do not have to match them to the points system. They will work whether you have points or electronic ignition. You will need one of our universal wire kits so you can cut the wires to length depending on where you locate the coils. P# 380-918 or 380-988 would be a good choice. You  can not run two wires from the points to the coils. This will change from being wired in series to parrallel. This would reduce the overall resistance from 6 ohms to 1.5 ohms and burn things up. Stick with the wiring method in my earlier response. These must be wired in series, not parrallel. Since you are firing both coils at the same time, it really does not matter which way you run the spark plug wires.


  • Mon, Oct 20 2008 11:26 PM In reply to

    Re: Dual-plug Shovelhead Set-up

     bgrove,   Thanks for your replies...you seem to have this issue aced.  'Much appreciated. As for placement, the stock location (for a '51 wishbone) on the seat down-tube and a second coil on a later model top engine mount with the coil bracket built in ought to get it done.   Thanks again. RTP

Page 1 of 1 (8 items)