dual plugged head

[D-Day]

OK boys and girls.  I just bought a used motor and it has been dual plugged.  Anyone know if the ignition has to be retarded, or what the advantages or disadvantages of this modification are.

[sprint_9]

It should burn the fuel more completly and overall should run a little better, but one disadvantage would likely be more heat, but you could throw some more fuel at it to help cool the engine.  Post up some pics of it, I want to see where they put the other plug.

[Rema1000]

Use colder plugs (NGK 5329 ... they used to be called DPR9EA-9) to cool it down a little; or just add some ethanol .  Dual plugs with staggered timing sounds perfect for burning ethanol (along with domed pistons and shaved head).

[dgyver]

I was talking to my machinist about this when he was boring some cylinders for me. It came up since he was relocating a plug in a vintage race bike. If it is where I think it is, vertical next to the valve cover, this will provide a more even and complete burn of the fuel. I would run another pair of coils (or dual plug coils) so they fire at the same time and leave the timing the same.

[D-Day]

It should burn the fuel more completly and overall should run a little better, but one disadvantage would likely be more heat, but you could throw some more fuel at it to help cool the engine.  Post up some pics of it, I want to see where they put the other plug.

I will post a picture of it mid week.  I am off to a wedding in a few minutes.

[D-Day]

I was talking to my machinist about this when he was boring some cylinders for me. It came up since he was relocating a plug in a vintage race bike. If it is where I think it is, vertical next to the valve cover, this will provide a more even and complete burn of the fuel. I would run another pair of coils (or dual plug coils) so they fire at the same time and leave the timing the same.

Yes, the second plug is vertical.  I am surprised it fits between the valves.

I will be taking the top end of the motor apart before I run it.  I wonder what other goodies I will find.

[mjm]

OK boys and girls.  I just bought a used motor and it has been dual plugged.  Anyone know if the ignition has to be retarded, or what the advantages or disadvantages of this modification are.

As I recall, one of the advantages of a dual plug set-up is that you can advance the timing more without detonation.

[dgyver]

I will be taking the top end of the motor apart before I run it.  I wonder what other goodies I will find.

Curious what size pistons are in there, and what profile. High lift cams too?

[Mk1inCali]

I know this doesn't help any, but my dad just picked up a '72 CZ380 motocrosser, and it's got dual plugs.  Slightly different purpose though... :lol:

[werase643]

and what is that slightly different purpose......

2 stroke singles with a spare fouled plug.....
       

[Mk1inCali]

Indeed!

A popular mod before the digital ignition times was to run 2 coils and fire both at the same time, for all purposes listed above for the 4-strokes, but the new ignitions light hotter, faster and are obviously more reliable.

Don't even need to go to a reed valve anymore with the quality of mixer oils out there today to prevent load-up.  It actually idles like a modern MX'er, and that's pretty darn impressive in my book.