The reason a split fire doesn't work is easy.
1. You have a coil that is designed to send one spark of a white to light blue flame now you are asking the same coil to through two of those it is not going to happen!!!! It is usually orange to blue flame unless you have a high powered coil to deliver more power.

2. If you have a freind with split fire or have one take it out and hold it up to the motor so you can see the spark now turn it over and you will see what I mean then do the same with a regular plug.

3. You usually only get one spark any way.

 

Well that’s not really what happens...
86Atc250r said it best. "The spark follows the path of least resistance, PERIOD."

A single spark trying to jump two gaps is more resistance .since the spark follows the path of least resistance; the electricity will only go to one electrode at a time so the spark energy should be the same. The design behind them was a single electrode split in two would allow the flame /spark kernel to be more exposed to the fuel/air mixture. But it doing so the electrodes had to be made thicker to prevent them from heat damage... it kinda like beating a dead dog. Even though they have exposed the flame kernel the dead electrode (the one that the spark is not traveling to) will block it. Doing the opposite of indexing
Now if the plugs fired like in the pic on the package well that would be pretty good but since it does not they are a waist of money.
Learn to index plugs on 4 strokes and save your money.

Indexing is marking the plugs and aligning them so the open side of the ground strap /electrode is aimed at the center or away from the incoming fuel air mixture to increase power and efficiency

 

The 400EX ran WORSE with the Splitfire than with the stock plug!! Save your money.

 

I agree,had one in an old quad years back,thank God they had the 30 return policy,got my money back,ran worse,and would foul easier.

Should have named them Sh!tfires,would be a lot more accurate.