Spark gap?

jpowell · Posted: March 12, 2009, 9:32 pm Post subject: Spark gap?

I'm sure this has been discussed elsewhere, but I thought this would be a good place to ask. I just finnished putting my new Iggi on. Fired up cold with the electric starter... (and on one cylinder cause I left one side hanging off) I'm quite impressed.. That being said, I bought the whole kit from mikes, coil n all. Does that combination fire a hotter spark? and if so, should I widen the gap? and how far?

Gotta say, you got a great product Pete. My only complaint would be I might have put a little heavier gauge wire on there, and when the jacket was stripped back the wires were nicked so I had to re-do it. No biggie though. Still well worth the $$$ and an awesome product.

pamcopete · Posted: March 12, 2009, 10:47 pm Post subject: Re: Spark gap?

jpowell

You could go to a wider gap becaus the coil does produce more voltage than the stock points coil, but the trade off may be in starting. There is no technical reason to widen the gap, however.

Glad you're happy with the product..... Smile

gantzcb · Posted: March 12, 2009, 11:20 pm Post subject: Re: Spark gap?

Jpowell,
In theory, correct me if I'm wrong, the length of dwell controls the saturation of the coil. So if you inrease the gap, when triggered to fire, greater energy is required to cross the gap, this shortens the burn time. If 6-10 KV is required to cross the gap and 3-4 KV is required to maintain the burn, the plug shuts off when the coil energy falls below the level to maintain the burn. In cars, wider gap and greater coil saturation is used to burn leaner mixtures. Generous Motors tried .060 gaps in the mid '70's, but like Pete said, there are problems cold engines - the spark finds its way to ground but not across the gap. As an additional note, plugs are designed to be gapped with a given range. I've got a PAMCO, not much run time yet, plugs gapped to stock spec.
Clyde

xsleo · Posted: March 14, 2009, 3:41 pm Post subject: Re: Spark gap?

If you use a coil that puts out 30 to 40 thousand volts, then increasing the gap can help. A .035 to .038 will work ok.
If you use a stock type coil with 10 to 15 thousand volt output then stock gaps should be used.
A hotter coil with a larger gap will give a larger spark, thus better overall running. If the gap gets to large then the coil can't jump the wider gap.

Retiredgentleman · Posted: March 14, 2009, 9:46 pm Post subject: Re: Spark gap?

I believe each coil will determine the best gap. Its good fun to experiment once in a while. Increase the gap a little and keep an eye on the plug colour, and how the bike starts and idles.

I've been using .038" gap, with points ignition and an Accel supercoil. I'll soon be switching over to the Pamco ignition, and will initially stay with that same gap.

pamcopete · Posted: March 14, 2009, 11:00 pm Post subject: Re: Spark gap?

Well, you need a higher voltage from the coil to jump a larger gap, but what you also need is a coil that produces that higher voltage with a relatively low internal resistance so that there is also a good amount of current in the arc. It's really all about the power of the arc, not just the fact that the gap was bridged. So, power is a product of both the voltage and the current in the arc. Higher power means a hotter spark. Hotter spark means more rapid onset of combustion and the ability to ignite a less than ideal mixture, which is the norm.

The primary reason that modern cars have a wider gap and correspondingly higher voltage to jump the gap has to do with the problems of igniting a lean mixture, brought about by the need to conform to EPA emission standards, and, lately, the quest for insane gas mileage. The wider gap exposes more of the mixture to the heat from the arc for better ignition of the lean mixture. Just think of the fuel / air mixture being drawn into the cylinder. It is not a perfect mixture. There are "pockets" of just air as well as "pockets" of just fuel molecules, so the larger the gap, the more likely that the arc will in fact actually contact both fuel and air molecules, and of the right proportion.

The need for the spark to contact both air and fuel molecules to start the fire is also true when an engine is under load. Generally, less fuel air mixture is drawn into the cylinder with the engine under load, which also means that there is less density of the fuel air mixture, so it's important for the spark gap to be exposed to a larger volume of fuel air mixture to ensure contact with the fuel and air molecules. So, a wider gap helps to produce more power when the engine is under load as well.

So, a wider gap is more efficient in igniting a lean mixture. Lean mixtures also occur when starting a cold engine, because the fuel does not atomize as well when cold, so a wider gap should help in cold starting situations. However, it is more difficult to produce the voltage necessary to jump a wider gap when starting because the starter motor draws the battery down. So, if you are going with a wider gap, you should also make sure that your battery and starter motor are in great condition, else the result could be more difficult starting with the wider gap.

I don't know if you all have seen it yet, but MikesXS is now offering a very high output coil with a secondary resistance of 15K Ohms. This new coil produces up to 75K Volts. The stock coil has a secondary resistance of 13 K Ohms but only produces about 20 Kv, so for a slight increase in secondary resistance, you get a huge increase in voltage. That means that this coil not only produces a very high voltage, but it has the current as well to produce the power that is converted to heat in the combustion chamber.

With that much voltage at 14 volts on the primary, this coil will provide more than adequate power when starting with a reduced battery voltage, so you can widen the gap without compromising starting ability.

Retiredgentleman · Posted: June 27, 2009, 10:38 pm Post subject: Re: Spark gap?

Just an update on my ignition/coil. I switched over from points to Pamco this spring, and still using the same Accel supercoil. My bike ran well with the points and Accel coil, and continues to run well with the Pamco. Very nice now that I don't have to check points for wear, set gaps etc.

Here's a pic of my ignition in action; now using .035'' gap for the plugs.

What Happened to 650rider.com?

Yamaha xs650