Spark plug Science experimentation Hawk 250

[Ghenghis]

Bought a Hawk 250 a couple months ago, red with black rims, reading posts from here and watching MotoCheeze's videos won me over.

I had a late 70's Yamaha 125 Enduro a long time ago, got it used when I was 13, learned how to replace and adjust the points/condenser I ordered out of the JC Whitney catalog as it would hardly run when I got it. Crazy to think that we had to actually ask someone, usually a friend's mechanic dad, or an uncle, how to fix things. I rode the wheels off that bike, the wheels never actually came off but the muffler began to form rust holes on the outer skin. Had to leave it behind when we moved from the country into the city, it had broken down so I didn't get much say in the matter. I've always wanted to get another Enduro, the ability to do some light off-roading and legal street driving always seemed like a win win.

Finally, nearly 30 years later I decided to get another Enduro. I've always had an interest in anything mechanical, I had to know how it worked, and what I could do to make it better. I'm an information sponge, so I know at least a little bit about everything. My Hawk doesn't have 20 miles on it yet and I've had the carburetor off at least 5 times now, modded the airbox, and currently waiting on a jet kit/spark plug to arrive from Amazon. As of now I daytrade stocks and fix computers, recently decided I wanted to learn trading, so far one job is financing the other, I'm sure you can guess, I am getting better though.

I've soaked up quite a bit of info on mods for the Hawk and decided I'd delve a bit deeper into the combustion process and how I can enhance it. I came across some goofy looking plug called an E3 something, it claims to increase all kinds of good stuff, I stared at it for a minute and called bs on those claims. This got me searching for the sciency parts, not the "it runs so much better now" reviews. There's no way this plug can help, and now I know why. I'll get you started with some actual data acquired by proper experimentation.

http://www.sciencedirect.com/science...90447912000883
The link looks a bit weird, I guess we'll see if it works once this is posted.

I'll give some facts I've learned on the subject up front, the article is a bit lengthy. The abomination called the E3 spark plug looks like someone welded half a thimble onto the sparky end of it. I'll try to link it here.
https://www.amazon.com/E3-Spark-Plug-E3-36-Powersports/dp/B0022ZAFOC/ref=sr_1_5?ie=UTF8&qid=1477232338&sr=8-5&keywords=e3+spark
First off I'll give you some info on what's called "flame quenching", this is the effect of the cooler spark plug electrode and ground strap interfering with flame propagation at the exact point of ignition in your compressed air/fuel charge. Spark plugs do a very good job of conducting their heat into the engine block, this happens so your next incoming charge doesn't hit a bright white hot spot of metal and ignite before it's supposed to, also it keeps your spark plug from melting and introducing new parts to your engine you'd rather not have. The spark from your electrode tip to the ground strap is very small and takes the shortest path with the least amount of resistance, go ahead and put those advertisement pictures out of your mind, the ones that look like a ball of plasma forming around the electrode and ground strap, or the ones with 2 to 4 neatly arranged ground straps. The first point of ignition once the spark leaps from the electrode to the ground is a tiny little area between the two, combustion begins here and propagates outward, some of it's energy needed to cause a reaction in the surrounding particles is absorbed into the cooler ground strap and electrode, slowing this process and causing an uneven shockwave to form outward from this point until all air/fuel is reacted. What you really want is that explosion to travel equally outward with nothing in the way to absorb it's energy or break up it's wavefront as that ends up burning your fuel slower, which causes it to lag behind the perfect crank position to give you maximum cylinder pressure on the downward power stroke. The position at which the combustion begins should be as close to center of it's surrounding volume as possible for best results in efficiency and power. This is why you see spark plugs with the longer electrode end, it gets the spark closer to the optimal chamber position for ignition.

There's more! You don't need colder series plugs unless you're running forced induction or other means of extreme cylinder pressure. A colder plug transfers cylinder heat "energy" into the head faster than a warmer plug. With higher pressures you have higher temperatures, the colder plug is designed to keep the ground strap/electrode from melting in a more extreme environment, and pre-detonation. Very few setups benefit from a colder spark plug. A cold plug will also foul out quicker as it isn't hot enough to burn off the residue remaining from the combustion cycle, causing some to think they are running the engine too rich when inspecting the spark plug.

Finally to the spark. Electricity always takes the path of least resistance. A generic or standard spark plug normally has a decent sized round flat electrode and flat square ground strap, they call this the J plug/design. The electrode end needs to be a certain size depending on it's properties "iridium/platinum/cheapium" to survive cylinder temperatures without melting. The more exotic metals have a higher melting point, this allows them to be smaller, which increases flame propagation area, and lowers surface area to decrease electrical resistance for the spark jump. Resistance also increases along with higher atmospheric pressure, aka, your compressed fuel charge.

I think you've got the bulk of the info, now for the fun stuff. You can sidegap your spark plug by cutting back the ground strap, opening up the ignition area for a more optimal burn. The power of your ignition, pressure in your cylinder, and resistance of the electrode material determine how wide you can set your gap. The electricity builds up on the end of the electrode until it can overcome it's surrounding resistance then jumps to the nearest ground. A wider gap creates a longer spark and a larger initial ignition area, too wide and it may fail to spark or slightly delay until it can overcome it's surrounding resistance. Cool stuff huh. A little experimentation for possible increased efficiency and power can't hurt, right? Plugs are cheap to replace if one happens to expire during clinical trials!

You can also completely cut off the ground electrode, some plugs are made this way, they are called flat gap plugs, the above linked test results show this plug type performing above all others in it's ability to create higher cylinder pressure due to quicker/more even flame front. I know, it sounds crazy to cut off the little J ground strap completely, and I wouldn't advise anyone to immediately go out and do this unless they have a backup plug. Back to the spark travel and resistance I talked about earlier, if the electrode is sticking out pretty far past the base of the plug where it needs to ground the spark will travel along the outside surface of the ceramic material under the electrode before jumping to the ground, ceramic may be an insulator yet electricity encounters lower resistance along it's surface than the surrounding air until it reaches the shortest route to the ground, so it will spark. Wall of text, sorry if anyone has fallen asleep attempting to read this. Hell of a first post though.