[EmrysGsxr]

Alright, this question's a little stupid, but when I put everything I know together, they seem to conflict with each other. My question is. . . is leaner or richer going to give you more power out of your engine?
1st I've heard that leaner gives you more power. "Leaner is meaner" is what they say. Of course, you have higher exhaust gas temperatures and you're more prone to knocking, so you have to either A.)Retard the timing, or B.)Run higher octane. Or sometimes a combination of the both. Please correct me if I'm anywhere wrong with this.
But 2nd, if they make jet kits for carb bikes to pull more fuel into the engine, wouldn't that give you a richer condition? I don't have a jet kit on my bike right now, and I'm sure with the stock jets, I could run my engine rich as shit with the stock jets. .. so what would be the purpose of a jet kit? And of course you can't really modify how much air is getting into you engine too much without going forced induction. So, how does this jet kit give more power? Does it just smooth the a/f ratio through the rev band. .. ? That's all I can think about.
Let me hear what you guys think. Again, I know. . . stupid question, but I appreciate the feedback.

-Rob

 

[sportbike solutions]

It's not at all a stupid question, Rob.

The term commonly used to describe a 'perfect' air/fuel mixture is stoichiometric. In simple terms, a stochiometric air/fuel mixture is one that combines just the right amount of oxygen with just the right amount of fuel to completely combust the mixture. Too much of either results in a chemical imbalance... and thus a waste of either resource.

This 'perfect' mixture in gasoline engines is around 14.7:1, air/fuel, though this varies depending on any number of factors. But in general, this ratio allows for the most compete combustion (reaction), and therefore, for a given unit of mixture, release the most energy.

Now - on the subject of jetting. If you were already at the stochiometric A/F ratio, and you added in more fuel without any additional air, then you should, theoretically, make less power per unit of mixture. You'd have an excess of fuel, with not enough oxygen to react with it. However, when you jet to run richer, it's usually to balance out a change that was made that increased airflow (more available 02). Example: you switch to an aftermarket exhaust, the engine breathes better (takes in more 02), you add more fuel to bring the ratio back up to 14.7:1, and you now have more air and more fuel, both in the correct portions. that is going to make more power.

As far as getting more air into the engine... I think you're thinking in terms of volume alone. Sure, you can't dynamically alter the size of the cylinders, or the combustion chamber. So the volume of gas within the cylinder when it fires is always going to be the same. But the make-up of that gas is what makes the difference. A substantial portion of combustion byproducts don't make their way out the exhaust before the next intake cycle, no matter how efficient your engine is. By adding an aftermarket exhuast, opening up the intake, running a less restrictive filter, yada yada yada, you aim to expell more combustion byproducts, and make way for more clean air & fuel.