Just for the heck of it, I wanted to see what happened when I removed the airbox lid on my stock 87 250X. It loses power. Why?

 

Too much air. Not enough gas.

 

Well, what doesn't make sense to me is this: The most restrictive part of the air intake is the hole in the carb. The 2 openings from the outside air into the airbox are bigger than the hole in the carb so even with the lid on, the air that is available to the carb is more than the carb can take in. I mean, I know it is totally true that with the lid off, I lose power. But when I think about this logically, I can't come up with a good reason why.

If I go outside and suck as hard as I can on a straw, how will I possiby get more air than if I suck on that same straw that is connected to a 2" pipe? It's the straw that is the most restrictive part of the airflow into my lungs, right?

I'm just trying to make sense of this whole air/fuel thing.

 

It's not only lean but you lose velocity. The air coming through the holes is traveling at a greater speed then when you take the lid off since now there is no restriction. If you correct the jetting you'll gain back what you lost plus a little more.

 

I'll take the lid off of mine today and see how it acts.

 

Well I tried mine with the airbox lid off. It seemed to make a little less power and a lot more noise.

 

Yep. Same here.

 

It's lean. Jet it accordingly.

 

No, no no, sprayegdt. It's not about jetting or more power or modifying my bike. It's just about me understanding WHY it loses power. It just doesn't make sense that the available air to the carb is more than the carb can take in. Lid on or lid off. So, why does it lose power when the lid is off? Why does anything change?

 

Read my previous post. It's a lean condition AND you lose velocity of the incoming are. But if you jet accordingly you will overcome the condition.