Air Box Modification Question

[skyjumper]

OK so I drilled out the drain hole and removed the diverter inside the air box on my Buddy 125. I understand this allows more air to the engine but what I don't understand is why you would have to re jet unless the air is restricted so much from the factory that is actually restricts the power of the engine in a big way. One would think a minor fuel mixture adjustment would be needed at most. Generally speaking it would make sense to build a product to its full potential and in this case allow as much air as possible through to the engine. Does PDO restrict the power of the engine for some reason by restricting the airflow?
I've worked on airplanes for years and an airplane runs fine without the air filter in place with no adjustment necessary. The buddy won't get off it's butt with just the air box cover removed i.e full airflow through the filter. To me this is just unharnessed power that needs to be released from the manufacture. Is there something I'm missing here?

[Lostmycage]

Simple: It comes down to efficiency.

They can't claim 100 mpg's with an open filter because if it were jetted for that, the fuel economy would be way down.

Also, they have to put in a certain amount of restriction so that it can be jetted to work in multiple altitudes. It's a machine that's bought mainly for efficiency; often very little thought is put into it for performance when a scooter is first bought.

Then there's the noise. It's a lot louder if you can hear the intake noise than it is with the box in place.

[bigbropgo]

There is something wrong if you are comparing the air flow of an airplane to a scooter. . Welcome to MB. air/fuel mixture is pretty on a small displacement motor tempermental. Every motor you ever work on or own can produce more power. But have you sacrificed reliability for it? I can be faster but have lower mpg and produce more heat. Scooters seem to be produced with a fair amount of power to reliability ratio. (They try anyway)

[skyjumper]

Efficiency....Of course! Thanks for that.

[skyjumper]

Thanks for the welcome.
I'm sure I'll have several more questions in the very near future. I have been scouring the forums here and will have parts on order soon for a transmission upgrade and 161 "big" bore cylinder kit.

[Kaos]

Yep, the above posters nailed it. Its all about efficiency. People buy scooters for fuel economy most often. Not for performance reasons. So they setup the bikes to get the best gas mileage they can, not the best power output.

[rajron]

I think one of the main reasons for scooter air box designs, appear to be restrictive, is for limiting intake noise something that becomes evident when modifying the box. So, the paid air flow scooter engineer not only has to deal with filtering, environmental control, and efficiency but the engineer has to make it quiet for the general public; a lot of compromises; hot rodders usually sacrifice something to squeeze that extra power, in the case of the air box modifications, getting noise for more flow efficiency.
Sometimes I wish my scooter was stock, becasue sometimes a smooth and quiet ride can be rewarding on a nice little cruise.

[Kaos]

I think one of the main reasons for scooter air box designs, appear to be restrictive, is for limiting intake noise something that becomes evident when modifying the box. So, the paid air flow scooter engineer not only has to deal with filtering, environmental control, and efficiency but the engineer has to make it quiet for the general public; a lot of compromises; hot rodders usually sacrifice something to squeeze that extra power, in the case of the air box modifications, getting noise for more flow efficiency.
Sometimes I wish my scooter was stock, becasue sometimes a smooth and quiet ride can be rewarding on a nice little cruise.

Yeah, thats got a lot to do with it as well. My scoot is LOUD. Both intake and exhaust. Too loud for a stock bike, but well within acceptable to me personally.

[JettaKnight]

Aside from the reasons stated, the airbox, intake tube and drain hole is to improve reliability by keep contaminants (dirt/water) from reaching the air filter.

Dust and bugs isn't a problem at 1000+ AGL so aircraft can run without an air filter. Also, aircraft aren't known for being quiet.

[iwabj]

oops

[michelle_7728]

Yep, the above posters nailed it. Its all about efficiency. People buy scooters for fuel economy most often. Not for performance reasons. So they setup the bikes to get the best gas mileage they can, not the best power output.

Efficiency--isn't that funny? You've nailed it of course, Kaos, that efficiency is the reason most people buy scooters. Funny, I say, because while you may save money on gas, owning a scooter is an expensive proposition! (helmets, gloves, jackets, pants, boots, top case, saddlebags, etc, etc). I know, there will be those that rightly say, that those are typically one time purchases and it will be cheaper down the road, but I'm not quite there yet. So "fun" (and lots of it!) is my main thing. Fun, and saving miles on my 2004 Corolla (just at 30K) so it will last me longer...cars are too darned expensive to have to replace.

[skyjumper]

Aside from the reasons stated, the airbox, intake tube and drain hole is to improve reliability by keep contaminants (dirt/water) from reaching the air filter.

Dust and bugs isn't a problem at 1000+ AGL so aircraft can run without an air filter. Also, aircraft aren't known for being quiet.

I didn't mean to compare an airplane and a scooter directly. I was just pointing out that an airplane, or even a car for that matter, runs the same with or without the air box cover on and was surprised to find the Buddy would barely run with the cover off.
It now has become obvious to me that the Buddy is designed to have the intake air restricted in order to keep fuel efficiency in check.

[Syd]

Yep, the above posters nailed it. Its all about efficiency. People buy scooters for fuel economy most often. Not for performance reasons. So they setup the bikes to get the best gas mileage they can, not the best power output.

Well, most people anyway!