Air Box Theory

[Pep]

What happened:
When building the modified Ace 90 (Ace frame with a reeded 94 engine) - space was tight, so I put a K&N filter on the bike. Tuned the carb, runs great, no complaints.
Extending this (faulty?) logic to my stock Ace 90, I decided to throw a K&N on that bike. Idled fine and all, but rode like I either put huge jets in or was using a filthy air filter - no power, boggy as heck. I put the original air can back on, ran beautifully. And here I thought an open filter like that would give it more air, more power…
This led me to read up on air boxes in two strokes…Poisson’s stagnation principles, air resonance theory, etc.
However, it seems to me that much of this air box development came in later two-strokes (late seventies, eighties, to present).
*So my first question is: were early two stroke air boxes simply a means to protect the filter from water, gravel, road kill, etc - or were designers thinking in terms of air flow and positive/negative pressure effects on the carb?
Based on the stock Ace 90 experiment, the engine seems happier drawing from a pocket (albeit small) of air, rather than an “open” system.
Practically speaking, I’m wondering if I’m doing that 94 engine a disservice by having an open filter on it. Creating a box or even using an Ace air can in that tight space is going to be a struggle, but worth it if there’s untapped reserves or unforeseen consequences coming.
I’m tossing these musings out to all you really smart/experienced folk, hoping for some guidance.
One last thought I have is that this may be more a matter of surface area - the stock Ace filter is larger than the K&N that went on the stock 90 - perhaps the air box reservoir idea is just a red herring, and a larger open filter would perform better.
Hope this doesn’t give anyone a headache,
Laurie

[Bullfrog]

While I can't see the filter you installed . . . my guess is that your last sentence is on target. A LOT of "sock" air filters get installed on old two-strokes because they are easy to find, purchase and install . . . and they are just too dang small to work well. If the air filter is too small, and the engine has to "suck hard" to pull air through it (not the way things really work - but descriptive) . . . the engine will find it hard to get air, but it will "draw" fuel through the jets with it's "suck" power and presto-change, you have a rich condition. This situation may be what you have going.

Ed