greg bender
http://www.thisoldtractor.com/gtbender
The stock air box could have been designed better than it was. Although a little inconvenient from a maintenance perspective, the real problem is non-filtered air leaks. The rubber boot that connects each carburetor to the airbox deteriorates over time and does not create a tight seal, thus allowing dirt into the engine.
Greg Field provided these instructions to me:
I just silicone the boot to the box. Silicone it, weight the boot with something heavy enough to smoosh the boot's rim to the airbox, and leave the weight in place for 24 hour until the silicone is dry.
These boxes are [very difficult] to install if you don't do it right. The trick is to detach the left carb by undoing the three screws holding the manifold to the head. Put the box in place, worming the right boot spigot over the right carb's inlet. Then worm the left carb's intake into the boot, and tighten down the three manifold screws to affix the carb. Then "wiggle" everything to its best alignment and so there is minimal twisting and puckering of the rubber of the boot. Insert and tighten the three airbox screws. Tighten the hose clamps to the carbs. Also, you may want to mess with the jetting some. I found that 40 pilots and 140 mains worked better than the stock jets. Better gas mileage, too, and no fouled plugs.
I do not like k&ns because I do not believe they filter air very well. They do flow air very well and strain out the big stuff, though. The stock air filter is probly not much if any better at catching grit than the k&n individual elements or single element for the airbox would be. If you hold either up to the light, you can see right through. And the stock element doesn't even get oil to help catch stuff. Unfortunately, there really isn't a better option for the loops (a paper element for the stock box would be ideal), so I ran a k&n element in the stock airbox.
Why the box? It keeps the k&ns out of the sun, so they stay oily longer (really, they do not filter at all if not wet, and 80 percent of the individual pods I see on bikes are dry as a desert) and clean longer because dust and dirt settles on the box rather than the exposed filter. Also, it significantly reduces intake noise. This was important to me.
The airbox may also reduce performance on some bikes. On mine, it seems not to have, though I never did any dyno runs to confirm that. My bike acquired a reputation for going faster than most people really wanted to go, so I'm pretty sure the airbox wasn't hurting me much.
Greg Field's instructions were very helpful when I first installed the stock air box on my Ambassador. Here are a few additional notes from my experience: