Remote Airbox (& intake silencing) on the cheap

Well, I ride to work everyday and the sound of a screaming 2smoke can be hard to take that early in the morning.

Something needed to be done...

Having hunted high and low for a source of K&N filters locally and getting nothing for my troubles save the ol' crazyeye, I was havin a hard time replacing the stock air filter (tho that's a generous description to be sure). I wasn't particularly excited about the K&Ns anyway, although excellent hi-flow filters - they aren't well suited to all weather riding, playing in the mud, and they sure as heck weren't going to quiet the intake scream any.

I searched high and low for an air box. I dug around online, I also looked at mopeds & motorcycles, pocketbikes, generators, chainsaws - you name it and I was there with ruler and notebook in hand. Nothing fit. Not even close. I was growing irritated and a lil desperate, not a good thing when it comes to "fixing" my bike.

Poking round in one of the myriad piles of "other" while on a smoke break at work, to my complete surprise I found what appeared to be the perfect air box for my bike. Not an air box at all, it's an electrical connection box for some mysterious application - complete with a four terminal busbar inside. I gave the boss two dollars, took it home, ripped the busbar out, stuffed a foam filter inside, and made the following - the hole through the back was even the perfect size to lock the hose in place! Should you be interested, that's very obviously a small length of 2" OD vacuum cleaner hose (my shopvac is now less than it once was), a couple of cable ties, and I can dig up the part number for the busbox should anyone want to create a similar setup.



Tucked away, I don't hit it while pedaling;


I thought I would need to make this intake larger, but as it turns out it's fine. I still need drill a small drain port(s) in the lowest corner, but there's never been any water in it... ah, it's on the "to do" list lol



It may not be the prettiest thing in the world, those with sexy choppers prolly don't want the "utilitarian" style heh - but if you beat your bike like I do and wouldn't mind a lil less noise, you could give something like this setup a shot.

Impervious to my romping in the mud, indifferent to the rain - it's not restrictive to any significant degree and actually does a respectable job of reducing the intake noise. This was going to be just an experiment, I was going to make a nicer one should this prove effective, but it's been almost a hundred miles now. It's worked so well I've not bothered

Cuts it down quite a lot actually 2door, tho I've no real way to describe how much lol - it dampens the tone considerably, though obviously doesn't "silence" completely, it redirects the noise to under the seat and adds just a touch of "bassiness" (if you don't mind made-up words).

I suspect much of the quieting effect & change in tone is the ridged hose tbh - I wonder if I used a heaver hose like a radiator line (w/a perm 90 degree bend) if it would be even quieter? *shrug* I like this 'un, so that experiment will hafta wait a while

It's not gonna make you stealthy, but it does help


Oh and thanks fer cluing me in on the box's original application! I almost had it, remembered seein' em before - bdamned if I could remember lol

There was no perceivable effect on performance, although at first I was concerned about possible restriction (small inlet hole and foam filter). Yet my engine ran no differently and the plug remained the same color - I had expected a slight enrichment of the air/fuel mix but it didn't seem to happen.

The hose is a 2 inch OD shopvac hose (for the smaller 3 gallon variants) and in order to insure there were no leaks, I cut down the stock air filter screws and put them back to plug the holes, cut a 1 inch piece of inner tube and slipped it over the end of the hose, squeezed/stretched/argued the hose over the carb inlet and used the inner tube section as a cover for that junction. I then used a cable tie as a "hose clamp" to keep it all in place, but on this carb there was a small casting flash that I needed to grind flush (underneath the inlet and hard to see) before it would seat properly. The foam filter itself is a cut down Briggs & Stratton, the hole in the middle proved perfect for going over the hose inside the airbox (capped as to force the air through the filter);


Air Filter Element - 272235S
Used on 3.5 to 3.75 HP Classic™ and Sprint™ engines after 1992 and 4.0 HP Quattro™ engines.

The addition of a section of inner tube came later so it's not in the pic There was a tiny air leak with my first attempt, the tube fixed that right up.


edit: If you have a hard time finding the correct sized hose and/or don't wanna anger a "significant other" by brutalizing the vacuum cleaner - try your local tool supply store and see if they have sections of hose for dust collection, common for woodworking

I tried to get a part number for the motor terminal box, yet despite the fact we repair such electric motors where I work - apparently we don't/can't order replacements...

I find this difficult to believe as the one I have was new and unused, it must have come from somewhere lol I will continue my quest for a source of these terminal boxes on Monday, I only asked our repair tech and while hes a nice guy and all, hes also not the most... helpful sort.

But here's a pic showing the box's original function to help any that may be looking for one, as there's any number of "motor terminal boxes" and most aren't nearly as perfect for this;



Good luck in yer scroungin'

***none of the following was done for the intake silencing BTW, it was all due to the small frame I chose and the carb not fitting due to the seatpost and Dtube***

The carb is far more level than it appears in the pic... I was crooked at the time

It is just a bit offset, the top of carb is about 1/8" off center - a bit more than the throttle cable housing. It was that or drilling a hole in the frame

By rotating the angled bit of the intake manifold I have some adjustment in position, but this is at the price of angle. I also removed about 1/4" from the middle where I made the cut to pull the carb down and in away from the frame, as well as rotated it to clear the seatpost. I may bevel the cut to help straighten the carb, I haven't done that yet cause it would need to be welded and I don't have a spare in case I mess it up.

I cut this alloy manifold as a template for a properly welded one (preferably stainless), but I've been so busy riding it... I need to get a real carburetor and tbh this has held me up too, I figure it's probably a slightly different size and this is a tight fit

I do have a high rpm/WOT cutting out issue, but this is a new development and I've run the carb successfully at a steeper angle than I have it now. I figure a slightly canted carb could drain the bowl just a little sooner, but that still would be just a flow problem.

edit: I was wrong *blush* but problem solved here: http://motorbicycling.com/f4/engine-cuts-out-speed-aargh-11170.html#post107516

lol - I just "stole" the idea from the various dirtbikes I've had, most of 'em have airboxes up under the seat so ya don't suck water on a crossing. The "silencing" bit I learned from ultralights, those strung-out 2smokers are loud O.O

Thanks tho, I like it too


BTW - if ya do decide to make one, check yer plug color before and after. Mine didn't alter my air/fuel mix at all, but ya never know