Bonneville America Forums Forums Technical Forums Performance Mods hole in bottom of airbox mod

Has anyone done this mod and NOT seen an improvment or even a loss of performance? I'm not talking about losses due to the need to rejet....i fully expect to do that if necassary. But i wanna know if anyone has seen a loss or no improvment even after rejetting for the mod.

I've done the mod and there is a noticeable gain in performance, the only drawbacks i found is that now i have a backfire on decel and cant seem to shake it but it is not as often since i put Thruxton needles in it the other day.

My only concern with this mod was getting water and road grime into the stock paper filter from the back wheel in the rain, i over come this by useing some foam for lawnmower filters but recently discovered that it didn't let enough air through to make a differance, while searching my garage for something else to use i spotted a mask that you use for when your sanding timber or spray painting , you know the little paper type with the elastic to hold it on ya head and guess what they are waterproof and let heaps of air through. Just cut it to shape and poke the dome part up into the air filter and the rest between the filter and bottom of the airbox, and "presto" a waterproof prefilter. Oh and cheap too

I took a new piece of 3-M Scothbrite pad traced the bottom of the filter cut it out and stuck it in. Seems to work really well.
ModelMaker

I drilled a 1 3/8' hole in my stock filter and in my airbox. All I noticed was that my right pipe started to turn gold sooner than usual, which tells me that it was too lean. I selected 1 3/8" because I had some chrome button plugs that size. I now have one of those in the bottom of my airbox..... '03 America with 130 mains, no snorkel(s), TBike pipes, and TBS needles.

Drilled a 1.25" hole in mine. Found a rubber grommet insert at True Value that fit and fabricated a screen from a fine strainer found at the dollar store that fits within the grommet (keeps the crawlers out).

Too cheap to dyno, but seat-of-pants performance increase noted. I bumped jets to 132 after mod due lean indicators which I guess is a good thing as the intent is to get more air-intake.

No regrets, I'd do it again and the whole can be easliy plugged.

Tom

Blackwind,

These dust masks do seem like paper, not sure of the brand i have as i don't have the packageing anymore, but they look like some sort of fiber and if you hold it like a cup under a tap it will fill up and not leak at all even when you touch it, Ive had mine on for quite a while now with no ill effects.

You gotta realize that the only difference (aside from water)between the stock top opening to the filter and the bottom that you drill is that the bottom can allow large particles like sand in. But that could only cause one problem......clogging of the filter ! because the particles that the bottom can allow in that won't come in thru the stock opening at the top are too big to get thru the filter anyway. So the only real concern, again aside from water, is clogging of the filter. And even that has not proved to be a problem for me. i started this thread a while ago and i did this mod already. So i don't see a problem even without adding a bottom screen of any type. Of course i said "aside from water" because that IS a concern if you ride in the rain. I don't so to me it's a non issue. But as far as other contaminents getting in thru the bottom, your only concern really is how often you have to clean the filter. And as i said that hasn't been an issue for me at all. Particles large enough to get in thru the bottom that can't get in thru the top are not only too large to get thru the filter, but for the most part they'll fall back down when the suction is released when you're at idle or when you stop the bike.

So i wouldn't worry about it. If you are worried about water then i have no answer for you other than not to do it.But for debris IMO it's a non issue.

as soon as i can i'm getting the freek.on top of the gains you'll get from more air to the carbs.just being able to get to the carbs is worth it.