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Evo Big Twins
Evolution Big Twin 1984 -1999

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Old 30-11-2007, 10:46 PM
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Air cleaner air flow

I know the standard round EVO air cleaner has restricted flow, but is there anything that can be done with it, like cutting three 1" dia. holes in the bottom face, by the air intake, or is it the filter element that is the limiting factor?

I don't really want to spend money on an aftermarket unit if I can modify the standard item. (No spare cash, and I can be "careful")
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Old 01-12-2007, 12:03 AM
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kiwidave kiwidave is offline
Club Member
Join Date: Dec 2002
Posts: 6,319
Re: Air cleaner air flow

the stock backing plate which allows the airflow is the limiting factor which becomes very clear when one is side by side with the Screaming Eagle version. The SE, frankly, has bigger holes in it!

Go ahead and give it the Swiss cheese drill treatment! Shade Tree Stuff is good!

Also, K&N make great claims for their actual filters vs. the OEM one, which needs far more regular cleaning. You clean the K&N one every 50,000 miles!
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Old 01-12-2007, 11:27 AM
grbrown grbrown is offline
Join Date: Oct 2007
Posts: 5,020
Re: Air cleaner air flow


I don't know what the later models look like, but on my 1990 model the plastic back-plate had a blanking plate that closed off one of the inlet holes. It was a simple matter to remove it, increasing the airflow into the box.

My inlet manifold also had a washer welded into it, reducing the diameter to about 28mm, or about 50 percent of the carb throat area! That also was easily removed, but required removing the carb and manifold to do. You will find a significant increase in induction noise!

If you make any such mods do fit a jet kit such as Dynojet (I have just fitted a Custom Chrome Recalibration Kit to one of our bikes, for 32) to rectify the mixture and to remove the low-end lean burn.
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Old 01-12-2007, 12:46 PM
Posts: n/a
Re: Air cleaner air flow

I'll have a nosey at the back plate, but otherwise it's out with the hole saw. I've already got a K&N fitted, canme with the bike.

I've gone back to the CV carb after using an SU for a while - couldn't get it to run quite right, so I thought I'd start again. Should be OK with a Dynojet kit in, but obviously I've got to flow more air!
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