Inside Scoop on the MoFlow

Review by Randy Twells Photos by Randy Twells & Randy Aron

I met Randy Aron of Cycle Visions not long ago, and he showed me this great air cleaner that he thought up, called the MoFlow. He said, “Let me put this on your bike, and you won’t believe how it improves performance!” I said, yeah sure, ok, I am soooo non-technical, I will have no clue what it’s doing or not doing.

First of all, I happen to ride a ’99 H-D Springer Softail (FXSTS) that also happens to have a Mikuni carburetor. Now the one thing I DO have an issue with is, even if I WERE to clean my bike regularly, it would still have this snotty drip coming out of the breather tube, dribbling gunk down onto the derby cover. And apparently I am not alone. Anyone know this one??

So when someone says they can do something that will improve performance, ie, make me ‘gofaster’, I figure all that will happen is, MORE drippy gunk coming out of the breather. OK. I brought my bike at the appointed time and Randy himself, the master of his Cycle Visions domain in Old Town San Diego, put ‘er up on the lift and started the installation. As promised, it only took about 15 minutes, and I could see that if you have the instructions and can hold a screwdriver and a wrench (do I qualify?) you can do this yourself. But I was busy shooting the photos so left the wrenching to Randy.

As he worked he explained things and I will pass along the info. Most air cleaners have a flat outer surface as well as a flat inner plate with a small aperture for the air to flow into the carb. But nothing is really in there forcibly directing the flow of air that is just baffling around and somehow eventually makes its way into the carb—until now—- until the MoFlow.

The MoFlow Air Cleaner has an outer surface that is shaped in a decreasing radius conical configuration. This shaped conical center of the air cleaner fits directly over the aperture for the carb, with a back plate (velocity stack) that is also shaped with a pronounced curved lip.

This velocity stack as well as the conical-center outer air cleaner surface are improvements over their ancestors, both flat plates that do nothing (NOTH-eeeeen!) to promote, direct, encourage or facilitate the flow of air into the carb. But this MoFlow acts like a black hole, smoothly and inevitably directing the air over all its curved ever-concentrically shaped surfaces, right down into the carb (or throttle body on fuel injected bikes) where it belongs, express delivery of air where needed.

I got some figures to back this up. Standard airflow on a typical Harley model is 325 cfm (cubic feet per minute). The same bike with the MoFlow installed will pull 450 cfm. This translates to about a 5% gain in horsepower. Like your bike is ‘wearing nothing at all’ to restrict that airflow.

To top it all off, the baseplate is attached to the breather blocks, drops oil straight down thru the velocity stack into the top of the carb/throttle body instead of into the side, essentially—- and is sealed at all points with o-rings. Soooo, it therefore ELIMINATES NOSEBLEED. Yes, no more gunky drip, every time you look down at your just-detailed bike, like I did as I pulled in to Cycle Visions for the install—- and I can assure you that I have no more nosebleed, ever since!! More Hp, no Gk (Gunk)!!

The really fun part though is, when I got on the freeway and just rode around, ohmygosh, my bike all of a sudden wanted to GO. I get on the throttle and, seriously, it’s like it slingshots out on a big rubber band. I did not have any preconceived input as to what to expect specifically, I wanted no bias, so I just let Randy put the thing on and then I thought well, we will see if I notice any difference and if so, what. Well that was it, I’m sorry Randy but you can’t have it back now…. No sluggish delay while the carb attempts to give the motor what it’s asking for. Immediate response and very smooth, also unlike previously. Just with this one change.

As for how it looks, there are several styles, a simple single-opening unit, a double with fluted shaping along the unit, a single with an iron cross, and a new triple-opening unit. All the hardware, fasteners and breather tube are hidden or internal, so everything looks clean and uncluttered. It also takes up an inch less space sideways, so it’s more comfortable riding with the MoFlow’s low profile, as I found on a full day’s ride.

The MoFlow outer cover starts out in the design process being shaped from a single piece of billet aluminum for the prototype, then that is used for the ridiculously expensive molding process. The production units are cast aluminum and chromed. I got the double-opening, and it fits the understated all-business look of my bike with the new drag bars and stripped clean of all the windshield/sissybar/luggage rack/saddlebags— all gone. Yes I learned to travel light….

The MoFlow has a re-usable (cleanable) pleated air filter and fits 1989-2007 Evo and Twin-Cam motors with CV, Delphi, S&S or Mikuni carbs. (You need the separate CV adapter for the Mikuni.) The MoFlow costs $299.99 and you can find out more at