Velocity stack/ham can

I'll be making some changes to my Commando when I get back to Mexico in Dec. The changes include: Smiths electronic tach/speedo, CNW front brake system (I have had their Brembo master Cylinder for years), the CNW rearset, and a set of Amal Premiers to replace the original (sleeved) Amals.

One thing I would like to do is put a pair of velocity stacks on the bike - really for looks BUT I hate the thought of no air filters. I was thinking about running the stacks into the OEM ham can but, of course, doing that essentially eliminates "the look" of the stacks since most of the VS will be inside the ham can.

Anybody have any thoughts about this? I am NOT doing this for any expected performance reasons; it is only for the appearance. I am not a fan of foam air filters but they would certainly be better than no air filter. Is there something that could fit on the end of the stacks? I am looking at these stacks: https://www.classicbritishspares.com/products/amal-type-long-velocity-stack-w-dome-screen https://www.classicbritishspares.com/products/amal-type-long-racing-velocity-stack-w-dome-screen Would these stacks fit between the carb and the plate that forms the back side of the air filter? I'm not at the bike so I can't go out to measure.

Again I am doing it for looks. I appreciate any thoughts, including those of the, "it's a stupid idea" type!

How many miles do you do?
I had a mate who ran his Commando for 18 years with no air filter, mostly but not exclusively on sealed roads. The only problem he had was earache from those predicting doom and gloom. Neither the doom nor the gloom eventuated although he had a few bikes so it was only 2 or 3 thousand miles a year.
My ES2 and 16h are both unfiltered, and the ES2 has done around 20k miles without yet complaining.

Mileage on my doesn't exceed 2-3k miles/year for the same reason - other bike available and ridden regularly.

Hi, it's allready a pain to fit the ham can , I can imagine the struggle to fit them plus the stack........but send pics when done, it's a good idea, it had been told somewhere here !

You could always try these shacks and I know you mentioned you don’t like foam, but K& N make sheet foam filters –by the sheet, and cut a suitable section out and fit over bellmouth to keep the dirt out held on by s/s wire or even a free post office rubber band as they keep dropping them around here

https://www.classicbritishspares.com/products/amal-type-long-velocity-stack-w-dome-screen

I will have to ignore the doom slayers who will wright in and say this method will restrict the engine breathing and make It asthmatic . . . .

Many Brit bikes rams without filters as new back in the day.

Vincent’s come to mind in particular, famed for achieving very high mileage’s and almost always without any filtration. Triumph Bonnevilles were filterless until the late 60s or early 70’s in UK spec.

So... whilst filters are obviously sensible, I would suggest that stacks are actually fine in reality, especially for a low mileage user.

I won’t get into the dirt into the engine discussion, I just know every time I clean my filter I’m amazed how much dirt and especially pollen gets washed out. There are two things that don’t usually come up, I think the filter helps capture water when riding in the rain. It also stops stray critters from getting into the carbs while the bike is sitting unused. Where I live every vehicle at one time or another has had its air cleaner eaten by some sort of vermin. Once leading to a fire in the air cleaner on a Jeep. So if you go that route you might want to get some kind of cover for the stacks when the bike is left unused.
Pete

Thanks guys - good point Pete! At the IOM this year I saw a bunch of vintage bikes with stacks that were covered when the bike was parked. A Bennelli Sei looked really cool with SIX of them! Anyway, stacks it is!! The longer ones in the links or the shorter ones? Also, I can't recall - is the OEM air filter back plate bolted or brazed/welded to the frame?

The VS's in the links have screens which would keep critters/large pieces out as would any sort of foam or other filter if I decided to use one. I suspect the screen also disrupts the airflow a bit. That would be a concern on a max performance engine but I can't imagine it would have any affect on a stock Norton 850.

As I said, this is for appearance though I wouldn't like it if it actually reduced performance over the stock ham can.

MexicoMike
I had the long machined Amal velocity stacks fitted successfully for about eight years, jetting similar to early 850 but number 3 slides and needle on notch 2.
They were the longer $$$$ ones in your link minus screens.
Comnoz did a flow test on the short ones with screens a while back and the flow was abysmal.
I bonded large K&N Oval filters directly to these, blending in the filter rubber for a smooth entry before final glue application.
Needed to run two tubes from the idle and needle jet openings in front of the carbs to new holes in each filter so all air goes through the K&N,s.
I also bonded the carb flanges to the velocity stacks as well as using the small grub screws. Synched carbs with vac gauges.

Made integral stacks for a kind of smoothbore conversion on my new Premiers fitted a couple of years ago but these sit inside a standard K&N R 0990 oval usually fitted to Commandos.

The stacks definitely were the snakes eyebrows and I,m looking at utilising them again but hidden inside a larger K&N RA 0270 oval.
I would never go without an air filter on a road bike, no matter what the old timers or race guys did.

Thanks Kiwi, great info!!

Going with these - will figure out some sort of filter setup. https://thebonnevilleshop.com/trium...32-billet-alloy-velocity-stacks-2-pn-928-076/

Triumph schmozzle type, ie that which Jack Shemans came up with for racing? Read that I think in the Trident book. Airflow not
disturbed by the flat area below the throat.

The ham can flows very well.

Velocity stacks with screens will cause a loss of power in comparison.

Open velocity stacks with no airbox may flow more or less then the ham can -depending on the wind and the turbulence in the area of the stack. Jim

Dutch said:

"Again I am doing it for looks."

Click to expand...

Understood, but there was also a desire to not loose any power.

Right - thanks Jim! I ordered a pair of 2 1/8" and a pair of 3 1/8" stacks (no screens). I'll fool around with the three alternatives - different stacks/ham can filter/OEM setup - and see what happens. I also have a selection of main jets from 260 down to 210. Since the bike is at 6400 feet, I can't imagine that even if the stacks actually make for more power/need more fuel, that the 260 wouldn't be sufficient. Currently the carbs have 240s ...or maybe they are 250s - I might have changed them when we moved from Mexico City - 7400 ft - to the current location at 6400; I can't recall. In any case, what's in there works well with the Concentrics/ham can. It's definitely EITHER 240s or 250s.

Of course, if I can tell there is a power loss with the stacks, I'll have a nice set of paperweights though since they are AL, they won't be much good for that!

I’ll be very surprised if you can tell the difference between those stacks Mike. I’ve played with them on the dyno and tend to see +/- 1-2 rwhp, maybe 3 tops. And a ‘normal’ person cannot feel 1-2 rwhp change, especially on th road.

A bigger risk is flat spots or other upset in the mid range. But I think you’ll be fine.

The main reason I ordered both lengths is that the longer one might actually work at a useful RPM range for the stock 850 motor. But I'm not sure the long ones will actually fit between the carbs and the plate that supports the ham can filter. So the shorter ones are for that possibility. As I said, it's for appearance as long as there is no perceived loss of power.

With a good following wind you will definitely feel a gain in performance!!! if you want to find out how, try this for gaining an extra kick from the engine from 60mph+ - fit two small plastic funnels to front of bike and run a house pipe from same to carb bellmouth and when you get to 60, twist the throttle on and off and feel the extra kick the engine produces-you will be surprised! DISCLAIMER!; No I will not be held responsible for you holing your piston if you have set the mixture too weak

Mike - for years and years I ran the "racing" stacks into my ham can. These are the second link in your first post in this thread. IMO they honestly added power and I suspect that they did so because their ID is the same as the Amals' carb bores - 32mm. Also, at wide open throttle, they extend your total (constant ID) intake tract length closer to CR Axtell's recommended 14"

The stacks which you first linked have a much larger ID because they screw onto the outside of the carb's inlet. Your second linked "racing stacks," because their ID matches that of the carb, cannot screw onto the outside of the carb's body; instead, they have a smaller bore and a step flange with three tiny set screws that screw into the outside of the carb bodies. When you tighten them you necessarily ruin the fine threads on the OD of the carb body's inlet. Worse, the screws inevitably loosen and then the stack falls off.

Another concern with the "racing" stacks is that they do not filter the idle circuit's air. The holes at the base of the carb's bore escape any filtration that might be applied to the stack's bore.

All that said, I would still be running them if my Amals hadn't worn out and been replaced with a set of Jim Schmidt's flat slide Keihin knock offs.

To answer your question about clearance to the back of the ham can - yes, with the "racing" longer stacks there was plenty of clearance. My bike is a '73 750 and clearance was maybe 3/8 to 1/2 inch at the lower edge, the closest part.

Sealing the stacks to the ham can's front plate was effective - put the rubber bellows on the inside of the front plate. Their notched flange goes into the plate's holes as normal except with the bellows pointing back, or inside; the other end of the bellows naturally seals up against the outside of the widening OD/end of the stack.

As you know, removing and replacing a ham can/filter can be a frustration; this setup is worse. Thankfully the Amals can be tuned in place - slides, needles, jets, all of it - without touching the ham can/filter assembly.

After the set up was proven, and because the three tiny set screws were a continuous problem, I epoxied each stack onto each carb body. The JB Weld epoxy also was used to fill the crack/gap where the stacks meet the inside of the carb's bell but fail to perfectly match it.

If you like, I can drag them out of their box and take pics for you.