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Thread: Velocity stacks for bike carbs

  1. #1
    SEi User turabaka's Avatar
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    Velocity stacks for bike carbs

    I was asking Cygnus about building or retrofitting a set of custom velocity stacks for my new Mikuni's, and we figured we'd just start posting up ideas outside of PM in an effort to get anyone interested involved.

    For those that don't know, I've been running 34mm quad CV carbs on my car for a little over a year now.





    While the current setup performs great, and gives excellent throttle response, they're just too small for the current motor work. I can feel them choking out at the top end.

    so, I've decided to bump up to 40mm Mikunis from a Yamaha R1. I figure these should be more than enough carb for all of my current motor work and some extra.

    However the problem is that the carb don't come with Velocity stacks like my old set, and the velocity stacks from the R1 are just really short and plastic.
    Here's what the Mikunis look like.



    What I'm hoping to do is find something that I can easily be removed. Similar to how the stock velocity stacks are installed. That way I can run pod filters on the street like I do currently, and just swap out to stacks whenever I go racing.

    ideas? suggestions? questions or comments?
    Last edited by turabaka; 03-22-2012 at 08:10 PM.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.



  2. #2

    cygnus x-1's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by turabaka View Post


    What I'm hoping to do is find something that I can easily be removed. Similar to how the stock velocity stacks are installed. That way I can run pod filters on the street like I do currently, and just swap out to stacks whenever I go racing.

    ideas? suggestions? questions or comments?

    So looks like the inlets are basically just open tube ends, no threaded holes for attaching flanges and such. Probably the easiest method would be to use rubber couplings with clamps like you did to attach the carbs to the manifold. The trick will be to find some stacks with exactly the right dimensions. What are the inner and outer diameters of the carb inlets? (the more precise you can measure these the better) Do the insides of the carb bores taper down at all or are they pretty much straight?

    Do you want to leave the stacks on all the time and put the filter pods over the stacks or do you want to take the stacks off as well and just put on the filters? Unless the pods have some sort of radius on the inlet it would be better to put the filters over the stacks. How much room do you have between the carb inlets and the firewall or other obstructions? The A20 is a fairly low revving engine so making the intake system as long as possible will help out the low and midrange torque.

    One possibility if you can't add much more length to the stacks is to make a sort of "donut", with a counterbore in the back that slips over the carb inlets. They could be permanently attached to the carbs with RTV or they could be slotted and clamped on with tube clamps. If the "donuts" had flat sides, some filter pods could be clamped on over the outside. Sort of like these but taller and with no holes:




    I'll whip up a quicky model for illustration if this looks like a possible route to take.


    C|

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    itzdave's Avatar
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    Re: Velocity stacks for bike carbs

    there are quite a few companies that custom make them for dirtbikes and stuff. i remember seeing them when i was trying to get foam clamp-on filters for my dcoes(with stacks). cant remember the names but i can try to find out what filters i had and check some sites...

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    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    I did find a company that makes aftermarket velocity stacks for the r1 carbs. They're roughly $300 though, and I'm just not willing to spend that on stacks. Especially when the carbs only cost me a whopping $67

    Here's the aftermarket option currently made. They're made by factory pro


    and here's what the stock stacks look like.


    There's a small notch on the end of the carb that you can't really see in the picture, and the stacks kind of clamp around that.

    I measured the carbs, and the outside diameter of the tube is 45.75mm.
    while the inside is roughly 41.90mm
    Also the inside of the carb bore is perfectly straight to my eye. It doesn't appear to taper at all.

    If it really comes to it, I guess I can run the stock stacks. I just don't think it would be that hard to cheaply make something similar to the factory pro style ones though.
    Last edited by turabaka; 03-24-2012 at 12:36 AM.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

  5. #5

    cygnus x-1's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by turabaka View Post
    I did find a company that makes aftermarket velocity stacks for the r1 carbs. They're roughly $300 though, and I'm just not willing to spend that on stacks. Especially when the carbs only cost me a whopping $67

    If you look around you can get the FactoryPro stacks for less, but still $200+. Take a look at this:

    http://www.ebay.com/itm/SINGLE-VELOC...eb78e8&vxp=mtr


    These are $10 each. The OD is very close to the OD on your carb inlets so you could use some short rubber couplings and clamps for attachment. The ID is bigger than your carb inlets so you would need to bevel the inlets with a dremel or even a round file, but that's no big deal.

    This is about the cheapest option you're going to find.


    C|

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    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    I like it.gonna go with those then, and post up pictures when they're all installed.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

  7. #7

    cygnus x-1's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by turabaka View Post
    I like it.gonna go with those then, and post up pictures when they're all installed.

    Excellent!

    One thing I forgot to point out is that they're nearly 4 inches long, so you might have to chop the bottoms off a bit if they don't fit. You're going to want at least 1.5 inches or so of space between the stack inlets and the firewall for proper air flow.

    So what do you have in mind for the filters? Will your old pod filters fit the new carbs?

    C|

  8. #8
    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    Do you think it would be better to run pod filters like I am currently, or to run the filter screens they make for those weber stacks?

    I was thinking maybe running these.

    http://www.ebay.com/itm/WEBER-45-DCO...sories&vxp=mtr
    Last edited by turabaka; 03-24-2012 at 02:28 PM.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

  9. #9

    cygnus x-1's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by turabaka View Post
    Do you think it would be better to run pod filters like I am currently, or to run the filter screens they make for those weber stacks?

    I was thinking maybe running these.

    http://www.ebay.com/itm/WEBER-45-DCO...sories&vxp=mtr

    The screens will restrict air flow less but the pods will filter out more particles. If the car is a race/show vehicle then the screens are probably fine. If you intend to drive it more often I would go with the pods.

    C|

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    Re: Velocity stacks for bike carbs

    I fail to see anything bad about the factory ones, other than them being plastic. Where do they fall in the affordability category? It seems like you might be able to buy stock ones for even less than those Weber stacks above.

    I do like those screen filters, but I don't think I'd run them on the street. I do like having a screen on my intake, even on the track, though. Our Challenge car made 3 autocross runs and had all sorts of stuff make it into the air box. Our engine probably ate some of it, too.

  11. #11
    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by Vanilla Sky View Post
    I fail to see anything bad about the factory ones, other than them being plastic. Where do they fall in the affordability category? It seems like you might be able to buy stock ones for even less than those Weber stacks above.

    I do like those screen filters, but I don't think I'd run them on the street. I do like having a screen on my intake, even on the track, though. Our Challenge car made 3 autocross runs and had all sorts of stuff make it into the air box. Our engine probably ate some of it, too.
    The stock ones are roughly the same price as the weber ones. I don't really see a problem with them either, I just kinda like the look of polished metal stacks on side draft carbs.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

  12. #12

    cygnus x-1's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by Vanilla Sky View Post
    I fail to see anything bad about the factory ones, other than them being plastic. Where do they fall in the affordability category? It seems like you might be able to buy stock ones for even less than those Weber stacks above.
    The factory stacks are not straight. It's hard to see in that picture but the opening is angled. You can find better pictures if you look around on ebay.



    Quote Originally Posted by Vanilla Sky View Post
    I do like those screen filters, but I don't think I'd run them on the street. I do like having a screen on my intake, even on the track, though. Our Challenge car made 3 autocross runs and had all sorts of stuff make it into the air box. Our engine probably ate some of it, too.
    This is why I'm making an air box for my ITBs. I like the idea of not restricting air flow but getting crap in the engine is worse. The screens are a good idea for race use.


    C|

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    Re: Velocity stacks for bike carbs

    Just a little update. Finally got around to installing the DCOE weber stacks onto my Mikunis. They required a little bit of dremel work to get rid of the slight lip the carbs have, and to give a nice smooth transition from the stack to the carb, but I think they turned out pretty well

    As you can see in the second picture there's a bit of a hole in the stack. I'm going to probably end up plugging it with some quicksteel and dremeling it nice and smooth. Aside from that though the stacks fit on nice and tight, and I'm not worried at all about them popping off.



    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

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    Re: Velocity stacks for bike carbs

    Looks great. The metal is very thin in that area, not much to grab onto. hope the quick steel doesn't come off and get ingested. I would just get some small rubber couplings to cover the gap, and a clamp to help squeeze it into the recessed grove, hopefully it wont leak.
    Last edited by A20A1; 05-19-2012 at 09:11 PM.
    - llia


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    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by A20A1 View Post
    Looks great. I hope the quick steel doesn't come off and get ingested. I would just get some small rubber couplings to cover the gap, and a clamp to help squeeze it into the recessed grove.
    sounds like a good plan actually. I might see what I can find.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

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    Re: Velocity stacks for bike carbs

    What about a wide rubber clamp that fits over the end? That would cover that hole and be more secure. The heat shrink hose clamps that Gates makes for big trucks work really well. They look pretty clean, too.



    Great minds do seem to think alike, eh?

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    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by Vanilla Sky View Post
    What about a wide rubber clamp that fits over the end? That would cover that hole and be more secure. The heat shrink hose clamps that Gates makes for big trucks work really well. They look pretty clean, too.



    Great minds do seem to think alike, eh?
    That's actually what I was just looking into. McMaster-Carr has some stuff that's looking promising.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

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    Re: Velocity stacks for bike carbs

    Sure beats the hell out of old school hose with worm clamps.

  19. #19
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by Vanilla Sky View Post
    Sure beats the hell out of old school hose with worm clamps.
    for sure. How big of a difference do you think it would make to get the heat shrink hose clamps versus just getting heat shrink tubing? Same difference in this instance?
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

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    Re: Velocity stacks for bike carbs

    The hose clamps will grip harder and likely look cleaner. On the other hand, the Gates clamps are $5 each. Every time you pull the stacks, it would cost you $20 to use them. I'm sure there's an eBay knockoff by now, though.

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    Re: Velocity stacks for bike carbs

    Wow never seen those before, looks perfect. Better then what I had in mind.

    Just in case you chose the rubber and it didn't seal 100% I was going to suggest a small metal peg be squished between the clamp and coupling right above the hole to force the rubber into the groove better.
    - llia


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    Re: Velocity stacks for bike carbs

    uni filter make oiled foam sock filters for dcoe/dhla style carbs.
    thats what i have for my itb set up

  23. #23
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by A20A1 View Post
    Wow never seen those before, looks perfect. Better then what I had in mind.

    Just in case you chose the rubber and it didn't seal 100% I was going to suggest a small metal peg be squished between the clamp and coupling right above the hole to force the rubber into the groove better.
    eh. I see what you're getting at, but it seems a little overcomplicated. Even if it leaks slightly it shouldn't make a noticeable difference since it's pre-throttle plates.
    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

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    SEi User turabaka's Avatar
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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by Hauntd ca3 View Post
    uni filter make oiled foam sock filters for dcoe/dhla style carbs.
    thats what i have for my itb set up
    These are the filters I ended up going with. they're just screens with a rubber boot made for the dcoe stacks.

    Lostforawhile:we have to pick on him he's CAH he spray painted himself into this corner with the accord.

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    Re: Velocity stacks for bike carbs

    Quote Originally Posted by turabaka View Post
    eh. I see what you're getting at, but it seems a little overcomplicated. Even if it leaks slightly it shouldn't make a noticeable difference since it's pre-throttle plates.
    True true.
    - llia


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