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Carbs, other than CV

5K views 37 replies 7 participants last post by  Littlefeat69 
#1 ·
I have honda cm 400 t and was wondering if there were a different carb options to run pods other than the stock CV 22 A...are there carbs that I could buy do I didn't have to reset and alter stock carbs
 
#2 ·
see if you can find some Keihin CR22 smoothbore carbs.
 
#3 ·
Yes there are several options. Most that improve performance will also increase fuel consumption. Pods directly connected to a carburetor never was a great performance design, too much wind turbulence around them is the simplest way to explain it. Carburetors work best when they can draw from a large volume of reasonably still air and where the air travels in nice straight paths into and through the carburetor, fuel can't atomize as efficiently otherwise.

There is a hint right there 'smoothbore' carburetor, why is a smoothbore in a carburetor a good thing; for precisely what I was trying to say above, less swirly wind turbulence and no even negative air pressure around the carburetor intake is way better then what pods directly on the carburetor give you. That is basically an open carburetor with the addition of some air filtration. Ever heard of a velocity stack? It's a real thing, a good air intake has one.

Some carburetors you see when you are shopping are better suited to 2-stroke motors, try to stick with ones that are typically installed on 4-stroke bikes. :cool:
 
#4 ·
Go with vm30 mikuni's put a pair of 33's on a LTD 440 Bobber, It's a little ripper. I see them as low as 30 bucks new. have fun bolting them on because that's when the fun stops and the tuning begins. If you have never tuned a carb, just remember dual are twice the fun. CaTac recommended a great carb but I think putting Keihin's on a cm400 is a waist, you could buy another 400 lol
 
#7 · (Edited)
The CV carbs use engine vacuum to operate slides in addition to a butterfly valve that you operate by cable, (it's a pollution control / fuel saving device to make the motor run as lean as possible and represents the epitome of carburetor complexity which has thankfully been obsoleted by fuel injection)
the VM Mikuni type carbs on the other hand are strictly cable actuated, there is only 3 fuel circuits; low speed needle is a simple air screw, higher speed is controlled by a round slide that can have several different opening shapes, that in turn draws a long tapered needle that has 5 adjusting slots on it, the taper on the needle is adjustable by replacement. Choke is usually a fuel enrichment circuit that bypasses the slide throttle and dumps raw fuel into the intake port.
Fuel level to feed the main jet is controlled by a conventional float needle and seat.
The beauty of it is in its simplicity really, you can emergency clean and service them in the woods, with not much more then a swiss army knife and a thorn bush or cactus.
 
#9 ·
If you are buying the right carburetor it should fit the stock intake manifold adapter,
you don't get any extra mounting hardware when you buy carbs. You will likely have to devise a new throttle cable for it too, the one you have now likely has one cable to open and another to make sure it closes, the VM throttle will just be a straight pull cable connected to the slide inside the carburetor and the spring will be the only way to close it.
 
#11 ·
Not really a dumb question, one carb for 2 cylinders is an option, it's just not considered a performance option. One big carb would necessitate a unique 1 into 2 intake manifold. One carb simplifies tuning because there is nothing to balance, it might even be a little cheaper but it is certainly not a popular aftermarket modification.
 
#16 ·
Couple of points.
Honda deliberately made those carbs very difficult to modify, the '3 jet' models were EPA lean with weird transitions and work very badly without stock air box/filters
CV carbs allow people to ride bikes they really shouldn't be riding as they have very poor throttle control (the person not the carb) It doesn't matter where the throttle is opened the slide will only lift according to what the engine wants/needs
Don't trust anyone who says they have carbs corrctly set up for your bike unless they offer money back guarantee you won't need to swap out slides, needles, emulsion tubes (jetting is OK to need changes)
SUDCO are pretty worthless as everything is 'proprietory' and they just sell a 'stock' VM30 (stock for a 1970's two stroke MX bike) Virtually nothing inside them will work properly on a 400 four-stroke twin
 
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#17 ·
Mikuni VM can be fitted with either a bleed type or a primary type main jet depending on your application.
Piston port 2-stroke uses a primary jet, but for a 4-cycle or 2-stroke rotary valve application you install a bleed type jet instead.

If you took the Mikuni off an old 70's 2-stroker and put it on almost anything else, that part would need to be changed.



"CV carbs allow people to ride bikes they really shouldn't be riding as they have very poor throttle control (the person not the carb) It doesn't matter where the throttle is opened the slide will only lift according to what the engine wants/needs"
That is the basis for the fuel conservation and reduction of exhaust emissions, they took away the operators ability to ham-fist the throttle.
 
#18 ·
I know. I haven't seen any of the VM range for sale with emulsion tubes though, they all come with primary bleed. The ones I fitted to my XS 650 had a pair of emulsion tubes I machined to get various things working right.Emulsion tube and primary choke also use different pitch main jets which arte not interchangeable (without a big screwdriver)
 
#21 ·
I'm beginning to think I just need to keep stock carbs, buy a air box..have a battery box and used fuse panel with electronics attached..use wiring harness and redu the area he cut out...at least I got the time..not necessarily the knowledge View attachment 103671
What on earth is that piece of rusty metal that has been Horribly melted onto your frame tubes :unsure:
... don't learn to weld things onto a motorcycle frame if they can be bolted to the frame. That weld has so little penetration it wouldn't hold anything, the attempt did more damage then good. Is it a battery box? The battery box is ideally rubber mounted to begin with.

and by the way, you couldn't fit a single carb on that if you tried, the pressed metal frame member is completely in the way.
 
#25 ·
lol look at that, zero penetration, he must have had the welder voltage set way too low, held the rod at the wrong angle or he was using altogether the wrong welding rod and he probably attached his welder grounding cable to the scrap metal instead of the frame too. People like that should just use hot melt glue, it would yield far better results.
 
#26 ·
Thanks. I will try that next time I try to weld. :unsure: Even my worst welds have penetration. They just end up looking like bird poop. That was really bad though.

Good news is that it was easy to undo. Where should the battery box be on that bike and is he missing any brackets that he needs to fit the airbox?
 
#27 ·


Right side up to start with if it is a lead acid battery,
sealed or not you are not suppose to lay them down on there side as some have done before him.
If it is a dry cell batter LiPo or whatever then you can carry them at any angle.

The OEM brackets are just thin metal. there is no need to use metal that is thicker then the frame and things like that should be removable, that's why Honda bolts the box in place and locate tabs onto the frame where required. Second time around bike likely had the tabs all ground off by the previous owner in search of that stupid open triangle look nonsense.

Lead acid battery is a relatively heavy component, manufactures tend to keep heavy items central to the bike mass and the weight low as possible. Honda probably located the battery behind and tight to the right side panel for clearance reasons.
 
#28 ·
Returning bike to more or less stock would probably be a smart move as it isn't particularly 'desirable' and to anyone else will never be worth the time and effort you put into it (I have a lot of experience building bikes for me, most of which I still have or sold at a ridiculous loss)
 
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