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Motorcycle carbs on a B21

ncbrock

ncbrock

New member
Joined
Jun 18, 2012
Location
Raleigh, NC
I bought a $500 245 plagued with kjet issues so I decided to rip it out and go with motorcycle carburetors from a Yamaha. Also bought a blank intake flange and will be welding my own manifold. Once I get the manifold welded up it should fire right up, I will be running a bypass fuel regulator to get the ~3psi needed for the carbs.
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So. You interested in making me one of these manifolds? I own a car that has had similar done to it, but I have a single barrel carb off a Yamaha Virago 1100... My car was 150$.

https://www.youtube.com/watch?v=ePsA9a5yhXs

For a fuel pump, I'm running a mostly dead FI pump. Gives me about 5 psi. I'm dead serious, I've been pondering this for a long while waiting to buy my welder and do this myself... It works. My car starts up every single time, and even with the damn single barrel, it is very peppy. The B cam really likes this setup. What're you going to do for a "fuel rail?" I was planning on hard plumbing something, so the carbs still maintain gravity feed.

As you see, my car was done by a madman, pretty much as a proof of concept, but pretty badly. Plugged the manifold of the B21E with a block off plate, ground out a hole, shoved in some fence post, JB welded it in... I'd really much prefer to have what you're going for. :)

Where'd you get your manifold blank from?
 
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Yeah, Please consider it. We'll work out a price, and I'm real serious about it. I have since sort-of undid a lot of his ghetto-ness, but with some of my own. Looking forward to seeing what yours turns out like. How do you plan to mount the carbs to the manifold? Bolt on or boots, or what?

I can't wait to see how it turns out.
 
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ncbrock said:
I bought a $500 245 plagued with kjet issues so I decided to rip it out and go with motorcycle carburetors from a Yamaha R1. Also bought a blank intake flange and will be welding my own manifold. Once I get the manifold welded up it should fire right up, I will be running a bypass fuel regulator to get the ~3psi needed for the carbs.
7gU2B3Rh.png

8qNDc28h.png

LOUvkZ9h.png

jBwXU0oh.png

H19Wxpeh.png
Click to expand...

Where did you get blank flange?
 
The spacing may be a little slim, so the manifold may have to suck in toward the carb side, but they are pretty much made for it. From what I understand, they're pretty small for the cars, but can be jetted into efficiency. This is a good way around buying webers or dellortos, especially if you already have a bank of the carbs. I'm looking at carbs from an older GSXR1300r sitting on a wrecked bike at my local yard. The throttle response is great on these things. If you can feed them proper air (some sort of cool, fresh air,) they'll run like you couldn't believe. The single carb on my wagon does stuff the kjet wouldn't have allowed. The only tool I need to keep in it is a rubber mallet, in case the float sticks or something.
 
I got a little work done on the manifold. I've been busy with my e30s, but finally found a free weekend to start working on it. It's been really tricky, as I'm working on 3 planes here and trying to get the floats as level as possible. Also all this cutting has been done with an only angle grinder:rofl:
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Are you looking into a manifold that will mate all four together,or is it gonna be one cylinder intake per carb?
 
One per cylinder would be ideal. The way mine is setup, cyl 4 runs lean until a certain point.

I can't wait for this to be done so he can make my manifold for me. :)


Im anxious to get some proper fast revving carbs onto my car. What boots are those? They look fancy. Planning on supporting the bank of carbs from the bottom? I've already been looking into building a proper fuel rail, pressure gauge and all. The
 
One carb per cylinder. The boots are 5-ply reducers (1.875"-1.5") that I got from mandrel bending solutions. I'm not going to be supporting the carbs from the bottom, the piping I'm using is schedule 10 pipe (stuff people use for turbo manifolds) so it's plenty sturdy to support the carbs along with the 5-ply silicone.
 
Are they pretty stiff? I'm really excited to hear it rev, it's going to be quick. I wonder what kind of jetting is going to have to be done, hopefully it isn't terrible. I guess it'll all depend on manifold vacuum when it's all said and done.
 
Jetting will need to be dealt with. I'll see what the 2.0l vw guys are running, but I know they needed larger jets. The silicone boots are pretty stiff and could support the carbs by themselves, but the more I look at the the more I think you're right and might need a support underneath.
 
Hotdoggin said:
One per cylinder would be ideal. The way mine is setup, cyl 4 runs lean until a certain point.

I can't wait for this to be done so he can make my manifold for me. :)


Im anxious to get some proper fast revving carbs onto my car. What boots are those? They look fancy. Planning on supporting the bank of carbs from the bottom? I've already been looking into building a proper fuel rail, pressure gauge and all. The
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That's what is was getting at , that a manifold that joins together would slightly correct the lean cylinder. Like how the webers are 2&2.
 
Well, my setup is particularly janky. It's a bad representative of the idea at work. The lean cylinder will be eliminated with this setup anyways simply because of how direct it will be. No sharp turns. You can kind of employ some home AC design to increase your efficiency with these type manifolds. I'm interested to see how the low end turns out, I suspect it'll be weakish, then go ape**** around 2200...

You can use the old mounting location from the old manifold support bracket. Hell, if you cut and weld it, you can just use that mount.

The jetting won't be the main concern because mostly the main jet handles WOT, right? The Needles are what will be the pain to get correct, since they control the midrange.
 
Good choice on the yamaha carbs, they sure do make good stuff. Seems like a fun project.
 
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