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Old 10-08-2015, 10:37 PM   #1
ncbrock
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Default Motorcycle carbs on a B21

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.





Last edited by ncbrock; 11-14-2015 at 09:27 PM..
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Old 10-08-2015, 10:39 PM   #2
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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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Old 10-08-2015, 11:13 PM   #3
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You're car is awesome. I love the ghetto-ness of it, and that it works. I won't need a fuel rail, the fuel pump will be able supply the carbs with enough fuel.

Here is where I got the blank from:
http://www.classicswede.co.uk/Inlet_..._10892996.aspx

Once I get my own manifold made, I could possibly make another.
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Old 10-08-2015, 11:22 PM   #4
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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.

Last edited by Hotdoggin; 10-08-2015 at 11:28 PM..
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Old 10-09-2015, 01:01 AM   #5
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Quote:
Originally Posted by ncbrock View Post
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.




Where did you get blank flange?
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Old 10-09-2015, 07:21 AM   #6
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http://www.classicswede.co.uk/Inlet_..._10892996.aspx

Nice to see where it ended up
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Old 10-09-2015, 10:09 AM   #7
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Do we get a mad scientist discount? Hehehe.
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Old 10-09-2015, 10:36 AM   #8
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It's actually pretty shocking how well those fit in there.
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Old 10-09-2015, 10:48 AM   #9
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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.
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Old 11-14-2015, 08:22 PM   #10
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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
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Old 11-16-2015, 06:44 PM   #11
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Neat setup. I can't wait to see how it turns out.
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Old 11-16-2015, 07:20 PM   #12
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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?
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Old 11-16-2015, 08:35 PM   #13
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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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Old 11-16-2015, 09:26 PM   #14
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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.
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Old 11-16-2015, 09:49 PM   #15
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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.
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Old 11-17-2015, 09:08 PM   #16
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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.
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Old 11-18-2015, 09:02 AM   #17
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Quote:
Originally Posted by Hotdoggin View Post
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
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.
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Old 11-18-2015, 10:47 AM   #18
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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.
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Old 11-18-2015, 11:03 AM   #19
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Good choice on the yamaha carbs, they sure do make good stuff. Seems like a fun project.
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Old 11-19-2015, 06:12 PM   #20
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Mock-up is done, time to TIG it up.
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Old 11-19-2015, 06:43 PM   #21
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Drooling. Take my money.
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Old 11-19-2015, 09:40 PM   #22
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Gonna tap in a few vacuum ports so there can still be brake assist and climate control bits?
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Old 11-20-2015, 01:16 PM   #23
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This is so cool!
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Old 11-20-2015, 07:16 PM   #24
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Gonna tap in a few vacuum ports so there can still be brake assist and climate control bits?
Yes. I'm probably going to tap each runner and run a vacuum manifold like I did on my old GTI. Much better brake assist than one runner.
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Old 11-20-2015, 07:36 PM   #25
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Oh yeah!
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