Project: "HonkyKong" 1979 KZ750 B Twin (brat-tracker-thingy)

As far as Im aware, as long as the intakes are the same length on either side, before the t..it shouldn't run lean..

Where did you find the pictures of the xs intake?
 
tron97 said:
As far as Im aware, as long as the intakes are the same length on either side, before the t..it shouldn't run lean..

Where did you find the pictures of the xs intake?
Google image search for "XS650 single carb" or KZ750 single carb", etc. There are crazier ones out there of guys doing 4-1 intake manifolds, etc. They make the work ahead of me look simple.
 
Yeah I still have it, I'll have to dig it out. Its going to get used on my build, but with the flanges welded on like I emailed you about. I never noticed a difference in temperature(possible lean condition) between either pipe but my manifold was fairly equal left to right. Thats the good thing about the KZ twin- the engine cradle is on either side of the engine with no backbone to interfere with a single carb set up. So for the most part you can run the carb straight back without having to bend it left or right. I understand about your electrical tray though.
 
Thanks, tobiism. I was going to ask if you might want to sell it for cheap, but since you'll be using it, nevermind. I think I'm gonna shoot for a left side exit anyway, to avoid the electrical box, keep the rear triangle opening clear, dodge the kicker arm and rear master cylinder, and to really show off the custom carb set up with THIS:

Yup, I'm committed to the idea now. I just picked this up off Craigslist for $20. This is actually off an S&S Super B carb, but I'm 99% sure those earlier S&S use the same bolt pattern as the 40mm Keihin CV. At least that's what my research on some Harley parts sites tell me.

I'll likely use a wire mesh screen & pantyhose 'filter' at the very minimum, and with it turned sideways, I won't get the rear wheel crud slung into it as badly as a rear facing carb might.

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If bolt pattern does fit, you will somehow have to make an opening for the bowl vent in the face of the carburetor. If you cover up that fourth hole with the velocity stack your bowl will airlock.
 
tobiism said:
If bolt pattern does fit, you will somehow have to make an opening for the bowl vent in the face of the carburetor. If you cover up that fourth hole with the velocity stack your bowl will airlock.
Thanks for that reminder. I think it sits on the same bolt circle as the others, so it should just vent to the outside air without issue (right?).

I may just have to hit it with a tiny round file near that 4th hole, if the flange totally blocks it.
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Been watching your build for a while now and I like everything you have done, except,,, here it comes, the single carb idea. With the amount of time and effort you will have into creating something that is inferior to dual carbs why not just throw on a set of new Mikuni VM34s and kn filters. For around $300 your done and they are so easy to jet and tune. The solid mount between the head and the carb is going to vibrate that single to death and the length of the intake will be a considerable power loss. I know there is something to be said about doing something unique, and it may work well, I just feel like you would see it more if it worked. I inquired about doing the same with my 79 bonneville and my engine guy would not consider it. (atombombcustom.com) Again I really like what you have done and enjoy reading the thread, good luck and I will keep watching.
 
Sorry but that is just incorrect. I have done what he is proposing and it works very well. I used the same carb on the same engine and had even better usable power than the stock carbs. Nothing shook apart and there was an increase in power by the seat of the pants dyno, not a decrease. Sure the dual mikuni vm's would be a nice addition, but 300 bucks is a lot of money for a bike that usually costs less than that.

Autotek said:
Been watching your build for a while now and I like everything you have done, except,,, here it comes, the single carb idea. With the amount of time and effort you will have into creating something that is inferior to dual carbs why not just throw on a set of new Mikuni VM34s and kn filters. For around $300 your done and they are so easy to jet and tune. The solid mount between the head and the carb is going to vibrate that single to death and the length of the intake will be a considerable power loss. I know there is something to be said about doing something unique, and it may work well, I just feel like you would see it more if it worked. I inquired about doing the same with my 79 bonneville and my engine guy would not consider it. (atombombcustom.com) Again I really like what you have done and enjoy reading the thread, good luck and I will keep watching.
 
tobiism said:
Sorry but that is just incorrect. I have done what he is proposing and it works very well. I used the same carb on the same engine and had even better usable power than the stock carbs. Nothing shook apart and there was an increase in power by the seat of the pants dyno, not a decrease. Sure the dual mikuni vm's would be a nice addition, but 300 bucks is a lot of money for a bike that usually costs less than that.

Agreed. less is more friends, less is more.
 
I'll be keeping my stock duals in case this doesn't work out, but I'd need to replace some broken / missing parts to get them fully operational, and from what I hear, jets for these are hard to come by. I have spare jets for the CV, and they are readily available at any H-D shop, as they used them for like 15 years on every H-D sold. I'll likely have less $ spent in materials to build this manifold than I would to repair the stock carbs.

This bike is never going to be a racer (insert Firestone slam here) so I'm ok with a few HP loss on the top end, as long as it runs smooth. Vibration? See previous pages. My 110rwhp H-D uses a single carb and vibrates WAY more than any parallel twin, and it works fine. In fact, it made 100rwhp (pre 45mm Mikuni swap) with the exact same carb as I'll be using here, and it has over TWICE the displacement as this 'little' 750, so although the less-direct intake manifold may hinder high rpm flow, I'm sure the single carb will not.

I look forward to making something unique. Even if its been done by countless others, its still a noticable variation from a stock bike.

I've got a friend building a hardtail out of a 1980-ish 4cyl KZ750, and I've yet to discourage him on the grounds that "performance will suffer". Of course it will, but that's not the point. I agree that different does not automatically equal cool, but I'll argue that in this case, it does.

tobiism, I may be hitting you up for baseline jetting and needle setting suggestions as I get closer to completion, if you don't mind. Note that I still have no functional wiring harness, so it may be a while.
 
Its been a while and I don't have any of it written down. I don't even have that carb anymore. But I know I had the needle had no shims under it and I had to go smaller on the idle jet(40 maybe?). I think the main was a 160.
 
So this was happenign this morning:

This is the trash pile, and it may get a little larger as I actually run the remaining wires. There are a handful of 4-way connections that will be reduced to a single connection in the final configuration, but for now I was just snipping away all things related to.....

- guage lights
- indicator lights
- turn signals
- oil pressure switch
- neutral switch
- that weird clutch lever anti-start switch (annoying. If I can't remember to find neutral or hold the clutch while thumbing the starter, I deserve to be bucked off my own bike when it lurches forward)


The remaining harness still kind of has a lot to it because (for now) I'm retaining....

- electric start
- a traditional key switch
- horn
- brake light (w/ activation switched at front and rear)
- high/low beam (will be simple toggle on headlight bucket)

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I also pulled the stock carbs and boots off to take a few measurements and play around with possible carb positions.

Rear-facing, mounted on same plane at the intake ports:
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Rear-facing, mounted below intake port plane:
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another view of the same:
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Left-facing, mounted at same plane as intake ports. Right exit hits the kicker pedal.
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I also did a rough knee-clearance check, for the side-exit option, and it looks like I'll be fine, even with a velocity stack protruding 2-1/2"" beyond the carb face.

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Cool man, I have heard that CV's don't respond very well to velocity stacks when the stack is in the turbulent air. Might be something to watch for, maybe a half round cover attached to the front so negative pressure doesn't develop across the face of the stack. I just pulled the manifold out of storage last night and looks like I can bring the carb about 1.5" closer to the head by getting rid of the rubber boots.
Now to see about installing that exhaust cam in the intake spot and retiming the engine!
 
tobiism said:
Cool man, I have heard that CV's don't respond very well to velocity stacks when the stack is in the turbulent air. Might be something to watch for, maybe a half round cover attached to the front so negative pressure doesn't develop across the face of the stack. I just pulled the manifold out of storage last night and looks like I can bring the carb about 1.5" closer to the head by getting rid of the rubber boots.
Now to see about installing that exhaust cam in the intake spot and retiming the engine!
I've heard that about stacks too, so I'll keep alternate 'filter' options in mind. Good luck re-working your own intake. The exhaust cam swap is on my future, to-do list, but I plan to get it running as-is first, in the hopes that you'll completely document your swap for the benefit of the rest of us KZ 750 twin owners. :)
 
I picked up some bits today. It's too wide with stock fitting lengths, so I need to trim the male/female interface areas to get to the approximately 5" center-to-center port spacing. I'll probably also this in the fore-aft axis, to keep the assembly compact.


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Interesting to use copper pipes. Have you heard of any problems with it? Are the inner & outer diameters the same? I haven't taken my carbs off yet to see.
 
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