Author Topic: Running a single carburetor conversion  (Read 2825 times)

dehanff

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Running a single carburetor conversion
« on: June 29, 2016, 04:05:51 PM »
I may be known as the idiot on this forum but this idiot need help again :P

As recent problems have shown up with my XZ550 carburettor that was missing an float, I decided screw it. This was an XZ400 that already had the mismatched XZ550 carburettor.

I built a makeshift intake manifold just out of piping to see if it  even able to idle. Low and behold, it did. I used my one carburettor of the XZ550 carburettor set and mounted it and had some idling rough revs etc. Leaked a whole lot of air etc.

The point is I need some pointers if anyone had done this before me? What size carburettor I would need and jets etc. just basically any comment basically because I'm running out of options and really want to drive my XZ400...

Regards, Dehan Ferreira
South Africa, Western Cape
 

Walt_M.

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Re: Running a single carburetor conversion
« Reply #1 on: June 29, 2016, 07:35:28 PM »
I'm not sure what your definition of idiot is but I must be one as well. My carbs got ruined by ethanol gas and redkote tank liner. I am in the process of adapting carbs from an FZR600. I have had it running on the front carb which is encouraging enough for me to continue. The carbs are relatively cheap and plentiful here in the US. I have a thread, '83 mods about it.  Not much there yet but I am still making progress. Good luck with yours.
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fret not

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Re: Running a single carburetor conversion
« Reply #2 on: June 30, 2016, 01:04:01 AM »
For a single carb to supply air and fuel to both cylinders I would think it should be about 40mm venturi (throat).  (my spell-check doesn't like the word 'venturi'.  Just thinking here, Harley Davidson uses a 40mm carb, as does the Kawasaki KLR650.  Those carbs are side draft though, not down draft.
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dehanff

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Re: Running a single carburetor conversion
« Reply #3 on: June 30, 2016, 05:42:46 PM »
What is the venturi on the XZ550 carburettors? Wondering if I use the working half of my XZ550 set if the venturi would be enough? Seeing that it is already for an 400CC engine nd not a 550CC one... Really no charts or some stuff around. :P Ill check your progress aswell thanks! Ant comments on how the intake manifold should look like?

fret not

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Re: Running a single carburetor conversion
« Reply #4 on: July 01, 2016, 01:08:39 AM »
I think most XZ550 carbs are 36mm throat.  Should be enough to make a 400cc motor operate on one of them, but probably at a reduced rate.
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dehanff

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Re: Running a single carburetor conversion
« Reply #5 on: July 01, 2016, 04:16:23 PM »
I just finished up making my new intake manifold, double to single. I used solderlene for the time being to check if it will hold up. I was busy using the heat solder but ran out of wire. Will let It dry overnight and report back shortly. Hoping it would atleast start.

Going to need to drill a hole in my tank for the return line from my carburettor, any advice on the location of the hole? Thinking bottom of the tank.

Regards, dehanfff

Walt_M.

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Re: Running a single carburetor conversion
« Reply #6 on: July 01, 2016, 05:32:16 PM »
I suggest that you not put the return line in the bottom of the tank. I also suggest that you rethink the single carburetor, unless you will be okay with never getting much above half throttle.
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dehanff

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Re: Running a single carburetor conversion
« Reply #7 on: July 02, 2016, 01:58:18 AM »
Wil look into the location of return pipe, at the moment its between a single carb and bike that won't run. So I'm just going with the option that will actually get the motorcycle running! Why would I not be able to get above half throttle? Carburetor limitations, jets or whatever?

Walt_M.

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Re: Running a single carburetor conversion
« Reply #8 on: July 02, 2016, 05:38:15 AM »
It is the carb size. Half the size, half the air into the engine=half throttle.
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ArrrGeee

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Re: Running a single carburetor conversion
« Reply #9 on: July 10, 2016, 12:04:05 AM »
I think I have to agree to disagree with you on this one Walt.
if he did build a decent manifold for a single 550 carb on a 400 ?
it should be fine assuming he was able to jet it anywhere near correctly.
because it didn't flow as much air he would lose definitely some top end.
how much would be determined by the size of the carb he picked.
I believe 82's use a 34mm and 83's a 36. either way, around town
and lets say under 50 mph it would be fine in fact might even be better than stock
because of the higher manifold vacuum.  this makes a bunch of assumptions of course
on the manifold construction and carb placement.

These bikes would run great on half the carbs because they are in fact over-carbed. i
n my opinion the reason was to try and get the horse power numbers up to improve sales.

my personal opinion on the vision is that while they were copying the weber design, they should've taken it further
and actually installed a single 2 barrel progressive carb in the same way many other carb manufacturers
have done.  low throttle openings get you excellent drivability around town and power when you ask for it.
as we know, it hurt them in the long run.


good luck with your project, I would suggest you try and put it back to stock if you can,
when they are set up right they really do run well.

-Ron

Ron_McCoy

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Re: Running a single carburetor conversion
« Reply #10 on: May 17, 2017, 01:53:15 PM »
For what it's worth, the 60s and 70s Triumph TR6 ran one carburetor that was the same size as the two on the Bonnevile. The performance difference was very small. There is also a Mikuni kit for Norton Commandos that changes from two 32 mm Amals to one 34 mm Mikuni. Again the performance difference is very small. Even though the Vision is a 70 degree v-twin, the cylinders do not draw air from the carburetors at the same time. The main effect would be a less efficient intake and loss of the nearly straight shot carburetor-intake port of the dual carburetor intake. Probably a loss at high rpm, but not that major.




pinholenz

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Re: Running a single carburetor conversion
« Reply #11 on: October 27, 2017, 03:42:51 PM »
Hi Dehan,

Where are you up to with your XZ? I missed the reason you were doing a single carb conversion with the 550 carb on the 400. Are 400 parts a problem in SA?
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