CVK Keihin conversion for old Zeddies

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CVK Keihin conversion for old Zeddies

Postby Gosling1 » Sun Apr 08, 2012 9:05 pm

I have been thinking about this conversion for a couple of years now - ever since I picked up that GPZ1000RX. This bike - and heaps of subsequent 4-cyl kwakkas from the mid-80's right through to now :shock: - use CVK Keihins of one type or another.

The CVK Keihin is a semi flat-slide carby. It gives heaps better response than the old slide-carb Mikuni's found on old zeds, and also the CV-style Mikuni's found on early-80's jap bikes like the Z1000J, GSX1100 etc. Even though these were a better style of constant-velocity carbie, they still used round slides.

I installed a set of 34mm CV Mikunis to Cherry back in 2001, to replace the standard 26mm slide carbs. Once the 34's were jetted up correctly - they worked really well. Great economy and you got some reasonable poke as well - 34mm is 34mm any way you look at it :lol:. CVK carbs are also cheap as chips at the wreckers - and far cheaper than any of the normal performance carbies you normally see on old 4-cyl jap bikes. Even a set of Mikuni smooth-bore carbs are up around $800 these days ! :shock: and if you want current FCR flatslides or CR's etc - well expect to spend well over a grand.

With Cherry currently undergoing a rebuild, I figure its as good as time as any, to sort out this conversion. I want some extra grunt with this bike - for reasons that will become apparent really quickly once the build is finished :lol: :twisted: - and in the box of goodies that came with the 1000RX - was a spare set of 36mm CVK's which have already been pulled completely apart.

I had a good look at these carbies today, compared to a normal set of 26mm Mikuni slide carbs from a Z1000 motor. These old-school slide carbs are physically similiar in most respects from 1972 through to 1980 for aussie-delivered bikes - so this conversion should be easy enough for any Z900 through to Z1000 or even to the later 1100's ( all the cylinder bore centres are the same for the air-cooled zeddies so the carbie spacings are all identical - even the smaller motors use the same bore centres....).

In a nutshell - the following specs were determined:

OEM 26/28mm slide carbs - bore centre #1 & #2, #3 & #4 - 75mm
36mm CVK Keihins - bore centre #1 & #2, #3 & #4 - also 75mm . This is a good thing ;)

However - the bore centre between the 2 inner carbs is different.

OEM 26/28mm slide carbs - bore centre #2 & #3 carbs - 96mm
36mm CVK Keihins - bore centre #2 & #3 carbs - 86mm.

This is due mainly to the later water-cooled motors having the cam-chain up the l/h side of the block and not in the centre.

Here are some photos which make it pretty clear:


CVK carbs in front, Mikuni slide carbs at rear
Image

Image

its easy to see how the #1 & #2 carbs on each set line up perfectly - and the slight difference in the centre spacing - 10mm - which puts the #3 & #4 carbs out of whack....

So the conversion really only needs 5 seperate parts changed:

Upper rear carbie bracket - lengthened 10mm
Lower front carbie bracket - lengthened 10mm
Choke actuating bracket - lengthened 10mm
T-piece junction for fuel feed between #3 & #4 carbs
Throttle actuating arm between #3 & #4 carbs extended 10mm


Here are the individual brackets that need to be modded:

Image

from top to bottom, that is the choke bracket, upper rear bracket & lower front bracket. All just mild steel, but all of varying thickness and profiles. Matching these for just a short 10mm extension will be a pain in the arse :lol:

The other 2 bits that will need to be sorted out are the fuel feed T piece and the actuating arm between #2 & #3.....here they are

T-piece
Image

actuating arm
Image


the T-piece could be dead easy. In the stock position, it sits almost flush inside each carbie body, with only the 'leg' of the T protruding upwards for the fuel line. To get a 10mm extension - it just needs to sit 5mm further out in each body. The ends of the 'T' are o-ringed to seal the fuel flow - on these carbs its a double o-ring at each end. Total length of each end is 21mm.....so moving it out 5mm on each side still leaves 16mm in the carby body. So I am just going to put new o-rings in, then fit the T-piece into each carby body like normal - and see how that goes. This could work - but if it doesn't well it just means getting some new T-pieces made up for the fuel junction that are 5mm longer on each end.

The throttle actuating arm is pretty simple - I just need to extend the arm 10mm out one side. This will ensure that the throttle movement is transferred between #2 & #3 correctly.

The whole conversion should be pretty straightforward as far as fitting to the motor is concerned - the width of the OEM slide carbs is 107mm front-to-back, the CVK carbs are only 100mm. The OD of the carbie spigot on the CVK carbs is 42mm - stock 34mm CV carbs like those on the Z1000J have an OD of 40mm - so I reckon these 36mm CVK's will squeeze into some stock Z1000J or GPz1100 inlet rubbers with just a tad of persuasion ;) . These manifold rubbers bolt straight onto a normal Zed motor. :kuda:

There will be no issues with the throttle cables either - the stock cable ends on any old zeddie will fit the CVK carbs easily enough. The only thing I may need to sort out is a choke cable up to the handlebars - the choke mechanism on the CVK carbies is a cable-operated jobbie - unlike the simple choke lever found on the old slide carbs. Small price to pay for better performance I think.....

I will have to source another set of CVK's though - while digging through the parts box tonight, I found out why these carbs had been pulled apart - some numpty has pulled the butterfly mechanism out of #3 carb, and fuxored the pivot in doing so :x.

Will be interesting to see how this all pans out.......

8)
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Re: CVK Keihin conversion for old Zeddies

Postby bonester » Sun Apr 08, 2012 9:40 pm

Wow. Great conversion...
2 X ZRX1200R 4 X ER6N, GT550, 1988 ZX-10, 4 X GPZ250R, 4 X GPZ900R and GPZ750R :) Yeah I like Kawasakis.
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Re: CVK Keihin conversion for old Zeddies

Postby Phil » Sun Apr 08, 2012 10:00 pm

Have you found a use for those ZX-9R carbs I sent you ;) ?
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Re: CVK Keihin conversion for old Zeddies

Postby Gosling1 » Sun Apr 08, 2012 10:14 pm

Phil wrote:....Have you found a use for those ZX-9R carbs I sent you ;) ?......


they will be fitted to the 1000RX - eventually ;) - when the motor gets a ZX10 head fitted to it...

Bones - can't wait to try this conversion out - I reckon it will give the old Z1000 motor a real kick in the arse !

8)
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Re: CVK Keihin conversion for old Zeddies

Postby the kid » Mon Apr 09, 2012 6:40 am

You don't have a sidecar sitting around do you Gos ?

Just thinking
Ummmm let me see
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Re: CVK Keihin conversion for old Zeddies

Postby Gosling1 » Mon Apr 09, 2012 1:22 pm

:lol: not on your life mate ......have been in a couple that was enough for me.... :shock:

Well I had a lash at modifying all the brackets this morning.......gasless Mig welder = much win !!

The most important bracket to get right - in terms of extended length - is the main front bracket. Get this right and then all the others just need to be matched up to the mounting holes on the carbie bodies....

Here is the first attempt - close but no cigar. It was about 1.6mm too short in overall length......basically the thickness of 2 hacksaw cuts :lol:

Image


When I lined up the carbie throats, you can see that #3 & #4 inlets are just a tad mis-aligned. It is crucial to get this fitting 100% correct - carbies can be enough of a pain in the arse to fit without 2 of the spigots being out by 1.5mm......

Image


So off came that bracket and a small 2mm extension was welded into place......with a very slight shave, this extra length got the job done :kuda: . If you look closely, you can see the slight casting ridge in both carbies on the top of the inlets. These now match up perfectly.....

Image

Image

Image


Here is a detail shot of the modified bracket - not pretty (yet) but 100% correct additional width.

Image


Next bracket to get modified is the rear upper bracket. This bracket has a dodgy U-shaped section, but I just used the same angle section to extend the width as used on the main front bracket.

Image

This bracket was then lined up over the mounting holes to see how close it was to accurate ..... :P

Image


Nice ! every hole lines up just right. Mounting screws can now be installed.

Image


Last bracket to get modified is the choke actuating arm. This is a lot thinner section than the other 2, so needed some different section steel bracket. Lucky the workbench is littered with crap, there was a small bracket of the right thickness sitting amongst the mess :lol:

Here is the modded choke actuating arm.

Image

Fitted up to the carbs - closed position

Image

and in the open position - all choke mechanisms working in synch.....

Image


really happy so far - all the major brackets now mean that these carbs will now bolt straight up to a z9/z1000 head as long as 1000J / GPz1100 inlet manifold rubbers have been fitted.

The 2 final mods I can't complete as yet - I need another full set of these carbs because the #2 carb on the spare set - is the one with the main actuating arm which transfers throttle movement from #2 to #3 carb - this is the fuxored arm. No point in extending the acvtuating section by 11mm on this arm because it won't be used. The fuel feed T-piece should work without any mods - I won't be able to test this out until I get another set of carbs, fit all the modded brackets and actually set the carbs up on a bike.

That should happen as soon as the motor gets fitted back into the frame. Not too far away..... ;)

8)
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Re: CVK Keihin conversion for old Zeddies

Postby MAXUMIS » Mon Apr 09, 2012 1:45 pm

Great work Gos,my uncle put a set of 87 gsxr1100 carbs on his katana motored gsx1100 and it made a massive improvement.He just had to get them jetted write and it made it a differant bike. 8)
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Re: CVK Keihin conversion for old Zeddies

Postby the kid » Tue Apr 10, 2012 7:28 am

Those green work benches are awesome
Ummmm let me see
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Re: CVK Keihin conversion for old Zeddies

Postby Gosling1 » Tue Apr 10, 2012 6:59 pm

MAXUMIS wrote:.....Great work Gos,my uncle put a set of 87 gsxr1100 carbs on his katana motored gsx1100 and it made a massive improvement.He just had to get them jetted write and it made it a differant bike. 8).....


I reckon these carbs will make a shitload of difference to an old Zed mate - time will tell.....


the kid wrote:....Those green work benches are awesome....


fully sick mate - good height for painting parts and cleaning - well they are for me, you would need a milk crate to stand on :lol:
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Re: CVK Keihin conversion for old Zeddies

Postby MAXUMIS » Tue Apr 10, 2012 7:46 pm

They will make a big differance!this is just a little "true" story why my uncle bought those carbs and more :lol: when i had my gpz1100 c2? the same as your green one he got his gsx1100 fe and we went into the middle of nasho and had some roll on's and i blew his arse to the weeds 10 to 12 bike lengths,he rode the bike straight home and striped it down and bought a shit load of goodys including the carbs and rd 2/350 head light to get rid of that little fairing ,anyhow put the carbs on and done the rest,went back out to the middle of nasho and i just beat him buy 2/3 bike lenghts(the carbs made a HUGE improvement)swaped bike and i blew him off on his own bike :oops: we went back out the next night and i removed the fairing off the old girl and FMD i beat him buy around 7/8 bike lenghts but i nearly riped my self off the bike when i pulled my head back up.Those were the day's ;)
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Re: CVK Keihin conversion for old Zeddies

Postby the kid » Tue Apr 10, 2012 8:08 pm

Gosling1 wrote:

the kid wrote:....Those green work benches are awesome....


fully sick mate - good height for painting parts and cleaning - well they are for me, you would need a milk crate to stand on :lol:


Height I can understand , but how do you get close enough to actually touch the lid ?

Just a question , not a judgement

:twisted:
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Re: CVK Keihin conversion for old Zeddies

Postby Gosling1 » Tue Apr 10, 2012 8:51 pm

:lol: only 4th Dimension waste in that bad boy. maybe a few tissues as well ? :oops:
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Re: CVK Keihin conversion for old Zeddies

Postby Gosling1 » Wed Dec 05, 2012 9:48 pm

Some more progress with this conversion has happened recently......picked up some 5mm ali plate pretty cheap and also a nice section of billet T6061 rod. Lucky to find it in 45mm OD as well......which just happens to be the same OD as the inlet stubs on a 1000RX motor.

Old mate up the road turned up the rod into some nice spigots, I cut out the flange plates from the ali plate - and this is what we ended up with :kuda:


First - get some nice 5mm aluminium plate - like this....

Image


then cut out the flange plates (just copies of the OEM inlet manifold flange shape)

Image


Take a nice piece of T6061 billet rod - like this.....

Image

and turn it on a lathe so it looks just like this....with the right taper to suit the OEM rubber manifolds...

Image
Image

Shape the flange plates and drill them out so they look a bit like this...

Image

then by the magic of JB weld :lol: slide the 2 parts together and leave overnight......and you end up with 4 of these....

Image
Image
Image


so there you have it, 4 nice inlet manifold stubs that will bolt up to any 1000/1100 kwakka head, allow the OEM 1000RX inlet rubbers to be fitted up......which then allows the fitting of the modified Keihin 36mm semi-flat slides seen earlier in this thread. The throttle cable fittings are basically the same as those on the early 900/1000 motor so I don't expect any problems with the cables.

Jetting will be interesting, but I don't think they will need too much changing - its still a 1000cc motor after all. May have to fiddle with the low-speed circuits probably.....

More to come once the carbs are fitted up and I kick the old girl in the guts.......stand by.

:kuda:
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Re: CVK Keihin conversion for old Zeddies

Postby the kid » Thu Dec 06, 2012 10:17 am

Nice 8)
Ummmm let me see
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Re: CVK Keihin conversion for old Zeddies

Postby Gosling1 » Sun Mar 23, 2014 11:06 am

Just had a massive win with this carbie conversion.......

The final 2 pieces of the puzzle were sorted out this morning. Pics to come..........but in a nutshell......

1. The small extension tab I needed to weld onto the throttle spindle arm has been completed. This is a 10mm extension welded onto the stock throttle actuating arm - it now engages with the throttle spindle on carbs 3 & 4. All throttle butterflies now work properly :)

and

2. The plastic fuel T-piece which sits between carbs 2 & 3 right in the middle. Because these carbs are now 10mm further apart - I couldn't use the stock plastic T-piece. Gave it a try though - but as expected, it leaked fuel straight away when tested on the bench. So - it was time for some ghetto mods :lol: . When I changed the throttle spacings on the 41mm FCR flatslides to suit the Gixxer motor in the Gronk, there were a couple of left-over plastic T-pieces.....same ID and OD as the stock T-piece for the RX carbies.....so far so good.

Luckily - the FCR T-pieces are about 20mm wider than RX t-piece. They both have 2 O-ring grooves machined into the end of each T, to stop fuel leaking out......

So I just took 10mm off the long end of one of the FCR T-pieces - used a battery drill as a lathe and had the cut-off end sitting out in the breeze spinning nicely :lol: - then very carefully cut in 2 grooves using the angle grinder ! It is fitted with a really thin 1mm cutting disc - so all I had to do was bring the spinning disc up to the spinning plastic piece and slowly use it to cut in an O-ring groove - well 2 of them actually, right next to each other at the end......

Fitted up the modified T-piece and bench-tested for leakage.................not a drop !! Really happy with this - it means all the mods to these carbies are now complete, and I can test them in the bike :kuda: :kuda:

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