Ninja EX500 carbs on an XS650?

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Pretty much every secondhand set will need a complete overhaul. Using a sonic bath on mine took out loads of crap on what were a very decent looking secondhand set and the float seats were scrap with new ones right next to rocking horse droppings on the shelf. Others may get luckier than me but I wouldn't take that bet.

 

[Its been a long time]

Yes, you are right about buying more than twenty year old second hand carburettors, without a doubt. Also the sellers now appear to be aware of XS650 owners buying them. The prices being asked are now unrealistic in my eyes.

So yes, what you have is a very realistic option providing they work correctly.

 

[5twins]

I started looking into these CVK carbs recently because I just acquired a Kawasaki W650 and it has very similar CVK carbs fitted. But, they're a bit more complex than these 500 carbs, with more electronic "fittings". So I thought maybe a simpler 500 set might be able to be swapped on. Also, the W650 carbs are jetted much leaner it seems, with only 118 mains, and they use two different needles, one slightly longer (leaner) than the other. Not sure what's up with that, lol. But, I planned on my typical mods (pods and pipes) so I know some re-jetting will be needed. I'm hoping it will just be minor, like our stock 650 carbs. But it's possible the W650 carbs "mirror" the '76-'77 XS650 BS38's. That particular carb set also had very small stock mains (#122.5) and requires more that just one or two sizes larger on the mains, more like 4 to 5.

I went on eBay and the 500 carb sets are quite expensive ($250-$300), so I don't think I'll be getting any soon, lol.

 

[Its been a long time]

I started looking into these CVK carbs recently because I just acquired a Kawasaki W650 and it has very similar CVK carbs fitted. But, they're a bit more complex than these 500 carbs, with more electronic "fittings". So I thought maybe a simpler 500 set might be able to be swapped on. Also, the W650 carbs are jetted much leaner it seems, with only 118 mains, and they use two different needles, one slightly longer (leaner) than the other. Not sure what's up with that, lol. But, I planned on my typical mods (pods and pipes) so I know some re-jetting will be needed. I'm hoping it will just be minor, like our stock 650 carbs. But it's possible the W650 carbs "mirror" the '76-'77 XS650 BS38's. That particular carb set also had very small stock mains (#122.5) and requires more that just one or two sizes larger on the mains, more like 4 to 5.

I went on eBay and the 500 carb sets are quite expensive ($250-$300), so I don't think I'll be getting any soon, lol.

Yes, sellers of used CVK34 carburettors have got very wise that other motorcycles are getting fitted with them. I have also seen the prices increase here in the UK too. To stupid levels.

For those prices it's almost the same as fitting a pair of VM34s. From memory they're often less than $140 each over there, new. I imagine there's W650s out there fitted with VM34.

 

[Wagner73]

My particular bike seems geared for a top speed around 0.5 C as near as I can figure so it's never going to pull arms from sockets when requested to do so. Setting off requires a most un-bike like slipping of the clutch.

Curious as to what sprockets you are running? My 78E has stock gearing (17-34) and 1st doesn't require a lot of clutch slipping (at least IMO), but neither does the gearing "feel" low-low either.

 

[Popshot]

Will have a look but will take a few days due to work.

 

[Wagner73]

I started looking into these CVK carbs recently because I just acquired a Kawasaki W650 and it has very similar CVK carbs fitted. But, they're a bit more complex than these 500 carbs, with more electronic "fittings".

Yes, I think these CVK's can have a number of electrical add-ons i.e. TPS, electric choke, and heat. Have a friend with a Triumph Bonneville America with CVK's and it has heat.

 

[Its been a long time]

Yes, I think these CVK's can have a number of electrical add-ons i.e. TPS, electric choke, and heat. Have a friend with a Triumph Bonneville America with CVK's and it has heat.

Indeed. Bonneville CVK36 has float bowl heating by electric heaters. And TPS unit.

Kawasaki CVK34 has engine cooling water carb heating. For XS650 the water tubes are removed.

 

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Got the new float valve seats. The extra length should be ok but will need to check further once on with the job. They are 0.25mm bigger in diameter which means I need to run a 10mm drill down the bore before setting them with thread locker. I should be able to have a good look into it on Friday.

These are for pwk 33 to 41 carbs.

https://a.aliexpress.com/_EJ1FuKS

 

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Curious as to what sprockets you are running? My 78E has stock gearing (17-34) and 1st doesn't require a lot of clutch slipping (at least IMO), but neither does the gearing "feel" low-low either.

32 on rear. Unknown front as that involves taking the exhausts off. I will have to schedule a sufficient strip to see as it desperately needs shorter gearing but will wait until I get a 16t front sprocket. I can't see it being that size or smaller though. Being a hardtail I have no desire to see the top side of 60mph.

My apologies for not updating this before now but in my desire to get a nominally 10mm od seat I failed to notice these new ones took a fatter needle. Correct ones for the seats are on the way and will report when I irrevocably drill the bodies for the new seats.

For the record I've now got a few miles on these Chinese carbs and still have no problems with them once warm though I do get some flames on the overrun from the open pipes whilst cold and still with a touch of choke. That possibly is the fault of the open pipes rather than the carbs. I would still rate these as a viable alternative to a secondhand set of Keihins.

 

[Wagner73]

32 on rear. Unknown front as that involves taking the exhausts off. I will have to schedule a sufficient strip to see as it desperately needs shorter gearing but will wait until I get a 16t front sprocket. I can't see it being that size or smaller though. Being a hardtail I have no desire to see the top side of 60mph.

Ahead of taking the exhausts, left side cover, et al off, you might try first swapping the rear for a 34. This will be noticable, and then you can decide about the front.

There is some info on this forum about smaller countershaft sprockets, but some advise against a particular minimum size (that I can't recall), due to the tight radius the chain must travel.

 

[Popshot]

A 32 may be on the rear as the distance between frame and chain is minute. Real Rizzla jobbie. I could splay it slightly and use a washer but I'd also need a longer chain.

 

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Got the old carbs drilled to 10mm for the new seats. The seats were a little tight so a modest bit of wiggle with the drill running at the bottom of the hole and the new seats have gone in very nicely. There's easily enough tab movement on the float to set the height. The tab needed bending about as much in the opposite direction as it was originally bent for the old seats. Tomorrow will see me swap to the old carbs and I'll then be able to see if it's leak free and also if that power difference I noticed was real or down to the fuel leaking out the back and getting sucked back in.

Seat sits 3.1mm proud.

Seat clears float.

 

[Its been a long time]

Well done. How are you going to decide on the correct float height?

Very interesting to see this since as far as I know, it's generally regarded as not possible to change those float needle valve seats.

 

[Popshot]

Float height settings should be unchanged since that is merely the level the fuel needs to be at to close the valve and it is measured to the closed valve in each case.

 

[Its been a long time]

Float height settings should be unchanged since that is merely the level the fuel needs to be at to close the valve and it is measured to the closed valve in each case.

OK, myself I would check with a clear plastic tube hooked up to the float bowl drain. Visual check of actual float bowl fuel level. Fortunately it's really easy to do on the CVKs.

But it's your carbs set and you've done well getting this far with them. Full kudos.

 

[Popshot]

Success. Carbs are leak free. A full run down.

Seats
https://www.aliexpress.com/item/1005010496791745.html
Needles
https://www.aliexpress.com/item/1005003907327479.html

Plenty of other sellers selling the same things. You can't reuse your std needles as they are too thin for these seats. A std shape 10mm drill goes in as far as the cast in lip you will see when you have the old seats out. A bit of good luck means the nose of the drill contacts bottom just as the cutting edge gets down to that lip. That is a perfect stop position for the drill. A bit of drill wiggle got me a hole perfectly suited to a tight fit tapping with a hammer. A bit of blue threadlock helps with the seal and is reasonably petrol resistant. Mine went in to 3.1mm proud of the body. The old seats come out with an M6 tap. Run it down and when it bottoms it will start to turn the seat. Twist and pull and it'll remove. The float height remains the same at 17mm.

Now to the other matter - Power

The difference I thought I'd noticed on a trip only around the block (I didn't want to go far with carbs leaking to a hot engine) is real, and now the carbs are actually working something like they should do that difference is very noticeable. The clone carbs are very smooth, more so than the current set up on the genuine set but that may just be a lack of being balanced. They are ultimately noticeably down on power produced. Whether that can be sorted with some different jetting I do not know. None of us are power freaks or we wouldn't have a 650 twin from the dark ages but that also means we can't afford to loose a lot either.
I'll have to eat some humble pie and change what I said earlier about the clone carbs being a good alternative now the issue of leaky old seats can be sorted. Sure, they work and are lovely and smooth, but you are going to have to play around with some bigger jets etc if you want that power back and you will. There is no guarantee that will do it either. In my own defence I never really had a good comparison against good real CVKs until now.