Ninja EX500 carbs on an XS650?

Sooooo, after a great enduro run on the Yambler last weekend I told myself i was in no rush to swap my bs38 for the cvk, even though I've got all the parts in (minus the cable). The bs38 performed flawlessly but underwhelmingly, as usual. When I lost one of my vinyl vacuum barb covers on the way home I made up my mind to do the swap. The bs38 start up very easily but this motor is such a dog compared to my 650 triumph that's 12 years older. I'm thinking that it just isn't breathing properly.

A pair of 38mm carbs seem oversized for these intake ports and valves. My triumph breathes through a single 30mm and carburetes famously. I'm thinking that may be part of the reason why this motor suffers.
 
CDNTX650 said:
im still tossing around the idea of a single CVK34 Keihin (same carb as EX500, but came single on KLR250) on my XS.
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Would you cut the frame tube or redirect a single carb manifold out the side? I've been thinking if a single carb manifold and cutting the frame out if the way. There's something to the triumph u shaped manifold that boosts the low end torque....
 
scabber said:
They work really work well as a pair low end torque not a problem.
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Have you ridden a properly set up single carb triumph 650 twin? Torque is incredible for such a small displacement motor. Kills my XS, no comparison. It is a long stroke motor though, so it doesn't like to rev as high as the XS and I know that changes the torque characteristics.
 
Id do a joe wise guy offset one. I had one on a motor i built and sold with a single bs34. Ran great on the stand. I doubt the slight difference in runner length is anough to notice. Just do it for a fun project. I have my bs34s setup so well now though, that may take a while before i dive in.

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There's a breathe back balance through the triumph u shaped manifold. At low rpm the fuel charge has a ram effect into the open intake valve side from the closed side. Doesn't happen with any other parallel twin single carb manifold.
 
troopthrowback said:
Have you ridden a properly set up single carb triumph 650 twin?
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In addition to Honda, we were also a Triumph dealership. Yep, you could tell the difference on those single carb 650's. But, my properly set-up XS1B would blow their doors off, including the 750cc T-140's.

I have the feeling that carbs may not be your problem...
 
TwoManyXS1Bs said:
In addition to Honda, we were also a Triumph dealership. Yep, you could tell the difference on those single carb 650's. But, my properly set-up XS1B would blow their doors off, including the 750cc T-140's.



I have the feeling that carbs may not be your problem...
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You're probably right, though the 650s commonly destroyed the early 750s...

I'm likely not interested enough to tune these properly. Got my cvks, now it's on!
 
After reading this thread I was convinced to perform this upgrade. The BS34s that came on the bike were in bad shape so that helped make the decision easier as well. For background: the motor is a stock 1979 XS650 with TCI, stock head pipes, and Commando style mufflers.

I found a set of 2005 carbs on eBay for $75.00 that we're in great shape. I bought them along with 40 pilots, 138 mains, and PWK JJJ needles from Jets-R-Us. I cleaned up the carbs, installed the new jets and needles (third slot), and set the mixture screws and 2 turns out. I also notched the rear carb support to clear the frame member. I installed them onto the motor with some Uni Filters, gave it some fuel, and fired it off. After the carbs were primed, the motor fired off with no problem. After warm up and minor adjustments, the motor holds a nice low steady idle and has good throttle response. Still have a few minor things to work out on the throttle but not anything too big to overcome.

It is amazing the ease with which this upgrade can be done! Thanks again to everyone for doing the leg work and posting their results!
 
Cleaned my cvk pair today (off a 1999 ex500) and installed 38 pilot 138 main jets. Next is needles (need to pull my bs38s to get needle clips) and cables.

What to do with the brass breather nipples (blank them with vinyl "thread protectors" like the bs38 manifold vacuum barbs?)
 
So is one required to run a certain type of throttle cable for this push/pull arrangement? I'm going to pull a throttle and cable off a parts bike cm400 honda hawk I still have. Sounds like that may work. Thoughts?
 
I pulled the cm400 cables and they're pretty frozen. Soaking in some PB blaster and well see how it goes. Who's got a recommendation for cable fitment from an eBay source? Will a cable for an xt500 work, for instance?
 
I wanted to use the stock throttle pull and switch housing, so I used the stock XS650 throttle cable to use with the EX500 carb. All I did was rework the new carbs existing cable bracket to hold the XS650 throttle cable in place. A little crimping and a little boring (took all of 15 minutes). Easy and works great. There is no need to have a cable because the carbs return spring is pretty strong.
 
cbrrudy said:
I wanted to use the stock throttle pull and switch housing, so I used the stock XS650 throttle cable to use with the EX500 carb. All I did was rework the new carbs existing cable bracket to hold the XS650 throttle cable in place. A little crimping and a little boring (took all of 15 minutes). Easy and works great. There is no need to have a cable because the carbs return spring is pretty strong.
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:agree: Running the same stock throttle and switch housing. No need for the push cable.
 
Hey cbrrudy---How about some pics of the crimping and boring ??
 
Now yer talking! Looking at the cvk setup I was pretty impressed with the strength of the return spring myself. Now why on earth was it set up for a push pull throttle anyway? I'll get on mine next weekend, I pulled my electric starter today and still need to plug the hole it left. Apparently the freeze plugs I've got are a smidge too big... But that's for another thread...
 

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