Ninja EX500 carbs on an XS650?

This thread has been a great read, guys--thanks for sharing your findings. Mrriggs, my hat's off to you again for your perseverance and ability.

Now here's a challenge. Vacuum carbs work best with a still air box, but the OE Yamaha units are considerably undersized (2 liters would be a lot better). Has anybody thought about designing a larger air box and making room for it (compact battery with smaller batt. box, moving electrical bits and increasing volume under the frame covers, etc.)?
 
I may have over done it a bit but here is my airbox solution: http://pjl.kotipolttoinen.com/random/WP_20130421_004.jpg Electronics are in the airbox with foam sock filters. The box sits under the seat: http://pjl.kotipolttoinen.com/random/xs650-2013/WP_20130430_010.jpg It took a few nights to get the box done but I like how it turned out. Performance is good. No hesitations or strange behavior. Rev's higher than I dare to run it.

The EX carbs are one cm shorter than the BS34's. My intake tubes might be a bit too long for optimal performance. :shrug:

Pekka
 
grizld1 said:
Vacuum carbs work best with a still air box,...
Click to expand...

Do ALL vacuum carbs work best with an air box, or just the vacuum carbs running a jet needle tapered to work with an air box?

I certainly don't have enough experience to answer that. This is the first time I have ever put a needle from an offroad mechanical slide carb into a vacuum slide carb. It's also the only time I've had a vacuum carb with such instant and linear throttle response. It feels like I'm running direct slide carbs, only better. I shifted to fifth doing about 20 MPH and whacked the throttle open; there was no miss or hesitation, it just pulled (surprisingly quickly).

A properly tuned air box would likely show gains in a dyno test but I have no complaints with the way it runs now.
 
On Road Stars, we have no trouble with ditching the factory airbox and going withva direct clamp on K&N RA66V or similar K&N. That's with a 40mm Mikuni CV. Some step up the size of the slide lift hole for better whack it open response, but I can't tell mine is lacking any.
 
Mrriggs, the needle doesn't have much to do with the advantage of a still air box for vacuum carbs (though it would have to do with the need to alter jetting in the change from an overly restrictive air box to freer-breathing pods). A vacuum carb needs a stable air pressure differential between the vacuum chamber above the diaphragm and atmosphere. When the lower chamber doesn't vent into a still air box, air currents moving across the vent port cause pressure fluctuations. Large volume pods can help, but for optimal results a still air box is needed. This is not to say that vacuum carbs can't be tuned to work acceptably with pod filters; but there's a difference between acceptable and optimal.

Nice work, pekka! The added intake length will give you more grunt down low and in the midrange, and since you're not hurting at high rpm's, you didn't overdo it there at all.
 
grizld1 said:
This is not to say that vacuum carbs can't be tuned to work acceptably with pod filters; but there's a difference between acceptable and optimal.
Click to expand...

My bike is now running acceptably. It starts easily, accelerates briskly, and runs smoothly down the road. There are no sputters or flat spots. It is running better than it ever has. I no longer have to think about it. When I'm on the road, the bike vanishes. It's just me and the road. There are no longer those damn carbs distracting me from the experience. To me, that is acceptable.

Is it running optimally? I don't know. Maybe if I ever get my bike to the track then I will find out. Until then I'm just going to enjoy the ride.
 
Perfect. You just cost me some cash! Any ideas where to best source the needle you are using? Alternatively, are you planning on comparing that needle with any other profiles made for the Keihins? I wonder if there is something out there that would work better with the spring.
 
A good source for genuine jets and needles is jetsrus.com . if you are looking for the pilot and main jets you can look them up by make and model. If you are going to order new needles like the ones mrriggs has put in you will have to look at the needles for the pwk28's.
 
I ordered needles from Jets-r-us once. They took several days to ship which leads me to suspect that they don't stock them but rather just order them from Sudco then turn around and ship them to you. If you order direct from Sudco then you will get them cheaper and faster. Sudco doesn't have an online store so you need to download the catalog, dig through it to find what you need, write down all the numbers then give them a call. It's not as convenient but you can save quite a bit if buying large quantities. For smaller jet orders I still use Jets-r-us. The added convenience is worth a couple bucks.
 
I messed around with extracting the heads from the N36N needles and it went very well.

Below you can see a N36N needle with a swedged on "nail head".
CVKneedle01.jpg


I clamped an old chunk of steel brake line in the vise.
CVKneedle02.jpg


Slid the needle into the pipe, then smaked it out of the head with a punch.
CVKneedle03.jpg


Head on a punch next to the headless needle. Notice the needle steps down where the head was. This means the head will need to be drilled out to fit the new needle.
CVKneedle04.jpg


I held the head in a drill chuck and drilled it by hand with a 7/64" drill. It's very soft aluminum so it only took a few twists of the wrist.
CVKneedle05.jpg


Comparing new head to the plastic donut from a BS34 needle.
CVKneedle06.jpg


There is a recess in the spring holder which the nail head fits into.
CVKneedle07.jpg


The plastic donut is too large to fit in the recess. This doesn't effect the needle position but does add a little more preload to the slide spring. I'm not sure how much, if any, this extra 0.1" of preload would effect the slide operation.
CVKneedle08.jpg


Just another note about installing the needles. Drop the needle into the slide then put in the spring holder and slide spring. Compress the spring with your finger then jiggle the needle up and down. A couple time when putting the needles in I noticed a lot of slop in the needle because the spring holder wasn't seated properly. If you push up on the needle [compressing the spring] then let go, it will snap into place and you should no longer feel any lash between the needle and spring holder.
 
mrriggs said:
My bike is now running acceptably. It starts easily, accelerates briskly, and runs smoothly down the road. There are no sputters or flat spots. It is running better than it ever has. I no longer have to think about it. When I'm on the road, the bike vanishes. It's just me and the road. There are no longer those damn carbs distracting me from the experience. To me, that is acceptable.

Is it running optimally? I don't know. Maybe if I ever get my bike to the track then I will find out. Until then I'm just going to enjoy the ride.
Click to expand...


So was all the R&D on the Mikes knock-off PWK's worth it.....ha ha...
If these can be bolted on & tuned with such little effort - I think they are a far better option & imagine 2nd hand ones might start to get snapped up by the xs crowd....I know I've had a look....good work everyone.
 
The photo explanation is wonderful. Thank you!

Now then, if I was to start from scratch, would this be an accurate shopping list:
-Set of Keihin CVK34 carbs from a Kawasaki EX500
-Carb holders for Mikuni BS34 carbs
-Keihin PWK needles (specifically which?)
-Either BS34 needle "doughnuts" or modified CVK "nail head"
-CVK pilot jets (what size range for tuning)?
-CVK main jets (what size range for tuning)?
 
hotdog said:
So was all the R&D on the Mikes knock-off PWK's worth it.....ha ha...
If these can be bolted on & tuned with such little effort - I think they are a far better option & imagine 2nd hand ones might start to get snapped up by the xs crowd....I know I've had a look....good work everyone.
Click to expand...

Ha ha... As bad as those PWK's were I will admit it was an excellent learning experience. The PWK's cost $600 and a year and a half of tuning to work properly, plus too much effort to keep them working. These CVK's only cost me $200 and were dialed in in two weeks. I haven't run them long enough to know how they will hold up but have no doubts that they will be trouble free. No matter how you figure it, the CVK's are the better way to go.
 
Firerunner said:
I think, perhaps I've found something: http://www.splatshop.co.uk/catalog/product/gallery/id/2000/image/3517/

Then again, perhaps not. If its rubbish, let me know, and I'll delete it in order to keep the thread tidy.
Click to expand...

Those are the ones, N427-46. The Sudco catalog has a chart that shows all the available sizes. http://www.sudco.com/CatalogJPG/059.jpg

I'm using the JJH needles which are right near the center of the chart. That's a good place to start. If you have any issues there are plenty of other needles in all directions to allow you to fine tune it.
 

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