Ninja EX500 carbs on an XS650?

I've managed to get both my stock carbed 650s dialed in for a pretty consistent 1100-1200 RPM hot idle speed. Yes, a small idle speed adjustment is sometimes needed between hot summer running and cooler spring or fall running, but it's just a minor tweak, maybe 1/4 turn at most on the idle speed screw either way. It does take some tinkering to get the speed just right, fast enough so it won't stall cold but not run too fast once hot, but it can be done. I have BS38s on one and BS34s on the other. Both idle nice.
 
We tend to think of flow as this smooth process but with the intake valve rapidly opening and closing it's more like a jack hammer of jerky air movement.

Regarding the air stream and fuel atomisation, this a a really interesting video about that. With super slowmotion to see the pulsing air stream, very interesting to watch! And carb related I guess haha.


Wow! I never really thought about how the air flow would be so stop and go, it happens so fast. But that video is amazing and really shows exactly how that works. Very cool! :thumbsup:
 
Made some modifications to the carb set-up. Made a remote idle screw so you can more easily reach it during riding. super easy mode, only requires a easy bracket to be made:

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The part number: 160210005 from kawasaki.

Also made a proto for a new choke/enricher set-up. Testing everything right now

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and a video showing the working:

 
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Im trying to dial in the idle part of these carbs. Im running JJJ needles, 138 MJ and a 40 PJ. Mix screws set a 3 turns. The bike is hard to start without choke. takes about 8 kicks. Warm it starts with no choke and one kick usually.

It seems to work great everywhere except idling. It idles slow, if i turn in the idle adjuster just 1/8 of a turn more, it will start to hold very high idles like 2500 RPM and wont come down. setting the idle adjuster with the engine warm it does idle around 1000, but misfires pretty often and sometimes dies. I would like to run a higher idle.

I tried leaning the mix screws to see if im running rich, but then it just dies at idle. Secondly i opened the mix screws to 4,25 turns and this seems to help.
My question, do i need to up the pilot jets to 42 and close down the mix screws a bit? dont want them to fall out.
A search in the topic does not show anyone running 42 PJ....

My motor is pretty stock at 650, stock cam, just UNI filters and semi open exhaust.

Edit: typo on the PJ size. Currently 40, upping to 42
 
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Im trying to dial in the idle part of these carbs. Im running JJJ needles, 138 MJ and a 40 PJ. Mix screws set a 3 turns. The bike is hard to start without choke. takes about 8 kicks. Warm it starts with no choke and one kick usually.

It seems to work great everywhere except idling. It idles slow, if i turn in the idle adjuster just 1/8 of a turn more, it will start to hold very high idles like 2500 RPM and wont come down. setting the idle adjuster with the engine warm it does idle around 1000, but misfires pretty often and sometimes dies. I would like to run a higher idle.

I tried leaning the mix screws to see if im running rich, but then it just dies at idle. Secondly i opened the mix screws to 4,25 turns and this seems to help.
My question, do i need to up the pilot jets to 40 and close down the mix screws a bit? dont want them to fall out.
A search in the topic does not show anyone running 40 PJ....

My motor is pretty stock at 650, stock cam, just UNI filters and semi open exhaust.
Okay see you say that you have a 40 pilot jet. But then you say do you need to up it to a 40 pilot jet? What pilot do you actually have?
 
I have a similar setup with uni filters and Sportster mufflers and I'm using a 38 pilot jet at about 2 and 3/4 to 3 and a quarter turns out.

Cuz if you already have a 40 pilot and it likes four plus turns out then I think you maybe need to clean your carbs some more or something.

But if you have a 38 and it likes over four turns out then yes you should try going to a 40 and start over at one and a half or two turns
 
This makes me want to make two points. They're both pretty critical.

1 needles are black magic a tiny change can make it go from running to not running.
I'm using stock noodles with one washer underneath them oh, I'm hoping to take it to a nearby dyno this summer but it seems to run awfully well.

2 I've said this before that everybody thinks that you just set your mixture screws to a certain number like two turns out or two and a half turns out, but you really need to set your mixture screws for the best warm idle that lets you get good cold starts and doesn't have any hesitation or hanging idle or dipping idle after revving. Also hopefully no or minimal backfiring.

Okay I know number two is a lot
Think of it like a musical instrument each cylinder and carburetor need to be tuned to whatever they like.
 
My bike is also a little hard to start when cold. I think that if it had the airbox it might be a little better but that might be a function of these carbs that they are a more modern efficient design than the original BS Mikuni carbs and might be a little stingy on fuel. I also have a suspicion that if I had retained my electric starter I wouldn't even have noticed it because it would crank 10 or 15 times in a couple seconds and then just fire.

Just like you Bjorn, I know the idle mixture is pretty close because when my back is warm it will restart with one kick.

It's not right that when you barely turn your idle speed screw in it jumps way up, you should have some pretty significant adjustment available in either direction before it starts to work off the main jet.
 
Well I was suspecting that bumping the idle adjustment screw just raised the butterfly open to much, running it on the pilot jet mainly. The slides don't open (took the filters of to see) so the main jet is not feeding.

I have zero popping in the exhaust when I close the throttle.

I also checked for air leakage around the intake boots with deo but found nothing. I could clean the carbs again but I did a full rebuild last fall. These are the first miles of the year.

I just ordered 42 PJ but it seems like it very big, looking at the setup I'm running. However I tried screwing the mix screws inward when warm. But it would affect the idle in a negative way. Stalling the bike.
 
I tried switching to a different needle size and my bike wouldn't even start. And it should be running totally off the idle circuit to start.
I know you clean your carbs last year but sometimes you have to clean them two or three times to get all of it
 
Dont forget the air. compressed air in the jet bores helps so much. Also make sure no vac leaks w/ the diaphragms!!
 
Yeah I sure used compressed air! How do the diaphragms affect idle? I was never able to let them rise slowly by holding a finger over the oval opening. But was told to test them by blowing air in that opening to rise them, which they do.
 
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Cleaned the carbs, checked every jet, used carb cleaner, used compressed air. Reassembled everything, tested the bike.


Result: no difference. Still the idle is either staying high (>2000rpm) mainly when I open de throttle stop. Or it's around 900. 1/16 of a turn can make that difference.

Tried various mix screw settings from 1 to 4, some minor differences but still the same cultprint.

Stepped up to bigger pilots 40 -> 42
Started at 1,5 turns on the mix. Same result. Tried 1, tried, 3 it's all the same. I just can't get it to idle between 900-2000.

Any ideas left to test/check ?
 
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