Ninja EX500 carbs on an XS650?

Ive not touched the old girl for weeks , it just wont stop raining...:banghead:
New baby due in a couplve weeks so I cant see myself being able to fiddle with the carbs for a few months:shrug:
 
I decided to try out the EX500 carbs on my bike. The carbs I got were off of an '04 EX500. They had 35 pilots, 130 mains and N36N needles. I had enough sticky throttle issues with the PWKs to last a lifetime so I wanted to take advantage of the push-pull throttle. I got a used throttle and cables from an '05 CRF250. I also bought a new set of UNI filters since my old ones wouldn't fit the new carbs. All that came out to about $100 then I spent another $100 on jets.

Installation was just as easy as the others described. Grind a notch in the bracket to clear the backbone, then slide them into the BS34 carb holders. The CRF250 cables aren't a perfect fit to these carbs. With the adjusters all the way out, there is more freeplay than I care for. I'll go back and shorten the cables when I get a chance.

Based on what others have written, I started with 38 pilots, 142 mains, and two shims under the needles. It started right up, idles well and runs beautifully down the road. WOT feels really good but if I pin it while cruising there is a little hesitation as the RPMs climb. All-in-all, I am blown away at how well these carbs work with so little effort put into them.

Thank you ippytattoo and others for sharing your experience with these carbs.
 
Thanks for the write up. Going to get the beast up here in Maine the weekend of the 15th and dive in on it. Seriously considering these carbs. My EX always fueled very well.
 
Thanks for the write up. Going to get the beast up here in Maine the weekend of the 15th and dive in on it. Seriously considering these carbs. My EX always fueled very well.

Where are you guys running the enrichener cable to? It's originally left grip mounted on the EX, but you have to use that switch housing for it so it has the channel for the lever. Didn't know if you were coming off the side with a Mikuni style cable or what.
 
I've just been pushing it from the right side with my finger. Now that I know these carbs are going to work well, I will spend some more time on the small details like the choke actuator.
 
I decided to try out the EX500 carbs on my bike.

Hello MrRiggs,

When you say 'my bike' do you mean your 're-phase'? I ask because, having no practical experience of this mod, I wonder how or if your settings are skewed as a result of it and how your results compare to a standard engine that I think we other posters are running?

In my case (an '81 SH) I've had 12mm spacers made up to fit between the head and carbs to get the carbs to fit on to the airbox of a standard engine but with no exhaust cross-over pipe. I'm retaining the airbox to prevent slide flutter, I hope. I also have a set of 1 1/2 inch dia downpipes to fit to the shorty reverse cone megas but I have a feeling that the downpipes may ruin what low down torque I have so I'm sticking with the standard pipes while I get it running on these carbs.

Later,

Ian
 
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I don't know exactly what MrRiggs is running these on but I was running these on a '81 666cc rephase with pods and open exhaust with the jets and shims as in my build thread and was just about to put them back in on a 750cc rephase. In all reality I doubt the rephase or even going to a 750cc would make a whole lot of difference to these carbs. Hope the info helps. With your setup the jetting maybe a little bit different due to you using the stock air box and exhaust. My guess is that it may work ok with the baseline we have come up with or you may need to tweak it a little but you shouldn't have to reinvent the wheel. My suggestion would be to get a couple different mains and pilots. I was actually trying to tune these a little more and was at a 40 pilot, mixture screw at 1 turn, 150 main and 1 shim on needle. I didn't get to ride it much to check plugs or fuel milage but the performance was there. Clean and crisp from idle to about 7000 rpm and at various throttle positions and cruising speeds.
 
'My bike' right now has a 360° motor in it, I pulled out the re-phase a couple months ago. I only swapped bottom ends, using the same pistons, jugs, head, carbs and exhaust as the re-phase motor. Changing firing order alone made no difference to the jetting.
 
Ippy, Sorry, man, I will have read that yours is a rephase in your 'build' thread but I'd forgotten.

mrriggs, Thanks, that's good to know. Have you got rid of the hesitation or are you content for now?
 
mrriggs, Thanks, that's good to know. Have you got rid of the hesitation or are you content for now?

I haven't messed with them much yet. I added a third shim to each needle and the hesitation seems worse. Next step is to go the other way and try removing shims.

Under normal riding conditions these carbs perform very well. The only time I experience a hesitation is when I goose the throttle without shifting down. The same thing that happens with direct slide carbs. It's really not that big of a deal but since these are constant velocity carbs it should be possible to tune that out.

Right off the bat these carbs worked better than I could ever get the stock BS38s to work. They are also more streetable and have better top end than the PWKs. I am totally sold on these carbs.
 
Hi all, read this thread with interest, thanks very much. I have just picked up a set of GPZ500 carbs here in the UK but am a bit confused as they seem to have so many hose connectors and wondered if someone could enlighten me.

At the top of the carbs at the front where they mount into the engine there are one on each carb which seem to be something to do with the choke mechanism - should they just be blanked off? Then at the bottom of the carbs there are plastic connectors - are these just the overflow. Then of course there is the fuel hose connector and what seems to be another overflow. I have posted a couple of pics - any help appreciated.

Cheers, Paul
 

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In your first pic what you have marked as "overflow" is actually an atmoshpheric vent and the 2 that you have marked as "Blank these off" are vaccumn ports (work great for syncing carbs with a manometer). In your second pic what you have marked as "fuel in" is indeed your fuel inlet but as far as the one that you are questioning being an overflow I am not sure. your best bet may be to find a plumbing diagram for the GPZ500 and see what it shows. I can tell you that on the US spec EX500 carbs I used there was not that hose in the second pic. Hope that helps.
 
I do not think that you have to block them. Just pull the brass pipes off the carb body.

I just cleaned my cabs today. Now I need to buy some new jets.

Pekka
 
I do not think that you have to block them. Just pull the brass pipes off the carb body.

I just cleaned my cabs today. Now I need to buy some new jets.

Pekka

You can yank the pipes and fill the port with epoxy. I forgot about the heated bowls. I only had the carbs off my EX500 once. They never needed anything.
 
I had a major breakthrough today. After trying more shims and less shims, I determined that these needles are just wrong for this setup. I wanted to try a straight taper needle but had trouble deciphering the needle code to find a compatible replacement.

The Sudco catalog gave some info for converting OEM part numbers but it wasn't relevant to these needles. I searched around a bit more and discovered that the first 'N' is just an OEM identifier, the '36' is the style of taper. The numbers aren't sequential and are often letters. There is no way to determine length and taper from this part of the number without a secret decoder book. The last letter is sequential and signifies the straight diameter. I saw several N36(x) needles on ebay. My bike already felt good off the line so there wasn't much need to experiment with straight diameters.

Since I couldn't find the info online, I pulled a needle from the carb and measured it. The straight diameter was 2.48mm which means that this 'N' corresponds perfectly with the 'N' straight diameter of the PWK28 needles. The length is also compatible. What dumb luck. I already have a large selection of these. Unfortunately, they are not in my garage at the moment. I pulled the JJS needles from the PWKs I took off the bike. It idled fine but as soon as I touched the throttle it would die. The 'S' has a 2.525mm straight diameter which is much too large (lean). The only other needles I had on hand are the "knockoffs" with no markings. They are supposed to be JJH needles and the diameters measured 2.43mm so they probably are.

HOT DAMN! Those needles livened up this bike like you wouldn't believe. Throttle response is razor sharp and there is no bog or hesitation anywhere. The only trick to fitting the needles in the slides was to use some plastic donuts from a set of BS34 needles as a spacer on top of the e-clip. Without the spacers the needles weren't held down by the slide springs. You could probably use the "nail heads" from the N36N needles as it looks like it's just pressed on there.
 
MrRiggs that is some great news. I had been looking for some different needles for these things but I really had no idea what to go with. One quick question though, are these needles adjustable and if so which position do you have them in?
 
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