EX-500 Carbs: Spring Length?

Tweeking. I'm off the map trying to get needles to tune up, bike wants a leaner taper than is available. Maybe I stretch the springs if they're not up to spec, add a little more pre-load, slow down the needles a bit.
 
Think I found the issue: My springs are 80mm long, 14.8mm diameter, 0.7mm wire.
Carb ID#: V334DB15

Do I start stretching until things work with normal needles, or just order some replacements?

Thanks for measuring!
 
Player 3 has entered the chat:
140mm length
14.5mm diameter
0.7mm wire.

Got digging in my stash, found a set of slides & springs. This could get real interesting.
 
In my case the bike did not have stock carbs, it had Mikuni VM36 carbs. I wanted to use the VM’s on something else and the GPZ/EX 500 carbs at the time were reasonably easily come by and not too expensive. There is a good thread here on the changes needed to get them sorted and people were getting good results. I did as well.

The GPZ carbs are a newer design and lighter than the stock carbs. They are not considered a performance upgrade but will work on 650’s and 750’s. I have now got another set to free up some more VM36’s.

If your stock carbs are in good order stick with them. If they are not in good order the GPZ/EX carbs are an option but it could work out cheaper and easier to service your original carbs.
 
Well, now I feel like a right s#!t. I've been messing with these carbs since 2015 or something and tonight they're finally running right.

Stupid 80mm springs....
Stupid long springs sitting in my basement...
stupid brain forgetting about stuff....

Stupid...

Going to take a little cleaning and plug reading to verify things, but they sure felt great. Maybe a touch rich, but that could be a plugged air jet. Been a while since they've seen the can of Chemtool.
 
I'm pretty new to xs650s
Can someone tell me why these carbs are used by many instead of the originals?
In my case, because I couldn't keep throttle shaft seals in the original BS34's for more than about 4 months at a time and they always felt lazy and sloppy.
The only thing better the BS34's did is the starting enricher circuit, that was dialed in for the engine. the Ninja 500 carb enrichers work, but they're not moving enough fuel for the engine.
 
Let's don't jump to conclusions just yet. trying to borrow a vacuum gauge to make sure the slides are getting all-the-way up. Intake noise was suspiciously absent last night, makes me think the velocity through the carbs is higher than it might need to be. Maybe a GoPro staring down the throat would be good as well, but I don't have one of those either. Nice to know the 80mm springs were WRONG. haven't ruled out buying a pair of 100mm 'right' springs if I can find 'em.
The good news is, right plug looked pretty nice. Left plug was black-n-shaggy around the rim, think we gotta do some cleaning and float checking on that side.
 
You're probably on-track with that. depends on stiffness a bit, but it seems the wires are all about the same diameter, so I don't think we'd expect much change there. maybe number-of-turns/ length of wire. I'm not up on my spring physics.


Some double-checking today, didn't get the right side diaphragm sealed all the way. there's my trouble. threw some Chemtool at the air bleeds and things are better now. Bike runs much better. Probably get to drop the pilot jets a size, maybe trim a little off the springs.
Still surprised with how much quieter the intake noise is now.
 
OK, the 140mm springs had a bit of a hesitation at like 4-4,500 RPM, likely lean 'cuz the needle was still in the main jet.
The 80mm springs had a rich hesitation at like 3,400 RPM, cleared up about 4K, needle rose too quickly, too much fuel until the engine caught up.
So I went out on a limb, found 100mm CVK springs on eBay for $9/ea, installed them.

This is the way. smooth pull, no hesitation at the needle-to-main transition. We should add this to the Tech page. ;-)
 
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