borjawil
XS650 Enthusiast
Like the title says. Two different lengths needles in my carbs. Been quite some time since I rebuilt a set of these, but don't remember different lengths needles.
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Carb needles different lengths
- Thread starter borjawil
- Start date
yes both same length compare to this chart find correct needle for year of carbs.
Check needle jets too they are matched sets.
Check needle jets too they are matched sets.
borjawil
XS650 Enthusiast
Pretty numbers on them were the 4jn and 4n8. Weird. Guess I'll need to find new needles.
borjawil
XS650 Enthusiast
I'll have to double check but pretty sure it's 78-79. Has the bs38 carbs on it. If earlier years used bs38s why are their so many different needle and jetting differences? All the engines are the same besides the EI and points. I believe I have EI on this one.
Also found a kit with a needle, y267 is what they have it listed as
Also found a kit with a needle, y267 is what they have it listed as
78-79 are linked and have 5 holes on intake bell.
borjawil
XS650 Enthusiast
Yup those look like mine. On Mikesxs when I plug I'm '78, the carb float needles are rubber tipped and have the wire hook to connect to the float. Is that stock or an upgrade? Mine are the metal style with the spring loaded nipple on top. I have brass floats.
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borjawil
XS650 Enthusiast
Whelp looks like I'll have to reexamine my carbs. Not by them right now but pretty sure I have the 78 style bodies with the 5 ports at the mouth, and I know they're connected with the hose between them.
my slides are the angled ones which look likw they're for the 70-77 and earlier body, the needles are earlier and are retained with the plastic disc like the 77 and earlier slides would be. So the 78 502 needles won't fit since they're too long or so I've read. But are the needles too long due to carb body differences or just the needle jet differences (basically do I just get 502 needles and matching needle jets for the 78) 80 and new had flat slides, but I can't seem to find any pics of the 77-78 slides. Are they the same but different needle holding components? Guess I'll have to check my bowls for early or late style, and all my jets for sizing.
Also answered one of my questions on the float needle. Seems the rubber one is for performance carbs? Any benefit to using these instead of the metal ones, and can they be used with the same needle bowl fitting?
my slides are the angled ones which look likw they're for the 70-77 and earlier body, the needles are earlier and are retained with the plastic disc like the 77 and earlier slides would be. So the 78 502 needles won't fit since they're too long or so I've read. But are the needles too long due to carb body differences or just the needle jet differences (basically do I just get 502 needles and matching needle jets for the 78) 80 and new had flat slides, but I can't seem to find any pics of the 77-78 slides. Are they the same but different needle holding components? Guess I'll have to check my bowls for early or late style, and all my jets for sizing.
Also answered one of my questions on the float needle. Seems the rubber one is for performance carbs? Any benefit to using these instead of the metal ones, and can they be used with the same needle bowl fitting?
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Sounds like you have a set of Franken-carbs, lol, parts from many different years. Your bodies sound like '78-'79 ones, slides like '70-'77 ones. The difference in needle lengths is due to how they mount up in the slide. The '78-'79 slides mount the needles up higher in the slide so need a longer needle. If you compare how much needle hangs out the bottom though, all '74-'79 are about the same (about 33 or 34mm) - if the right needle is used. The '70-'73 needle (4JN19) would be about 5mm shorter.
None of the BS38s ever came with a rubber tipped float needle, but I've heard there are some that can be swapped in. I don't think it's a matter of them being for performance carbs but rather about how well they'll seal and how long they'll last. The rubber ones may be better at this.
None of the BS38s ever came with a rubber tipped float needle, but I've heard there are some that can be swapped in. I don't think it's a matter of them being for performance carbs but rather about how well they'll seal and how long they'll last. The rubber ones may be better at this.
borjawil
XS650 Enthusiast
Gotcha. So can I use any 70-77 matching needle and needle jet, and adjust my jets for lean/rich then?
Well, not quite. The '70-'73 4JN19 needles are too short and their matching Z-6 needle jet is too long, so those parts are out. The '74-'75 4N8 needle may be OK but you can't get it's matching short Z-6 needle jet anywhere. So, I think you'd need to go with the '76-'77 4M1 needle and matching Z-8 needle jet, then tailor the rest of the jetting around them.
Maybe someone was trying to do an xsjohn mod like the needles he used to sell. The right side gets slightly hotter so he adjusted the needle to compensate.
borjawil
XS650 Enthusiast
Just wanted to confirm before I buy that the mix screws and everything from the 76-77 to 77-78 were the same.
No, the mix screws differ and are unique to the '78-'79 carbs. You'll have to use them. They have a stepped tip and use an o-ring for sealing. None of the earlier mix screws have an o-ring .....
Mix screws don't usually need replacing but you might need new o-rings for them. Through trial and error, we've managed to track down the perfect replacement size .....
Mix screws don't usually need replacing but you might need new o-rings for them. Through trial and error, we've managed to track down the perfect replacement size .....
borjawil
XS650 Enthusiast
Only one if my mix screws had a spring in it. Springs I got with the kits are about the same length and diameter, but thicker metal and don't compress easily. Look like the 76-77 spring above where as the one in my 78-79 carb was tighter wound/more turns.
