VM28 Carbs - 5I4 Needles Unobtainium?

[BlueR32]

Curious to know if there's any other options for the 5I4 needles?

[m in sc]

im pretty sure these interchange . however i never bought a set. https://www.ebay.com/itm/162890216371

[1976RD400C]

I have a pair of 5I4 needles from RD250 carbs if you have your heart set on that particular one.

[BlueR32]

I have a pair of 5I4 needles from RD250 carbs if you have your heart set on that particular one.

PM sent

[1976RD400C]

Faint stain on one

[BlueR32]

No worries about the stain! Just replied to your PM. Many thanks 

[BlueR32]

im pretty sure these interchange . however i never bought a set. https://www.ebay.com/itm/162890216371

Just received the 5I14 needles from Niche Cycle. They are about 5mm shorter than the stock 5I4.

[m in sc]

well, shit.

they are pretty good about returns

[BlueR32]

Well between the 20% restocking fee and the return shipping it's hardly worth returning. If anyone has a use for them let me know!

[IR8D8R]

Someone pulled a 5I14?

[m in sc]

I thought they were possibly compatible for some reason. i just dave f the carbs, i haven't run stock needles in forever

[IR8D8R]

5I4 are stock for the 73 RD350 but they discontinued them. That sounds unlikely but here we are. Chuck was looking for some for my 350. We both were, but they do seem to be scarce. I will probably never know how well they would have worked.

AI response is interesting:
<<Because the 5I4 jet needle was custom-engineered by Mikuni specifically for Yamaha's OEM production lines, it does not have a direct, universal aftermarket counterpart in standard Mikuni part catalogs. If you need a replacement, you cannot simply order a standard Mikuni 5-series catalog needle without altering the bike's mid-range performance profile.
 If you are struggling with the notorious mid-range "burble" or rich stutter common to the stock RD350 jetting profile, the most highly recommended swap within the vintage two-stroke community is to switch to TR-1 specification needles (?? Never heard that before). Historically, vintage enthusiasts discovered that a shorter, more aggressively tapered needle from early 1970s Yamaha "TR" series trail/enduro bikes (like the TR1 or early DT/RT models) could be fitted into the RD350's Mikuni bodies.>>
 Then it goes on to contradict this as a misread and suggests the notorious Keyster needle is an exact copy of the 5I4 and says to use 5DP7 or the still available 5L1 which were allegedly used in UK/EU area RD350's(?).

 Anyone heard of the "TR-1 needle mod"? I found references to that elsewhere. That does give some reasoning for a shorter needle. But the Dave F mod seems to add tune-ability and 5DP7 needles are common. How about 5L1 needles?

 The VM-28-419 flat slides were a better solution in the end and basically a direct swap for me using stock cables and manifolds. After trying 3 different sets of RD carbs. Dave and no Dave without any notable difference in midrange behavior it was welcome. Obviously a more costly option than finding needles but they run better than Dave F. modded carbs on my RD.

IR8D8R

[BlueR32]

My understanding is that the Dave F mod only applies to RD350 & 400. Is this correct? (I have the RD250 motor with VM28 carbs on the SRX/RD hybrid project)
https://www.2strokeworld.net/forum/index.php?topic=3909.75

[m in sc]

itll work. i did an rd250 w dave f mods years ago, it worked well.   

[m in sc]

and the yl1 is a correct replacement for a uk model 75 350b. these also used a different jet tube and a brass ball blocked air jet that had tubes to the airbox. yes. a 75 b model. no idea why the uk got this and us didn't.

having have recently experimented with a set of 'stock' carbs, then dave f carbs (dale alexander actually, which is where the td reference comes from), and sto k carbs vs flatslides, the flatslide pwks are a smidgen better with the jjh needle.  the biggest difference was actually made with changing the heads to the torroidal cut vp heads.  this is with unported cyls and fpp chambers. they come on about 6500 but the midrange smoothed out dramatically w the head swap. im not suggesting it as its really expensive.  but it was that last piece.

my goal was to see how good i could get a set of unported cyls to run w just bolt ons.

a 3d printed y boot with divider ports helped as well, and it fits the pwks correctly, to a large k&n.

the cdi is set to drop off the ignition over 7k down a bit and this really helped with the higher rpms.

tgis setup is sort of my test mule bike so its constantly changing
.

this was all done changing one thing,then running thru carb settings,, then changing something else, then back thru the carbs again, etc etc..