rubber-tipped BS38 float needle answer

[DogBunny]

The following is a documented direct replacement rubber-tipped float valve needle for 1972-1979 Yamaha XS2, TX650, and XS650 Mikuni BS38 carburetors (re-use your stock float valve seat):
Type K1 float needles as used on 1988-2008 Honda VT600C
Be sure to look for "type K1 needle" as opposed to K1 motorcycles which can refer to a lot of different things.
Jump to post 52 in this thread for a picture of what it looks like.

(original thread-starter
Seriously, how difficult would it be for Mikuni or someone else to start manufacturing and selling BS38 float valve needles that are rubber-tipped like the BS34 ones are?

 

[5twins]

Apparently there is a Keihin needle that will fit. Some info in these threads .....

http://www.xs650.com/threads/rebuilt-carbs-overflowing-random.15344/page-2

http://www.xs650.com/threads/help-getting-back-on-the-road.51909/page-7#post-587126

I've never tried one but it looks like gggGary may have. Maybe he'll report his findings? But, if it was a huge success I'm sure he would have. Looks like maybe it failed, lol.

 

[DogBunny]

Thank you 5twins. I reached out to gggGary and asked if he ever tried them.
As pointed out in postings in your second link, there are height and angle differences that I am leery of.

Seriously, why can't someone make what we want? It would be nothing for Mikuni to make them. Does anyone on this Forum have Mikuni's ear?
If MikesXS can find a manufacturer to make BS34 and BS38 needle repops, then why can't that manufacturer combine the two styles and make a proper BS38 needle that is rubber-tipped?
Does anyone on this Forum have manufacturing connections that could make this happen?

 

[gggGary]

I'm rooting for you DB!

 

[DogBunny]

https://www.ebay.com/itm/6x-Carbure...700684?hash=item1cff620ecc:g:wtkAAOSwR~VgDkgO
So, what the heck, they aren't really right, but I went ahead and bought the above needles that match those mentioned in the threads that 5twins linked to. Six needles for less than $9, plenty to play around with. I'll report back in 6 weeks when they arrive from China.

But, still, how about if someone with manufacturing connections finds someone to make a proper viton-tipped BS38 needle?

 

[Mailman]

When I first got my ‘77 and tore the carbs down for rebuilding, one carb had a Vito tipped float needle with the little wire retaining clip. I don’t know how well it worked, I replaced it immediately.

 

[5twins]

I'm not really that up on needle design but if the tip angle differs then I imagine the angle in the seat does as well, matching the tip angle. Maybe Viton needles use this different angle compared to steel needles. So, maybe what we really need is a Viton needle and seat assembly to fit our BS38s, one that screws in like the originals.

 

[DogBunny]

When I first got my ‘77 and tore the carbs down for rebuilding, one carb had a Vito tipped float needle with the little wire retaining clip. I don’t know how well it worked, I replaced it immediately.

That was surely the same needle that I just ordered.

I'm not really that up on needle design but if the tip angle differs then I imagine the angle in the seat does as well, matching the tip angle. Maybe Viton needles use this different angle compared to steel needles. So, maybe what we really need is a Viton needle and seat assembly to fit our BS38s, one that screws in like the originals.

gggGary pointed out the following regarding the tip angle to me, and I quote:
"They seat against a square corner not a tapered seat so the angle prolly not a big deal....."

 

[5twins]

Hmmm, well maybe modding an old leaky seat by grinding an angle into it might be the hot ticket? That would also let the taller needle seat in deeper. Maybe a Dremel bit like this would do the trick .....

https://www.homedepot.com/p/Dremel-...-Plastic-and-Soft-Metals-2-Pack-125/203641150

 

[DogBunny]

Hmmm, well maybe modding an old leaky seat by grinding an angle into it might be the hot ticket? That would also let the taller needle seat in deeper. Maybe a Dremel bit like this would do the trick .....

https://www.homedepot.com/p/Dremel-...-Plastic-and-Soft-Metals-2-Pack-125/203641150

That is a great idea. That Dremel bit looks good too.

 

[member28833]

took a few minutes at work to lightly clean a BS38 needle/seat with a q-tip for closer inspection. Here are a few pics-
Gotta go...-R

 

[5twins]

So, there does seem to be a very small bevel on the hole through the seat. I'll have to look at some BS34 Viton needle seats and see what their bevel looks like in comparison. If it's really small too then maybe this is a non-issue.

 

[DogBunny]

That BS38 seat bevel makes sense. If it wasn't there, the metal-on-metal seal wouldn't seal at all.

 

[member28833]

Actually let me share some past experiences with sealing. Years ago I made many many hydraulic valve "poppets" (needles) and seats. These were made out of mild low carbon steel (cheap stuff really) and then hardened before the sealing surfaces were cut. "Hard turned" cut at high rpm with diamond inserts. The sealing mostly depended on the roundness of the mating surfaces. Tool condition and collet cleanliness was important to achieve the necessary "roundness" for good vacuum air testing periodically.
I am a fan of metal to metal sealing.
It just has to be well made

 

[5twins]

Maybe that's the issue with many of the aftermarket replacement needle and seat assemblies. My dealer told me he quit using them because too many came back shortly afterward leaking, and he had to fix them on his dime, lol. He only uses genuine Mikuni needle and seat assemblies for replacements now.

 

[member28833]

Bingo

 

[gggGary]

Considering these are well used that edge is pretty sharp...

Note these do come in different opening sizes.

I'll make another shot at getting focus.

 

[gggGary]

Pics Take 2

from left aftermarket, while it LOOKS like it has a spring, plunger is fixed next 3; well used BS34, one is missing viton so you can see the tang that holds the tip.
last two are early BS38 out of the same carbs as seats above.

 

[5twins]

1.5 is pretty small. Did those come out of a 650? I thought 650's used 2.5's (early carb sets) and 2.0's.

 

[gggGary]

1.5 is pretty small. Did those come out of a 650? I thought 650's used 2.5's (early carb sets) and 2.0's.

Yes an XS1 carb set but, well you know...