VM29 Jet block thread size

Does anyone know the emulsion tube thread size/pitch in the 29mm smoothbore jet blocks?

I dont know if this helps or not but, my cheap thread gauge came up with 0.75. I believe its 4mm.
Emulsion tube being the needle jet tube? right. Part 42?

Yes, emulsion tube is the needle jet.I pulled one out and it's not M4, it's M6x.75. I found the tap today. Thanks for checking on that moneypit.

Well it turns out that M6 x .75 is not the correct thread pitch for the jet blocks. WG carbs used to offer a jet block repair service, it is not longer listed on the web site. He WILL NOT give out that information on the telephone either. What is up with this Souper Secret thread pitch? If anyone knows this info, please pass it on. I am in the middle of a jet block repair and ran into this snag.

EDIT: M6 x .75 D3 is the correct thread size and pitch for the jet block. I was using a cheap used M6 x .75 tap made in China when I did this step. It turns out the tap wasn't cutting the threads with the correct clearance being the reason my needle jet wouldn't thread into the brass. A new D3 class tap cured this problem allowing a perfect fit for the needle jet( emulsion tube).

I have 1 VM29 NOS jet block I will sell if interested email me direct b.flood@myactv.net

Am uncertain, but reportedly 6 x .7mm threads (see link below).

Uncommon size tap may be difficult to find.

www.labusas.org/forum/showthread.php?152...ikuni-29mm-soothbore

Good Fortune!

www.z1enterprises.com/ItemDetails.aspx?i...ck&item=ZSMVM29%2f10

Thanks Patton, I'm looking into that now. Still not certain it's the M6 x .7 thread that is mentioned in that topic you posted here . I do know that it isn't M6 x .75. I have that tap, and the needle jet doesn't fit that thread.
That topic lists WG's jet block repair as what he ended up using. He mentioned the product looked off centered, and then posted pics. The pics weren't available for viewing, and he never followed up to say that it worked in his carb.
I remember WG offering this service, with detailed information on his website describing his process.

etbike, I have seen that jet block listing. I'm working to make a repair that will not end up like the original pot metal jet block with stripped threads from heavy handed GOrillas changing Mikuni jets in their smoothbores (LOL). Purchasing a new, or used jet block will be my last effort. Thanks for contributing.

I know there is a Mikuni guru among us that knows this thread pitch. I will most likely have to cut single point threads in a lathe once I determine correct pitch. There doesn't appear to be a tap readily available .
Ahh, I miss my Hardinge precision lathe.

www.projectsinmetal.com/wp-content/forum...ander-m/IMG_1872.jpg

is it a coarse or fine pitch? like 6x.5 6x.7 6x.75 6x.8 6x 1.0

kawi810 wrote: is it a coarse or fine pitch? like 6x.5 6x.7 6x.75 6x.8 6x 1.0

It's fine pitch. From all indications the pitch is .75 , gauging it with my Starret thread gauge. The .7 is clearly not fitting the threads as well as the .75 . The .8 is off too. I'm going to get a different M6 x .75 tap and see what I can come up with. Thanks for the input every one.

I ended up with a new M6 x .75 tap with D3 class thread made in USA. Needle jet threads into it perfect. I sunk a nice piece of threaded brass into the jet block and ended up with a much better piece than any I could buy new.

I realize this is an older thread, but I'd like to ask Black Z!R a question about this repair.  More specifically, did you thread the OD of the brass insert, and if so, what thread size?  From reading the thread, I'm guessing yes.  Anyway, if anyone knows how to reach BlackZ1R, please share.  He hasn't logged in for almost a year, and I'm not sure he'll see this message.

Edit: I made an insert with 5/16-24 threading on the OD, and the Jet Block was likewise threaded on the ID, to accept the insert.  Looks like a good fix.  8mm threading would have also worked, but I didn't feel like buying a bottoming tap.