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Carburetor Jet as Nozzle

Posted by ZachHoeken 
Carburetor Jet as Nozzle
April 07, 2007 02:45PM
So after reading the post by Sid on simplification, he really got me thinking about using carb nozzles (the proper terminology is : Carburetor Main Jet) as the head for the extruder. I basically know nothing about this topic, so I set out to do a bunch of research. Heres what I found out:

1. Cars dont use carbs anymore, however motorcycles and ATV's do.
2. Auto people are quite unfriendly, especially when you are asking general questions and dont have a make/model or part number handy.
3. This crap is hard to find on the web.

However, I did find out some good stuff. First off, there are two main manufacturers we are dealing with: Keihin and Mikuni.


After looking at the parts, it seems that we'd want to go with a Mikuni, as they seem to offer smaller nozzles. They range from #50 to #700, however those numbers mean nothing to me. I've had a really rough time finding out what those numbers even correlate to. I cant find a product spec sheet to save my life. If anyone could, that would be excellent.

On the plus side, they are really cheap, if you find the right place. I've seen a couple sites that offer a 4-pack for $2.50. I'm going to order a variety of nozzle sizes to try out.

I'm leaning towards the hex style jets because it seems to me like the notch on the others could lead to problems with jamming and plastic buildup. also, you cant shape the head how you like because you need that ridge to screw the nozzle in/out. With the hex ones you could shape the head with a dremel and still be able to get the job done. I'll probably order various sizes to test and see which one works best.

They are all threaded, and as far as I can tell it seems to be a 10/24 thread. I dont have a clue what that means, but i figure once i get one I can go to the hardware store and find out what nuts fit it and get a tap/die set to make the matching threads on the rod. either that or you could use two nuts to attach it to the barrel. i'd prefer to screw it directly into the barrel however.

Anyway, I'm ordering a 4-pack from [www.bikebandit.com]. If anyone can find a better deal than them, please reply back.

Also, if anyone can find a spec-sheet to go along with these that would rock too.
Re: Carburetor Jet as Nozzle
April 07, 2007 04:40PM
I don't know much about carbs but what I can remember from the Ladybird book I read at school is that these nozels form a valve closed off by a needle attached to a float. For that reason they have a concave end to receive the needle. I think the extruder needs to have a convex nozel otherwise the outside of the nozel will collide with the plastic already laid down.
Re: Carburetor Jet as Nozzle
April 07, 2007 05:39PM
true, and a very good point. i plan to solve this by using a dremel or file to round out the end of the carb jet. its a very slight concavity, and the nozzles are made of brass so it shouldnt be too hard to fix that. (this is also why i opted for the hex ones rather than the slotted ones.)

this should work out rather nicely, as grinding a nozzle was part of the previous steps for using it. except now we've eliminated the step of having to drill out the tip... that is quite a pain.
Re: Carburetor Jet as Nozzle
April 12, 2007 11:37AM
Hi Zach..

I got that idea from the Weber 44idf carbs I once had in my car..
see picture upper left.. new quite expensive

but any beetlestore should have a fistful used ones for a few cents,
as I said I got them for 50cent/each
they are not threaded but threadable winking smiley
Go and ask for weber (vw-beetle (not the new.. the original), porsche.. even better VW-Porsche) or dellOrto (Vespa, Lambretta) that's the nozzles I messed around with some time ago

Re: Carburetor Jet as Nozzle
April 12, 2007 03:09PM
You guys do know that the 0.5 mm channel to the external side of the extruder needs to be very, very short ... less than a millimetre if possible. Otherwise the friction in the channel makes it very hard to pump any polymer.
Re: Carburetor Jet as Nozzle
April 12, 2007 03:15PM
Is the amount the filament expands after it has left the nozel related to the length of the hole or is it just a property of the plastic?
Re: Carburetor Jet as Nozzle
April 12, 2007 07:42PM
good point. if the nozzles are too long, i can always drill them out at 3mm to the desired depth.
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