Urban Express Carburetor Question

Hey all,

I've just finished resurrecting my first Express NC50. I think it came out very well. I am working on my first NU50. After thoroughly cleaning the carburetor and studying the service manual, I've come to realize the oil inlet tube is missing. Maybe one of the previous 200 owners was a ham-fisted knucklehead and broke it off. I am going to assume there's no practical way to put a new oil inlet in there. Or is there? Attached is a picture of a different carb with the 90 degree bend oil inlet. (Which is missing on mine.)

So now do I remove the oil pump and run this carb on pre-mix? Assuming I can plug the carb oil inlet for pre-mix duty, or go with a Delorto carb Party from Treats? I'd really like to keep the oil injection if I can but I'm not married to the idea.

Also does running the Delorto carb and matching intake keep the machine in fairly stock performance trim (with which I am OK)...

Thank you all for the benefit of your experience and wisdom.(edited)

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Re: Urban Express Carburetor Question

Lets see a pic of the actual carb in question .

Is the oil inlet simply not there by design or is it broken off ?

Re: Urban Express Carburetor Question

Captain Janeway /

I'm with PD, let's see it. Even if you run premix you don't have to remove the pump. Just plug it off and leave it. I'll get a picture of mine later. 1) I just run the inlet hose (coming from the pump) into the outlet hose(coming off resevoir), and then 2) have the injector piece you're missing plugged off (I just cut a piece of the hose already on it and ran a screw into it. It's been fine).

Some people use the rubber expansion plugs, but I've had the damned things pop out (you can't tightened them too much) and so have other people.

Re: Urban Express Carburetor Question

Sure! Here is a shot of the carb. You can see two stake marks, top and bottom, where a previously installed part was secured in place.

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Re: Urban Express Carburetor Question

Could you tap it and install your own fitting of some sort?

Re: Urban Express Carburetor Question

That could be made functional without much ado .

Maybe a bit of 1/4" copper tubing and petroleum proof sealant .

Or even a plastic 'L' might be able to be simply pressed in the hole .

Always more than one way around a bush .

Which ever , be sure there's an open path for the oil to flow where it has to go .

Clean it well and run it . ;)

Re: Urban Express Carburetor Question

Thanks for the input. I really appreciate your help.

I think I've got it solved. The opening is the same diameter as a tap drill for M5 X 0.8 thread. So I tapped it for M5 thread. Tomorrow I'll go to my buddy's machine shop and drill a 2mm hole down the axis of an M5 machine screw. Cut the head off the screw, thread it in with Loctite Blue, and fit the oil line over the end. Problem solved. With about 10 or 12mm of thread penetration, that's never coming out by mistake.

Pictures to follow.

Re: Urban Express Carburetor Question

Yes Mike! You and I both came up with the same idea, methinks, at the very same time. Thanks!

Excellent!

Re: Urban Express Carburetor Question

Step one. Thread the hole. Done.

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Re: Urban Express Carburetor Question

Always ... ;)

Re: Urban Express Carburetor Question

Captain Janeway /
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Here's the looping of the inlet to outlet tubes I mentioned. No point in pulling the pump

This was my block off on the injector but it looks like you have it handled

Re: Urban Express Carburetor Question

Thanks very much! Those are some nice close-ups. I appreciate your posting these.

I had no choice but to pre-mix my NC50 as it didn't come with a pump. But I'd like to try to keep the injection feature on this, my first Urban Express. The styling of the Urban Express is winning me over. I am already imagining where I might find another one. I fear this moped affliction is located on a slippery slope.

I was bit taken aback by the complexity of the mechanical auto-choke device. I'll replace all the hoses to preclude any leak problems. But the choke box itself, are they pretty dependable? I read somewhere you don't want to take the box apart. Good advice? Thanks everyone, much obliged.

When I get the M5 screw out of the lathe with a neat hole down the middle, I'll post up a picture.

Re: Urban Express Carburetor Question

Downhill Harvey (OFMC) /

> Jeff Adams Wrote:

> ------------------------------------------------------- I fear this moped

> affliction is located on a slippery slope.

>

> I I read somewhere you

> don't want to take the box apart.

>

You're already aflicted, prepare to have your life ruined.

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I took my choke mechanism all apart, and cleaned it. Not complex at all, it's just a piece of spring steel, hooked to a rod.

Re: Urban Express Carburetor Question

Thanks for the encouragement! To both ruin my life with mopeds and to look inside my auto-choke.

It seems strange to me that after more than forty years of messing with "big" motorcycles, I could just now become enamored with tiny ones. I enjoy the shit out of working on and riding these things.

Yet most of the time I am riding a 100 horsepower, street-legal dirt bike with nearly 10 inches of suspension, variable traction control, and switchable ABS. Honestly I can't believe I didn't start mucking about with mopeds years ago.

Melius sero quam numquam, I suppose.

Re: Urban Express Carburetor Question

Maybe you're just completing the circle ? ;)

Re: Urban Express Carburetor Question

Beyond the bimetal valve one of the biggest failures of the auto choke is that the bystarter chamber (the round rubbery one) is supposed to have a lightly oiled filter inside. The amount of air flow restriction inside that box will have a big affect on the mixture while the auto choke is active. Try partially covering the inlet hole to see what I mean.

Re: Urban Express Carburetor Question

That must be it! Thanks for the insight!

Re: Urban Express Carburetor Question

Yeah, if you look at the diagram and then hold the parts in your hand you will begin to see that the choke system draws air past an enrichment passage in the carb but it brings it in from the long and winding network of tubes that leads through the bimetal valve and then to the bystarter chamber. The second connection to the bystarter directly from the carb is a vent if I remember correctly, but don't quote me. When the engine is cold there is a strong vacuum signal to the bystarter and as it warms that signal is closed off by the bimetal valve. The Vacuum signal that powers the system is also where the rich mixture is delivered. The connection above the float bowl is just drawing raw fuel from the bowl.

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Re: Urban Express Carburetor Question

Wow. That is extraordinarily educational. Thank you so much. I think I get it now. I can see it working. At first I thought only air passed through those tubes, but no there's fuel in some and air in the other. Got it.

Yes it appears I have fallen completely into the pot of moped stew. I did not see it coming this morning but I just bought a Testi Comfort 50 in Vermont. Turns over but no spark. Under 300 miles on the odometer. I can't wait to dive into that but it will have to wait. I have the NU 50 on the work table right now. And I think there's a Moby 50V in the shed which will be next on deck. That whole pivoting motor thing is hysterical. Can't wait for that one either.

Again, thank you all tremendously for taking the time to share your knowledge and experience with me. It is appreciated.

Re: Urban Express Carburetor Question

Hey all. Apparently trying to drill a .070" hole down an M5 screw isn't all that easy even with a lathe. I haven't given up on that but I tried another approach today and it seems to have worked.

I tapped the hole with M5 X 0.8 where the 2-stroke oil used to go into the carb. Then I got some 3/16th copper tubing. A foot of it cost $2. Sanded down an inch or so of it, enough to engage an M5 X 0.8 die. Threaded the copper tubing and screwed it into the carb. It seems pretty sturdy. It think this will work. I haven't trimmed it to the length or position I want yet but it's screwed in tightly.(edited)

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Re: Urban Express Carburetor Question

Captain Janeway /

Nice. just bend it and plug it in.

Re: Urban Express Carburetor Question

Plus it has a nice steampunk look to it!

Re: Urban Express Carburetor Question

Epoxy is your friend. Like Brylcreem, a little dab'l do ya.

Re: Urban Express Carburetor Question

Be sure that the tube is not screwed in far enough to be blocked by the inside of the carb . Bottomed , so to speak .

You might think about hack sawing a couple of slots in the threaded end to insure oil passage . The tube end would look similar to a castle nut .

Re: Urban Express Carburetor Question

Indeed it's a miracle substance. In this case I am using threads to keep the copper tube in the carburetor. Better yet, it's easily removable and replaceable. If I wasn't able to thread the carb and the tube, you betcha. I'd epoxy that sucker in a second.

Re: Urban Express Carburetor Question

Good call. I too had the same concern. So I only threaded the copper tube for 2/3 of the length of the threads in the carb. I opened the threaded end of the tube with a countersink bit and then screwed 'er in just a bit more than half the length. Should be good to go.

Re: Urban Express Carburetor Question

> Jeff Adams Wrote:

> -------------------------------------------------------

> Good call. I too had the same concern. So I only threaded the copper

> tube for 2/3 of the length of the threads in the carb. I opened the

> threaded end of the tube with a countersink bit and then screwed 'er in

> just a bit more than half the length. Should be good to go.

Agreed . You should be ready to roll . ;)

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