NC30 Emulsion tube wear?

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Vincent
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Bike owned: '89 NC30 T1, '92 NC30 T8
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NC30 Emulsion tube wear?

Post by Vincent » Sat May 25, 2019 6:50 am

Hi team, had a glance down inside the rear carbs today and had a bit of a WTF moment when I saw the insane amount of wear in the top of what I believe is the emulsion tube.
It looks like the needles have worn a bloody massive groove into the lip/side of the emulsion tube here, anyone seen it this bad before? I've been chasing low RPM fueling issues for ages, and while I've got it running pretty nicely, there's a persistent stutter around 3kRPM that I can't get rid of, and that gets worse when I richen the A/F screws.
I'm thinking it's probably extra fuel making it's way up into the carb because the emulsion tube is so worn. Both of these cylinders run rich, with the right one (top photo) noticeably worse.

Reckon it's time for new needles and emulsion tubes?


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dirty30-2008
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Re: NC30 Emulsion tube wear?

Post by dirty30-2008 » Sat May 25, 2019 11:16 am

Hi Vincent.I probably am that "home mechanic" who like to have a go at anything before admitting I'm beat but..
The lips/groove that can be seen in your photos looks like it is meant to be there. Not something I have noticed before but the surfaces look like they are machined that way.I imagine at closed throttle the needle is low down in the emulsion tube and the lip allows the fuel that is drawn up around the needle to enter the carb body. May be totally wrong and will undoubtedly be corrected.....hopefully. That way we all learn . If anyone has their carbs on a bench please take a pic and we have a comparison

Best of luck.

hunter
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Re: NC30 Emulsion tube wear?

Post by hunter » Sun May 26, 2019 11:09 pm

That's pretty common in well used carbs,
Yes time for some new one's.

Vincent
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Re: NC30 Emulsion tube wear?

Post by Vincent » Tue May 28, 2019 2:19 am

Had a chat with Rick O, and it's not the emulsion tubes that are worn, it's the brass insert in the carb body that isn't a replaceable service part! Has anybody had any luck removing/repairing this part?

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fourfingers
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Re: NC30 Emulsion tube wear?

Post by fourfingers » Wed Oct 02, 2019 1:58 am

Vincent, just came across your post, so just in case: that needle jet is not worn by the needle, don´t worry. When assembled, the needle won´t get outside the smaller diameter hole, so there is no chance that was worn out.
I have a set of tuned nc30 carbs that came with that very same cut facing the butterflies.
Also, the needle jets are press fitted into the carb bodies, and can be replaced. Heating the carb bodies will help to press them out.
Cheers,
Emilio


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