Stock NT carb (Modifications Guide)

6blueoval9

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Having seen my first NT carb up close and personal it doesn't appear to be a bad carburetor providing it's used within its capabilities.

Right off the bat I pulled apart the air cleaner/filter assembly to find a host of turbulent air flow obstructions that are easily corrected.

The stock air filter itself can flow an abundance of air but doesn't appear to provide a very good job of filtering out smaller particles..just hold the filter up to a light and you'll see what I mean....From a performance stand point this filter is more than adequate to supply air to the motor.

One can simply suggest that you just go out and buy one of those high performance air filters which is fine or ,you can do these simple but effective mods to get more out of this 14mm carburetor.


If you have a stock motor or even a mildly modded motor and looking for a little bit more, this carburetor appears to be more than capable of accommodating that.

So here is what I've found.

(Obstruction #1)

The stock plastic seal has a number of turbulent air flow obstructions as you can see in the picture...just simply cut out the center, being careful not to accidently cut out the holes needed to re~attach the ring.
IMG_20171014_114847.jpg

This is what the ring should look like when cut properly.
IMG_20171014_121634.jpg
 
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6blueoval9

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For mod #2 I need to explain that this will eliminate your chokes function, possibly making it difficult to start your motor in colder weather...If you do not wish to eliminate your choke then do not perform this mod below.

My next obstruction I've found is the entry port of the carburetor.

Air is hitting the sides of the extended port entry, helping create turbulent air flow...Simply grind this extension down and radius the entry until you have a smooth transition for air to enter.

Now keep in mind that I'm not porting the entry way what so ever and the entry port still measures 14mm or close to that but will improve air flow quite a bit given its size limitations.

Here is the stock carburetors air intake side.... you can see the extended tube like extension of the bore ,this extension blocks air creating a turbulent flow into the bore...This extension is there so the choke flap has a surface to completely close off the bore and only breath through the tiny hole creating a very rich mixture that helps start your motor in cold weather.
IMG_20171014_115009.jpg


This is what it should look like after grinding down the extension and giving the entry port a nice radius.
IMG_20171014_133050.jpg

One more pic...notice how even the choke stop has been removed.
IMG_20171014_133516.jpg


For stealth looks you can leave the choke assembled or simply remove the entire choke assembly and fill the lever hole with jb weld or epoxy so no garbage or water can find its way through.

Other than tuning I wouldn't consider anything more needed to get the most out of this carburetor.

If you want a larger carburetor I would suggest going with the 16mm "Speed" version of this NT carburetor and follow the same mods shown here if you wish.

Edit:

Upon some discussion below on the subject of boring the carburetor..I may try this to see how far it can be taken without idling issues or difficulties to tune...I'd like to keep this a simple but complete guide to gain a little more performance out of your stock 14mm NT carburetor.

About that high flow airfilter, in all honesty using an aftermarket air filter would help perform better as air isn't just drawn in from the bottom such as with the stock air filter cover but more so drawn in from 360 degrees providing a better direct flow of air in general to the carburetor and, will have better filtering capabilities.

Thanks for looking.

Edit: More to come.
 
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6blueoval9

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I've bored out nt carbs for stealth builds, they can take a surprisingly large bore.
I've read conflicting stories on boring them out...Some say this changes the fuel metering making it more difficult to tune and dealing with the slide leaking air around it.. others say it works..lol...I'd rather not bore one out..I've measured a possibility of 18.79mm of bore....the slide would leak air around it like crazy in my opinion.

I'm gonna try it at 14mm and then pickup a 16mm speed version to try out with the same mods.
 
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mybike

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Jul 6, 2017
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I love the NT Speed Carb. I tried different carbs and always go back to the NT / NT Speed. I think Steve on the forum feels the same.

Video of NT Speed Carb.

 

butre

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I've read conflicting stories on boring them out...Some say this changes the fuel metering making it more difficult to tune and dealing with the slide leaking air around it.. others say it works..lol...I'd rather not bore one out..I've measured a possibility of 18.79mm of bore....the slide would leak air around it like crazy in my opinion.

I'm gonna try it at 14mm and then pickup a 16mm speed version to try out with the same mods.
air leaking around the side just results in a higher idle. it can be accounted for
 

6blueoval9

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It can but I'd rather have a normal idle and it takes away from the simplicity of this carb in a way.

What's the largest you've bored one out to?
 

6blueoval9

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You're talking about the exit side right?...when I look down the entry side the floor of the port is maybe one millimeter from the floor the jet sticks up from...not sure how you could get 3mm more on the entry side full circumference.
 

Street Ryderz

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Oct 14, 2016
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You're talking about the exit side right?...when I look down the entry side the floor of the port is maybe one millimeter from the floor the jet sticks up from...not sure how you could get 3mm more on the entry side full radius.
I remove the emulsion tube and bore straight through then epoxy the tube back in place on the nt.
 
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