Stock NT carb (Modifications Guide)

curtisfox

Active Member
Joined
May 13, 2010
Messages
620
This is KOOL! And maybe do the same for a 4 stroke. For what it is worth i used some base ball bat tube and made intake, ( witch is tapered ) with proper flanges to fit 4 stroke. Small 4 strokes 5/8 to 2 hp. All fun stuff.

Also seen it done with the larger part of the bat for velocity tube...............Curt
 


Steve Best

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Joined
Sep 22, 2012
Messages
1,236
I didn't do much with the NT other than rejet it. The bore was the same size as the steel manifold and port so I didn't see a gain in enlarging it. What I did work on was intake tract tuning. This picture may look kinda crude, but so are many of my "proof of concept" experiments. It is a piece of copper pipe JB Welded to a cap over the carb inlet with just enough clearance to let the choke still work. Then I experimented with different sized plastic bottles to see their effect on power.

A long tapered bottle gave great low end power but killed top speed and speed on hills. For whatever reason this waterbottle gave the best top end power in the 7000-10,000 rpm range without hurting low speed power. It was better than no carb filter at all. The filter is simply open cell foam squeezed inside and didn't hurt performance either. Crude, not very pretty, but effective. KC must be cringing at my lack of aesthetic taste!

BlueOval, you are chasing the ideal. Modifying to what looks like a good idea. This is good, chasing a theory, but you have to test in between steps. So does it actually work better? or just look better to our mind's ideal? You have to test in an unbiased way to really know.
 

6blueoval9

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Joined
Aug 28, 2017
Messages
1,120
I didn't do much with the NT other than rejet it. The bore was the same size as the steel manifold and port so I didn't see a gain in enlarging it. What I did work on was intake tract tuning. This picture may look kinda crude, but so are many of my "proof of concept" experiments. It is a piece of copper pipe JB Welded to a cap over the carb inlet with just enough clearance to let the choke still work. Then I experimented with different sized plastic bottles to see their effect on power.

A long tapered bottle gave great low end power but killed top speed and speed on hills. For whatever reason this waterbottle gave the best top end power in the 7000-10,000 rpm range without hurting low speed power. It was better than no carb filter at all. The filter is simply open cell foam squeezed inside and didn't hurt performance either. Crude, not very pretty, but effective. KC must be cringing at my lack of aesthetic taste!

BlueOval, you are chasing the ideal. Modifying to what looks like a good idea. This is good, chasing a theory, but you have to test in between steps. So does it actually work better? or just look better to our mind's ideal? You have to test in an unbiased way to really know.
I'll have an untouched NT to compare the difference with...Nothing I've done so far has been tested NOT to work in different venues of use.

Removing abrupt turbulence is certainly an improvement with air flow in anything and a velocity stack is proven to help as it removes this turbulence...I'm highly expecting these mods to be an improvement without the need to test first but I will test the difference and report it.

That bottle mod you have I would consider (based on the taper) to have improved your performance based on the same principle a velocity stack would.

You saw in the beginning of the thread I wanted to get rid of barriers and edges inside the intake area of the carb to improved air flow...I'm sure the first two steps alone would have been an improvement but decided why not go all the way with it so, I completely eliminated all air flow turbulence by just creating a built in velocity stack..really it only amounts to two modifications when completed...removed the garbage center piece on ring and a built in velocity stack.

Cost me a whole $5.00 with tax from Walmart...I bought a package of the jb weld steel stick epoxy/ putty...gutted and scuffed up the area I used it on and rough molded it by hand then finished it with a sanding roll.
(Gutted)
IMG_20171018_222809.jpg



I'm actually considering some changes with the inside of the filter cover..I may make some changes to re route directly how the air is sent to the carburetor after being drawn in...The part I like best is it will all look like a stock carburetor installed which it would be, just an improved one.

As far as the bore, ultimately I'd like to be at 17mm once I take the build further so, most likely an NT speed carburetor with .5mm taken off the circumference should yield me 17mm and not effect idling or disturb the pressures to siphon fuel...or just a different carburetor all together but I will try the speed carb first.
 
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6blueoval9

Well-Known Member
Joined
Aug 28, 2017
Messages
1,120
This is KOOL! And maybe do the same for a 4 stroke. For what it is worth i used some base ball bat tube and made intake, ( witch is tapered ) with proper flanges to fit 4 stroke. Small 4 strokes 5/8 to 2 hp. All fun stuff.

Also seen it done with the larger part of the bat for velocity tube...............Curt
I've seen an aluminum bat exhaust on you tube.:cool:
 
K

Koz

Guest
Thank you 6blueoval9!
My bike wasn't getting past 26 mph unless I took off the filter. Then it would hit 32. I made the mods to the plastic cover, and now it breathes much better.
I was so frustrated, trying to change needle settings, etc.. It was that air flow turbulence issue!
 
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