New Carb problem

cowan.15

New Member
Dec 4, 2008
4
0
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South Australia
Hi, I bought a new cns carb from Spookytooth for my stock 48cc bike with 44T sprocket. With the old carb, I could pull max revs. With the new one, at WOT the bike is not reving out as much, like it needs more fuel. What is the next step I should take to try and fix the problem? Checked plug, and it is dry. Should I drill out jet, or move needle? thanks
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
Is the throat of the carb the same as the old one?

You could experiment with the needle a little, or try using the old jet/needle combination.
 

cowan.15

New Member
Dec 4, 2008
4
0
0
South Australia
Yep, sounds like the needle is the problem. Will try to swap it from the stock carb and see how it goes. Might be leaving the stock carb on since I'm going to be fitting a new expansion chamber I've got coming in. That way at least I know that the stock carb was running properly at one stage.
 

RLorange

New Member
Jun 21, 2008
127
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Australia
Yes that was me having problems tuning the CNS

Did you get a bog down at around 3/4 rev?

I have solved the problem and yes it was the needle, very good problem solving guys!

The needle has an odd taper which delivers too much fuel at high revs, maybe this was designed for engines with a shorter stroke or a 4-stroke engine or something...

Anyway the problem is solved by using the pin from your old NT. The CNS rips along now and my engine is much smoother especially at high RPM.

You might also want to lower the throat if your jet, like mine sticks out a long way.

So don't worry you haven't wasted your cash :)
 

RLorange

New Member
Jun 21, 2008
127
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Australia
I meant Float not throat!!

Oh and the jetting if anything is a little rich, looks to be 80+

and another thing: This carb has some open orifices which will let in water if it rains. I put little tubes on them and made a hole in the main filter to poke the tubes into. Also there is a silly over-flow/vent tube which leaked gas on mine. I blocked it up inside the float bowl using a plastic tooth pick. Created no problems and stopped the leak.

Finally, swap the pin clips over becasue the clip from the NT pin will not fit into the recess of the slide from the CNS. I also used a tiny washer as the best setting for me was in between the 2nd and top notch.

Hope this helps for anybody having problems with this carb.
 

stuartracing

New Member
Dec 9, 2008
488
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59
Gainesville FL.
I would say that the air/fuel mixture screw is for air since it is in the venturi part of the carb (int. side of the carb.), and not a fuel screw...So turning it out is giving it more air(leaning it out) and in is richening, less air.....????I just got my CNS and it was doing the previously mentioned quirks, bogging at 1/4- 1/2 throttle....I did the NT needle,clip ect.ect...Getting ready to go test...78 degree`s out here in FL. Jan...
Paul...