CNS Carburetor

[Techbiker]

I bought a CNS carburetor and initially I had quite a few problems. Recently though, I rejetted the jet a few sizes smaller to a 70. I was confused when it seemed to bog down when I went up hills like it was really lean considering that it appeared to be really rich until 1/2 throttle.

I then read this thread and tried switching out the CNS needle for the NT stock carb needle. Now power is great and the A/F ratio is almost spot on until 1/2 throttle before bogging down. I plan to move the c-clip up one to lean it out a little more and then drill out the jet one size larger. If my theory is correct, this will give me great performance throughout the entire range.

It appears that the CNS carb stock needle is just too thin. It lets in way too much gas from closed to half throttle. The result is that even when the jet is too small your mixture is too rich part of the time. It looks like the fix is a thicker needle that lets in less gas at the right time. Then just rejet the main jet like normal so that you are getting a good amount of gas at full throttle. Finally, tweak the c-clip a bit and then tune the carb with the A/F screw on the outside.

My CNS carburetor does not appear to leak at all.

Hopefully this will help solve many people's problems with the CNS carburetor. I have not found a way to get the throttle cable length corrected yet.

 

[wildemere]

I fixed my way to rich CNS by cutting 2mm of the botom of the slide and seting the cutaway at 2.5 mm.

The clip is on the top notch and the air screw is 1.5 turns out.

Main jet burns a nice tan and I can increase mixture on the fly with the choke.

It seems the only thing right with this carb is the main jet (66cc at sea level) everything else needs tuning.

Also the air screw affects overall mixture slightly, not just idle.

 

[psprat496]

Ok...So should I buy the carbeurator? I want some upgrades but is it worth it?

 

[skjjoe]

Not unless your willing to modify it

 

[bairdco]

looks like they should change the name of it from CNS to CNWS (Carbs Not Worth S#%*)

hey Techbiker, here's your throttle cable solution...:http://motorbicycling.com/f39/norm-shortening-throttle-cable-9010.html

 

[Techbiker]

Bairdco, thanks for the link however I do not have any of the special tools that Norm is using. Do you think that I could use a washer as a spacer to take up some of the slack in the line somehow?

Today I also got a chance to tweak the carburetor. I did what I talked about in my previous post and moved the c-clip up to the leanest setting and rejetted the main jet a size larger. Now, my engine is still a bit on the rich side, but it is less so than before. When I ride up hills it no longer loses power although I can tell that it would like to be richer when under load. Overall I gained a noticeable amount of performance and the adjustability in the carburetor is nice, however I don't believe that it is worth $50. If it didn't come with the offset intake I would recommend against it due to price. However, with the offset intake manifold I believe that this carb is a decent in general and almost essential for a bike with an expansion chamber.

 

[skipu]

After playing with my CNS carb and it not running I had to remove it and installed the stock carb. While i had the carb apart i tracked down where are the nipples lead to. From what i can find online they say to leave them open but one of them runs into the bowl.....hmmm doesn't seem right to me. So now that the bike is up an running again i am going to stop in an dsee the lawn mower guy tomorrow and see what he has to say about the carb i am thinking they may need to be capped or bipassed to complete the vacume in the system. So until tomorrow.....

Stuartracing try calling your local yamaha dealer modle should be a CY-50 or CY-80 honghua pz15j

i run these carbs on 2 of my bikes with no problems easy tune airbleed i love it and the top nipple you can cap the other 2 are just venting 2 pieces of tubing and run them where you do not want the excess fuel to drip out im pretty sure on the yamaha motors top nipple was for oil injection

 

[bairdco]

techbiker, special tools? some solder, a torch, cable cutters and a file are all you really need.

i suppose you could shim it up with a washer or something. if you could find a little piece of tubing the same size as the cable housing, you could cut it to the length you need, cut a slit in it and slip it in.

 

[Venice Motor Bikes]

If you can't get the stock carb working right, you aren't going to get a more complicated one tuned either.

Better advice has never been given!!!

Most of us here in So Cal run the stock carbs & our bikes fly!
First learn how to tune the simple stock carb, & then step up to a more complicated carb,(that also needs to be tuned.) & that's if you even feel you need one after you get the stocker running right

 

[Dave31]

I get a lot of PM's from members who have purchased after market carbs and have trouble getting there bike to run.

I think many get confused that they can buy these carbs and then just mount them and ride and expect it to better then the stock carb.

 

[mountain80]

I avoided the cns as you cannot purchase needles and such for them. Spent a bit more for the dellorto but was well worth it

 

[the willi]

use venices ideal, because if you dont you will learn by the pocket of money?

 

[john_the_great]

Has anyone found jets for the cns?

 

[wildemere]

You will not need any jets unless you live at 3000 feet.

Just the ability to read a manual, following the steps to tune it.

The main jet in mine was fine, just wrong everywhere else.

 

[skjjoe]

what manual?.please post

 

[wildemere]

Google

"two stroke tuning"

You will get about 1,000,000+ links

narrowing down to 2 stroke carb tuning will give about 200,000 hits

 

[skjjoe]

ohh the way your post sounded i thought your carb came with a manual

 

[john_the_great]

You will not need any jets unless you live at 3000 feet.

Just the ability to read a manual, following the steps to tune it.

The main jet in mine was fine, just wrong everywhere else.

I don't mean to be an @$$hole but you're wrong, on a motorcycle, a car, a moped etc, to get it to run at peak efficiency you need to re-jet it every time you install an aftermarket air filter, change the exhaust pipe, port the engine. There is only so much tuning you can do on a carb that is not jetted right. My engine has a tuned pipe, and I am planning on getting a uni air filter and match porting it, which will completely change the jetting.

 

[Venice Motor Bikes]

I don't mean to be an @$$hole but you're wrong, on a motorcycle, a car, a moped etc, to get it to run at peak efficiency you need to re-jet it every time you install an aftermarket air filter, change the exhaust pipe, port the engine. There is only so much tuning you can do on a carb that is not jetted right. My engine has a tuned pipe, and I am planning on getting a uni air filter and match porting it, which will completely change the jetting.

I agree!! Just because he got lucky with his jet, doesn't mean anyone else will! (Then they'll be stuck with having to jet & tune a carb that's 5-times more complicated!)

Note to all... Learn how to properly tune your stock carb first! Then if you still feel you want a better carb, you'll have a better idea of how to tune it.

 

[bairdco]

one thing someone should clear up (i guess i'll do it) is this is NOT a "bolt it on and go" carb.

like every aftermarket carb made, it'll require tuning. tuning requires patience. it also requires knowledge of what you're trying to do.

if you don't understand how a carb works and you think "gas goes in, speed comes out," then you should read up on things like "Venturi Effect" and "Fuel Atomization" and here's a basic link i just found: Dan's Motorcycle Carburator theory and Tuning that explains some basics pretty well.

i also want to point out that i have never owned a CNS carb, probably never will, and don't really care if you get one or not.

(edit) if you read this and thought "man, that bairdco guy really needs to get knocked down a peg or two, that cocky bast#$@," well, i just walked into the garage and there's a big puddle of fuel underneath my bike, thanks to my stock, never had problems with, NT carb. guess i'm rebuilding instead of riding for awhile...)