Carby cns carb questions please

[Gumby3624]

Hi, I have a raw 48 cc engine, purchased a cns carb, (later asked place where I bought it from how to tweek the idle and air/fuel set screws because there were no intructions with the carb, and they told me that carb was not meant for my engine). Just so you know, I broke the engine in by the book. Went 200+ miles between 15 and 18 mph, never more than 30 min run time and punched it a few times for hard short stresses to help. Any way my question is, I understand the idle screw (front), now the fuel/air mix screw, all the way in (clockwise) is highest fuel to air mix? I don't understand why they say it is not meant for this engine because I have more low end torque than before, and from 18 to 22 mph it's like the engine has twice the power than it did before. The only difference is that before I could reach 28 mph and now I can only get to 25 mph. (one other thing, I replaced the plug with a ngk br7-hs instead of the stock b-6l. I know that the 6 is a hotter plug, could this have made the difference? Will this in any way damage my engine? The plug looks fine, not lean at all. If this is what I have to live with, that's ok. I do know that when I took off the filter I noticed unused fuel in the carb, is this normal? Any help would be appreciated

 

[Gumby3624]

ok, I see I've had 30 hits, except no replies...does that mean no one is familiar with the cns carb?

 

[bigdan]

Well, one reason you may not have any replies is the subject of your post. People don't like posts with ambiguous subjects."cns carb questions please" That doesn't really tell you what the post is about other than it involves a CNS carb. A better subject would be "Can you use the CNS carb with a raw 48cc engine" because that is the subject of your post.

But to answer your first question: The CNS carb is designed for a 80cc engine. You may be able to find a jet kit for the CNS carb. But you'll definitely need to tune the carb to run on your engine.

It sounds like you have the bottom end tuned properly but the top end isn't getting the right air:fuel ratio which is why you've lost power at the top end. You could try adjusting the height of the C clip on the slide needle. This will change the low to mid range and then you would readjust the air:fuel screw. But, I think you'll need to rejet the carb.

There is one other option. If you can't find a jet kit, fill the hole in the jet with solder and then drill it out to a smaller sizer. If you search the forums, there's posts on how to do that.

 

[Gumby3624]

thanks for the reply!

You're right I guess I wasn't specific enough with my inquiry heading. I appreciate the help you've given me. My question now is, if I am not worried about the top end, is this carb ok to use. The vendor I bought it from said not to use it at all. I am satisfied with what I have now, are there any issues I should be worried about, will it be detrimental to my engines life span?
Tim

 

[Gumby3624]

oh one other thing please

the vendor that sold me the cns has not told me if turning the set screw on the air fuel ratio totally clockwise is less fuel or more fuel. Any help would be greatly appreciated in tweekin this carb! Thanks again

 

[beetlefarm68]

I have a racing (lol) cns carb I have found some jets that are Dellorto PHVA PHBL 6mm Main Jets for $2.88 each plus cheap shipping will this work and what sizes should i order thanks http://www.1977mopeds.com/parts/carburetion/dellorto-parts/dellorto-main-jet-sha-phbg-2730.html

 

[kilzo90]

help!!

help ill been playing with my SkyHawk CNS High Performance Carburetor II for hours now i got it to idle pretty good and it takes off only when im at about 1/4th throttle any thing past that i dont have any thing at all it wants to do it die or bog out! if im nice on the throttle only at 1/4 the bike will go about 15mgh keep in mind i have a skyhawk gt5 66cc i have used automotive silicone to seal off my magneto from water and the cap where the cables go into the carb there should not be any air leak on it i just cant fig it out for the life of me

 

[HeadSmess]

here we go again

a carb is simple.

a tube with a tiny tube at right angles, opening up inside it.

air passes through the main tube and passes the end of the smaller tube.

this small tube experiences a pressure drop.

it is called a "venturi"

it is how a spraygun works, and how a carburettor works. old insecticide sprays (think 1960 mortein) also work the same. old style perfume sprays. etc.

a certain diameter tube will only flow so much air at such a speed.

the pressure drop is proportional to the airspeed.

by adjusting the size of the small tube, we can adjust how much material is "sucked" through it. (really it is pushed through it by the surrounding atmosphere being at a higher pressure than that inside the tube or carbthroat).

there you go.


80cc has same size intake as 48cc.

other than tweaking jets it is the same carb. same throat bore, same carb. the 48 will have smaller jets cus it moves less air per revolution, and correspondingly needs less fuel at the same RPM.

alternatives are.

buy jets, from .45 to .65, depending on altitude (get a .40 if your up in the himalayas).

buy some number drills, and solder. start big and work down. lot of work, i know.

get some super thin copper wire and tack one strand in at a time to the jet. dont fill it with solder, just one strand of wire at a time.


read some books on jetting, heaps of info, doesnt matter what brand carb it is, basics are the same. two tubes, one adjusts airflow, one adjusts fuel flow... learn to read the engine sound, plug and exhaust.

the "air screw" can be an air screw or a fuel screw depending on brand. one richens when tightened, the other leans when tightened. trial and error will reveal what you have!

 

[HeadSmess]

here we go again

a carb is simple.

a tube with a tiny tube at right angles, opening up inside it.

air passes through the main tube and passes the end of the smaller tube.

this small tube experiences a pressure drop.

it is called a "venturi"

it is how a spraygun works, and how a carburettor works. old insecticide sprays (think 1960 mortein) also work the same. old style perfume sprays. etc.

a certain diameter tube will only flow so much air at such a speed.

the pressure drop is proportional to the airspeed.

by adjusting the size of the small tube, we can adjust how much material is "sucked" through it. (really it is pushed through it by the surrounding atmosphere being at a higher pressure than that inside the tube or carbthroat).

there you go.


80cc has same size intake as 48cc.

other than tweaking jets it is the same carb. same throat bore, same carb. the 48 will have smaller jets cus it moves less air per revolution, and correspondingly needs less fuel at the same RPM.

alternatives are.

buy jets, from .45 to .65, depending on altitude (get a .40 if your up in the himalayas).

buy some number drills, and solder. start big and work down. lot of work, i know.

get some super thin copper wire and tack one strand in at a time to the jet. dont fill it with solder, just one strand of wire at a time.


read some books on jetting, heaps of info, doesnt matter what brand carb it is, basics are the same. two tubes, one adjusts airflow, one adjusts fuel flow... learn to read the engine sound, plug and exhaust.

the "air screw" can be an air screw or a fuel screw depending on brand. one richens when tightened, the other leans when tightened. trial and error will reveal what you have!

 

[kilzo90]

i know the basic understanding of a carb just need a little help with it!

let me try this again the bike will idle nice but the min i put any kind of throttle on it it dies or bogs out to the point it wants to die, My old carb works i switched the jets and used the flowt out of it to because i already had that set so it wasnt too low and that it wasnt over flowing what else can i do about it?i live in mn so it just get kind of humid up here iv been playing around with it for like 4-5 days now i have even tried using silicon so there wasnt any kind of air leak and it does the same so i cleaned it back up any ideas?