Cns carb adjustment clarifications

GoldenMotor.com
H

husamwadi

New Member
Jun 7, 2009
6
0
0
Cape Girardeau
Cns carburetor adjustment/screws??

Hi, I'm having some issues with my CNS Carb.


Specs:

Jet 80cc 2 Stroke Bicycle Motor -Jet 80cc 2 Stroke Bicycle Engine Kit

GRUBEE SkyHawk GT5 66cc/80cc Slant Head Bike Motor Kit (Standard Finish)
Standard Finish
2.75 HP. - Speed depends on rear sprocket ratio and weight of rider, weight of bike, the climate and the terrain being ridden.
Magneto With Solid State New Design Capacitive Discharge (CD) Ignition
44-Tooth, 9 Hole Chrome Sprocket
New EPA Approved Black Cat Muffler with Heat Shield
Push Button Clutch Lever And Cable
New EPA approved high performance fuel line
Improved Gas Valve
New High Performance Gen B Carburetor ($65 value)
Chrome Lined Cylinder Wall
Head With 45 Degree Angle Fire Spark Plug


Anyway, I need clarification on how to adjust the idle screws, WHICH WAY TO TURN, and why the idle turns off when i put the choke all the way up?

VIDEO OF QUESTIONS:

CNS CARBURETOR QUESTIONS - YouTube

*ADDED QUESTION*
I'm running a 44 tooth rear sprocket, and Im getting to around 35mph, any more than that and the engine roars (high rpms) but loses power?
Should I get a smaller gear for higher power, and will a smaller gear stop the high rpms?

:-||
 
Last edited:
N

nightcruiser

New Member
Mar 25, 2011
1,180
2
0
USA
Hey, no worries, seems like you got lucky if your bike will idle with the CNS carb straight out of the box!
The "choke" is confusing, I had all the same questions as you. First off, its NOT a choke! It is an "enrichment circuit" that opens up an extra fuel jet and small air passage when you pull on that cable. So, no pull/no "choke", full pull/full "choke". What is happening here is that plunger in the carb is pushed down by the spring and closing the extra fuel and air off, when you pull the cable the plunger rises and opens them up. I had to take apart the carb and examine it, blow through passages etc to figure out what was really going on here.
My experience with the "choke" is since it adds more fuel to the mix it can have a huge range of effects on how your motor runs, depending on how the carb is tuned. For instance, if your too lean pulling the "choke" cable adds gas and can make the idle speed up, or make an engine that wont idle idle. On the other hand, if you are running rich or just right, pulling the "choke" adds gas and can make the mix too rich and cause a stall (slight flooding). This sounds like your scenario.
I have been around the bend tuning this CNS carb and have seen so many different conditions, I finally got mine running nice. I am no expert mechanic so I don't know that it's adjusted "right, but my bike idles great and has solid pull through the entire throttle range, top speeds so far around 35MPH, plug is a nice medium brown color...
Since my carb has been tuned and running nice I use the "choke" for about the first 15 seconds of the ride. I find from a cold engine she will start without the choke but runs rough for a short while, pulling the "choke" kicks her to life at that point, a few seconds later I release the "choke". The improvement in the smoothness of a cold engine is very noticeable when you pull the choke. Like you, my bike will not idle with the choke pulled, but it doesn't need to since the choke is only pulled for that initial moment when the engine is cold, when the choke is released the engine idles nicely. I am guessing you are in a warm climate, in that case you might not need the choke at all.
On the adjustment screws... The idle speed screw actually pushes up on a wedge on the slide in the carb, preventing it from closing all the way down. You should pull the throttle a bit when you tighten this screw to prevent gauging the contact point on the slide. Tightening the screw more keeps the slide up more, makes the engine idle higher. Tightening the air screw reduces air supply. You should set your idle screw first, then start with the air screw about 1 turn out from tight (never "tighten" these screws, just seat them). With the engine idling, back out the air screw about 1/4 turn at a time until you achieve the fastest idles speed.
How does she run otherwise? Do you have good pull through the throttle range and good top end?
 
H

husamwadi

New Member
Jun 7, 2009
6
0
0
Cape Girardeau
THANK GOD! your like a miracle from heaven lol.

anyway, thanks for answering my questions, so here's the low down:

My bike was running like a charm, hitting speeds of 35mph out of the box, no troubles at all. But, when I wanted to go faster, The engine would rev like crazy (4 stroking i guess) and the whole bike would vibrate like it was gunna fall apart. So, with me and my stupidity I decided to mess around with the "adjustment screws", and of course I forgot what the original settings were :/ . Now the bike runs weird, it'll start up and the engine KICKS the bike every time the piston moves, but once I pull the choke thing up it seems to run kinda fine, just not as fast as it used to.

Now, another question to make sure, when you turn the screw, what exactly is a full turn?: brnot
 

Attachments

N

nightcruiser

New Member
Mar 25, 2011
1,180
2
0
USA
A full turn is 360 degrees....
The two screws on the outside of the carb are going to effect the idle, thats it, they are not going to have effect on the top end speed of the bike. If you have lost top end speed and performance then I would suggest you make sure you haven't developed any air leaks (at carb throat, at intake gasket, at exhaust gasket, on head). You should also check the air filter, sometimes it can get soaked in fuel/oil and choke off the air, dry it out by pressing between some dry towel.
And congratulations, you are the first person that has reported their CNS carb running great right out of the box, good idle and top end speed of 35MPH is great, you should be satisfied with that (for now) and break in your motor. After she is broken in you will get an inprovemnt in smoothness and horsepower, it will take around 500-800 miles of riding to break her in....
Have fun
 
S

sexy beast

New Member
Aug 10, 2013
2
0
0
Tucson az
My cns high performance carburetor has an idle adjust screw but no air intake adjust screw? I have no clue why and it won't run at all it just floods my engine.. anyone have this problem? Or is it not a problem and I just suck with carbs?:-||
 
N

nightcruiser

New Member
Mar 25, 2011
1,180
2
0
USA
sexy beast said:
My cns high performance carburetor has an idle adjust screw but no air intake adjust screw? I have no clue why and it won't run at all it just floods my engine.. anyone have this problem? Or is it not a problem and I just suck with carbs?:-||
Click to expand...
Adjust the float to lower the fuel level in the carb bowl...

The mix screw is under the brass cap, drill/pry it off and there it is...
 
jpullen

jpullen

New Member
Sep 18, 2013
27
0
0
Damascus GA.
I hate to beat the dead cns horse but I just want to know if mine is acting correctly. I am r on my first tank of gas on my first build. I have the cns idling nicely after using the information from this thread. It accelerate well without bogging (I don't go over 15mph because of breaking it in) but when I rev it wants to bog for a few seconds ( not really an issue). I had to set the rpm screw really high to get it to idle though and when I turn off the gas to run it out of the carb it revs super high and sounds like it might throw a rod. Is my float to high or am I just nit picking? Oh it also eats gas like crazy but not coming out the overflow tube other than a drop here or there.
 
crassius

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
CNS carbs aren't my specialty, but a new engine may get as little as 20 miles per gallon at the beginning of the break-in period - by 3rd or 4th tank, it may be up to 50 or 70 per gallon
 
jpullen

jpullen

New Member
Sep 18, 2013
27
0
0
Damascus GA.
Thanks I had forgotten about early break in mpg, but what about excessively big rev when gas runs low in the bowl is tat normal?i
 
JUGGALO

JUGGALO

New Member
Sep 25, 2013
4
0
0
Marinette, Wi
I need some help tuning my carb. Ive tried everthing i can think of but its still kinda crappie. And my spark plug is all black and grittie. Im open to any and all ideas. Some one plz hit me back in this.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
jpullen said:
I hate to beat the dead cns horse but I just want to know if mine is acting correctly. I am r on my first tank of gas on my first build. I have the cns idling nicely after using the information from this thread. It accelerate well without bogging (I don't go over 15mph because of breaking it in) but when I rev it wants to bog for a few seconds ( not really an issue). I had to set the rpm screw really high to get it to idle though and when I turn off the gas to run it out of the carb it revs super high and sounds like it might throw a rod. Is my float to high or am I just nit picking? Oh it also eats gas like crazy but not coming out the overflow tube other than a drop here or there.
Click to expand...
If your engine revs higher when you shut off the fuel, your jetting is too rich. Try leaning the mixture a bit at a time until it just revs a little before it dies when you run it dry. Keep a close eye on the plug while adjusting it. Search "plug chop" for tuning help too.
I'm not a cns fan so I have no clue how to lean them, sorry.
 
R

Richie rocket 72

New Member
Sep 24, 2018
13
1
1
52
nightcruiser said:
Hey, no worries, seems like you got lucky if your bike will idle with the CNS carb straight out of the box!
The "choke" is confusing, I had all the same questions as you. First off, its NOT a choke! It is an "enrichment circuit" that opens up an extra fuel jet and small air passage when you pull on that cable. So, no pull/no "choke", full pull/full "choke". What is happening here is that plunger in the carb is pushed down by the spring and closing the extra fuel and air off, when you pull the cable the plunger rises and opens them up. I had to take apart the carb and examine it, blow through passages etc to figure out what was really going on here.
My experience with the "choke" is since it adds more fuel to the mix it can have a huge range of effects on how your motor runs, depending on how the carb is tuned. For instance, if your too lean pulling the "choke" cable adds gas and can make the idle speed up, or make an engine that wont idle idle. On the other hand, if you are running rich or just right, pulling the "choke" adds gas and can make the mix too rich and cause a stall (slight flooding). This sounds like your scenario.
I have been around the bend tuning this CNS carb and have seen so many different conditions, I finally got mine running nice. I am no expert mechanic so I don't know that it's adjusted "right, but my bike idles great and has solid pull through the entire throttle range, top speeds so far around 35MPH, plug is a nice medium brown color...
Since my carb has been tuned and running nice I use the "choke" for about the first 15 seconds of the ride. I find from a cold engine she will start without the choke but runs rough for a short while, pulling the "choke" kicks her to life at that point, a few seconds later I release the "choke". The improvement in the smoothness of a cold engine is very noticeable when you pull the choke. Like you, my bike will not idle with the choke pulled, but it doesn't need to since the choke is only pulled for that initial moment when the engine is cold, when the choke is released the engine idles nicely. I am guessing you are in a warm climate, in that case you might not need the choke at all.
On the adjustment screws... The idle speed screw actually pushes up on a wedge on the slide in the carb, preventing it from closing all the way down. You should pull the throttle a bit when you tighten this screw to prevent gauging the contact point on the slide. Tightening the screw more keeps the slide up more, makes the engine idle higher. Tightening the air screw reduces air supply. You should set your idle screw first, then start with the air screw about 1 turn out from tight (never "tighten" these screws, just seat them). With the engine idling, back out the air screw about 1/4 turn at a time until you achieve the fastest idles speed.
How does she run otherwise? Do you have good pull through the throttle range and good top end?
Click to expand...
I have a few questions I have the motorized bike I bought the expansion chamber the high compression head the CNS Carburetor that I'm not certain if I got working correctly at all and the 36 tooth sprocket as I understand I'm supposed to go nearly 50 miles an hour and I'm not going anywhere near that
 
R

Richie rocket 72

New Member
Sep 24, 2018
13
1
1
52
nightcruiser said:
Hey, no worries, seems like you got lucky if your bike will idle with the CNS carb straight out of the box!
The "choke" is confusing, I had all the same questions as you. First off, its NOT a choke! It is an "enrichment circuit" that opens up an extra fuel jet and small air passage when you pull on that cable. So, no pull/no "choke", full pull/full "choke". What is happening here is that plunger in the carb is pushed down by the spring and closing the extra fuel and air off, when you pull the cable the plunger rises and opens them up. I had to take apart the carb and examine it, blow through passages etc to figure out what was really going on here.
My experience with the "choke" is since it adds more fuel to the mix it can have a huge range of effects on how your motor runs, depending on how the carb is tuned. For instance, if your too lean pulling the "choke" cable adds gas and can make the idle speed up, or make an engine that wont idle idle. On the other hand, if you are running rich or just right, pulling the "choke" adds gas and can make the mix too rich and cause a stall (slight flooding). This sounds like your scenario.
I have been around the bend tuning this CNS carb and have seen so many different conditions, I finally got mine running nice. I am no expert mechanic so I don't know that it's adjusted "right, but my bike idles great and has solid pull through the entire throttle range, top speeds so far around 35MPH, plug is a nice medium brown color...
Since my carb has been tuned and running nice I use the "choke" for about the first 15 seconds of the ride. I find from a cold engine she will start without the choke but runs rough for a short while, pulling the "choke" kicks her to life at that point, a few seconds later I release the "choke". The improvement in the smoothness of a cold engine is very noticeable when you pull the choke. Like you, my bike will not idle with the choke pulled, but it doesn't need to since the choke is only pulled for that initial moment when the engine is cold, when the choke is released the engine idles nicely. I am guessing you are in a warm climate, in that case you might not need the choke at all.
On the adjustment screws... The idle speed screw actually pushes up on a wedge on the slide in the carb, preventing it from closing all the way down. You should pull the throttle a bit when you tighten this screw to prevent gauging the contact point on the slide. Tightening the screw more keeps the slide up more, makes the engine idle higher. Tightening the air screw reduces air supply. You should set your idle screw first, then start with the air screw about 1 turn out from tight (never "tighten" these screws, just seat them). With the engine idling, back out the air screw about 1/4 turn at a time until you achieve the fastest idles speed.
How does she run otherwise? Do you have good pull through the throttle range and good top end?
Click to expand...
Night Cruiser will you help me I'm very new to this I do have a CNS carb I did drill out the little cover for the air to fuel ratio screw I do not know when to use the choke or they added extra air flow I don't know what it's for but I don't know when to use it and I have high-performance Parts on my bike I have a compression chamber high compression chamber Muffler I have a high compression head I have the high-performance CNS Carburetor I have the 36 tooth sprocket have everything I need to make a bike faster although it won't go over 30 miles an hour why is this
 
xseler

xseler

Well-Known Member
Apr 14, 2013
2,886
151
63
OKC, OK
Richie rocket 72 said:
Night Cruiser will you help me I'm very new to this I do have a CNS carb I did drill out the little cover for the air to fuel ratio screw I do not know when to use the choke or they added extra air flow I don't know what it's for but I don't know when to use it and I have high-performance Parts on my bike I have a compression chamber high compression chamber Muffler I have a high compression head I have the high-performance CNS Carburetor I have the 36 tooth sprocket have everything I need to make a bike faster although it won't go over 30 miles an hour why is this
Click to expand...

I fought with the CNS carb for 3 or 4 years. Id' think it was good to go, then it wasn't. The best way to adjust this carb is to swap it with a lowly NT carb and then put a smaller jet in it. I've got a 36 tooth, expansion chamber, and a Fred head. Been clocked by traffic radar at 45mph. Make sure your brakes have been upgraded!!
 
R

Richie rocket 72

New Member
Sep 24, 2018
13
1
1
52
xseler said:
I fought with the CNS carb for 3 or 4 years. Id' think it was good to go, then it wasn't. The best way to adjust this carb is to swap it with a lowly NT carb and then put a smaller jet in it. I've got a 36 tooth, expansion chamber, and a Fred head. Been clocked by traffic radar at 45mph. Make sure your brakes have been upgraded!!
Click to expand...
I have an expansion chamber a high compression head a high-performance spark plug the CNS high performance carburetor as well as his 36 tooth sprocket and cannot break 30 miles an hour can you tell me why
 
xseler

xseler

Well-Known Member
Apr 14, 2013
2,886
151
63
OKC, OK
Richie rocket 72 said:
I have an expansion chamber a high compression head a high-performance spark plug the CNS high performance carburetor as well as his 36 tooth sprocket and cannot break 30 miles an hour can you tell me why
Click to expand...
I believe that I already did in the bold typeface.
 
Greg58

Greg58

Well-Known Member
May 1, 2011
5,353
2,575
113
65
Newnan,Georgia
Ritchie what was your top speed before the upgrades? Most stock engines will do around 34 to 35 after the break in. My 48cc with only slight modifications will do 30+ with a 44 tooth sprocket, my 66cc with same mods and the pipe I made will do 38 with a 41 tooth rear sprocket. I weigh about 210 lbs so a smaller sprocket doesn't work for me.
 
Greg58

Greg58

Well-Known Member
May 1, 2011
5,353
2,575
113
65
Newnan,Georgia
These little engines are not complicated but tunning is critical, you have to learn how to read a spark plug to get the carb jetted correctly . The problem with tunning the CNS is the carb never really seals to the intake causing air leaks that change the air to fuel mix, as X said the basic nt to me is a much simpler carb that serves well and fits the intake.
 
  • Like
Reactions: xseler
You must log in or register to reply here.
Top Bottom