having allot of trouble with the cns carb, long story short, it seems to work when the air filter is off then when i put it back on it runs terrible, and on the one website it says to leave all the holes open except put a tube on the bottom one but when I got the carb the hose went from the top to the bottom and thats how everyone else's is. I've never got this thing to run good yet
Cns
- Thread starter Fuji Moto
- Start date
At first I just needed more power to get me up hills now I think its the motor and a new carb wont help. I still want one of theses if I ever get a good motor to bolt it up to.
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It sounds line the air filter is acting like the choke is on,,,,the holes in the airfilter need to add up to the size or more of the carb intake hole,and the filter needs to be held away from the carb intake hole with a raized(against the carb. side)screen,so it can get air from the whole filter beacause the filter restricts air flow also,,,,, The thing needs to breathe
It still wont even run right with it off actually, you think the filter that came with it would be suitable (blue one) it does seem to run ok when i shut the gas off and the carb drains out a bit or something i can get it to wind out nicely (till it runs out of gas ) no idea whats going on, sometimes with the gas on it will run ok for a few seconds at full throttle then out of nowhere bog down rev back up a bit all while the throttle is wide open sputters and carrys on, i checked everything i could the only other thing im not sure of is my spark like i said before the wires are only threads coming out of the cdi i rigged it back together, but that doesnt make any sense because it would run perfect with the gas off, 
huh, i did take the carb apart (its brand new) and looked it over a bit, how would this happen, has it happened before? how would i fix this if it is the problem? i am going to switch to the stock carb once i buy another used kit off someone else then i can troubleshoot further , thanks for the help!
I've been using the CNS carb for about 3 months on a skyhawk 48cc slant head.Some say the bottom hose is a vent and leave open.And that if you leave hooked to top it creates a suction from carb bowl.,.When I got the carb it had a piece of flimsy pink hose connected from top to bottom.I noticed that it was crimping.Went to hardware store and got a 1/8" ID plastic hose with a heavier wall,did'nt crimp.Then turned air/fuel screw all the way in and backed out 1 1/2 turns.It ran great but would'nt idle.Then adjusted idle screw,still would'nt idle.Took off carb and noticed an O-ring in throat off carb that will slip over manifold if I twisted and pushed on hard enough.That solved the idle problem.On this bike I've noticed I have to let it warm up maybe 3 minutes before it will run right.I do notice fuel going from bottom to top when accelarating.The top port that hose goes on goes directly into carb throat just ahead of the air filter.So it runs and feels like it's giving a boost of fuel when you open throttle.It looks to me if the top port is left open it's just extra unfilterd air going through carb.This is just my experiance with this carb on this engine.May help,may not on,your setup.
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The CNS is an old style Mikuni clone, it has 5 fuel metering circuits and requires a step by step method to tune properly. Its a trial and error process that requires patience and a good
understanding of the fuel circuits and their effect on the engine.
The hoses attached to it are air vents except for the top and bottom ones, the top one is a oil injection fitting that the chinese decided to attach to the fuel bowl overflow. This should show no fuel flow unless the float is set high. In a old school road bike or off road motorcycle application the bottom port is a hose run to the ground (overflow) and the top port is connected to the oil pump. The other two are plumbed to the clean side of the air box or fitted with tiny foam filters.
http://www.mikuni.com/pdf/vmmanual.pdf
The stock HT carb is easy to setup, their is only really 2 tune-up options, main jet and needle clip, Unless you start adjusting the slide cutaway or needle taper.
In a real carb like the CNS the fuel circuits overlap and must be tuned to work together. When setup properly the difference is awesome. Crisp idle, solid midrange and a cool running WOT.
Even better results can be gained from a real 16 to 19mm Mikuni or Delorto since the CNS is a crappy clone with loose tolerances.
New CNS owners should do the trial and error stuff on the stock carb, try different main jet sizes, clip positions, plug readings engine responce ect. then when confident move on to the more complicated setup.
Good things to know about using CNS or similar carbs.
The cable operated choke circiut has no effect on air flow and is a great tune up tool, a lean or rich setting can be verified by your handlebar mounted choke application.
4 stroking can happen when lean as well, bump the choke and see.
Air screw adjustments slightly affect the full RPM range so allow for weather/conditional running.
I have set up my CNS for lean idle, crisp midrange running and use the "choke" for extra fuel for high revs and hills.
"Fuel is the main coolant for two strokes". Gordon Jennings
These HT's love a rich WOT.
understanding of the fuel circuits and their effect on the engine.
The hoses attached to it are air vents except for the top and bottom ones, the top one is a oil injection fitting that the chinese decided to attach to the fuel bowl overflow. This should show no fuel flow unless the float is set high. In a old school road bike or off road motorcycle application the bottom port is a hose run to the ground (overflow) and the top port is connected to the oil pump. The other two are plumbed to the clean side of the air box or fitted with tiny foam filters.
http://www.mikuni.com/pdf/vmmanual.pdf
The stock HT carb is easy to setup, their is only really 2 tune-up options, main jet and needle clip, Unless you start adjusting the slide cutaway or needle taper.
In a real carb like the CNS the fuel circuits overlap and must be tuned to work together. When setup properly the difference is awesome. Crisp idle, solid midrange and a cool running WOT.
Even better results can be gained from a real 16 to 19mm Mikuni or Delorto since the CNS is a crappy clone with loose tolerances.
New CNS owners should do the trial and error stuff on the stock carb, try different main jet sizes, clip positions, plug readings engine responce ect. then when confident move on to the more complicated setup.
Good things to know about using CNS or similar carbs.
The cable operated choke circiut has no effect on air flow and is a great tune up tool, a lean or rich setting can be verified by your handlebar mounted choke application.
4 stroking can happen when lean as well, bump the choke and see.
Air screw adjustments slightly affect the full RPM range so allow for weather/conditional running.
I have set up my CNS for lean idle, crisp midrange running and use the "choke" for extra fuel for high revs and hills.
"Fuel is the main coolant for two strokes". Gordon Jennings
These HT's love a rich WOT.
