how do you properly tune cns carb?

[alienboy366]

my idle is preety whack. sometimes its real high, sometimes it dies. have no idea how to properly tune it. my clip is second from bottom gets good power mid range, ehh power high range but cruddy power on the bottom end and crapy idle. can anyone help?

 

[oldguy387]

Search this site a little more and you will find some great posts about this subject.

 

[Nikko]

Search this site a little more and you will find some great posts about this subject.

instead of telling him to look harder why dont you just give your input on the question. alot of the time the search doesnt do much good because you only find posts with one word or 2 that you searched and has nothing to do with what your asking.

and i cant help you man.

 

[decoherence]

ha ha ha. hypocrisy!


for the cns, on the side are two screws.
one is your mixture & the other is idle speed.
if you look around or search, there is some good threads going on about tuning them.
if the engine isn't broken in yet, it might be hard to get the engine perfect. especially if the engine is not warmed up yet.
after breaking in, continued tweaking will be needed.

 

[nightcruiser]

I recently made a series of posts about how I tuned my CNS carb to run really great, here is a link to that thread.
http://motorbicycling.com/f4/cns-carb-working-great-32736.html
As for your idle going up and down, couple things could be at play here.
1) the clutch could be putting a drag on the engine and killing it. This drag could be a bit variable, for instance, when you rotate the handlebars the clutch cable may tighten or loosen just a tiny bit causing more or less drag. This can be responsible for the change in idle speed. If you are having a hard time getting the clutch adjusted properly check the nut on the drive sprocket to be sure it's tight, that nut pulls in the internal spring on the clutch. If that nut is not fully seated the spring is not compressed enough and the clutch will require too much travel to operate properly with the clutch lever.
2) Similarly, if your throttle cable has any sharp bends it may be hanging up a bit and not returning to the home position all the way. Turn the handlebars, see if the idle changes, wiggle the throttle cable where it goes into the carb also to see if this is a source of problem.
3) You could have air leaks in your carb, where the carb mates with the intake, where the intake mates to the engine, or at the exhaust. Air leaks would cause a motor to run erratic.

I commend you on your choice to move the needle downward, that was the right decision which is confirmed by your improved mid throttle response. Read through my thread linked above to see what I had to do to fix the rest of the throttle range....

 

[mpsmall]

i had crappy low end power also... i jetted my main jet to make it run richer and have the needle set right in the middle. Now i get decent low end and still have a great high end also.

 

[rustycase]

alien, the cns carbs are a LOT of fun.
You shall see, when you begin a few days worth of reviewing the posts about them.
With a lot of faith you shall overcome the little rascal and triumph, in the end.

NOW, I agree with all those who advised I purchase an NT carby, which will still need to be re-jetted for suitable performance. In the end, it's a better, and simpler carb.

MY 2 cents.
...and my cns still ain't right !
rc

 

[IreBo]

I agree, the nt carb is much more reliable but not a hot rod carb. i orderd a gen 1 cns and it worked for a few miles and then sterted to rev irraticly, and did not want to idle. it hit the high rpms ok but was a joke at idle and mid. i took it off and replaced it with the stock nt and ran great. i still have it on their but look foward to a Dellorto. i took the carb apart removed the jets and stuff. it had a bunch of metal shaveings in it and some holes wer restricted. im guessing that was the problem. i cleaned it, reassembled and have yet to try it.....