CNS carb problems
- Thread starter AlexHough
- Start date
Dave31
Active Member
I just finished trouble shooting my cns yd carb. Here is what I discovered. Once you have removed drained and disassembled the bowl off the bottom of the carb clean the internal surfaces untill they are free of gas. Now with the carb upside down and float resting on the gas inlet needle valve the bottom of the float pontoons should be level with the bottom of the main jet. If not properly adjusted (mine was way too low) push out the pivot pin to free the float assembly and adjust the tang that contacts the needle valve to suit. Now, while you have the float bowl off blow through the little plastic tube that comes off the bottom. Does any air come out of the brass tube that sticks up in the bowl ? This the vent pipe for the carb and mine was blocked. With it blocked the carb will not function properly. If yours is blocked carefully drill down through the brass vent pipe with a small drill bit (I used a 3/64 bit in a pin vise). Once you open the hole at the top of the tube slightly find the bootom of the tube and drill through the bottom to the hole below (where the plastic tube attaches). At this point you may want turn your attention to the main jet. I think it is too small. Unscrew it and drill it little larger with a #69 drill bit (.0292in) held in a pin vise. Both the bit and pin vise can be purchased in a model hobby shop. With these three adjustments to my carb it now works well and responds the way you would expect. Good luck Bill
Jumpa
New Member
Did or do you notice any difference from the stock carb "I know I would probably say yes even if it didn't , so all that work wouldn't seem in vain . So please answer me with an honest unbiased opinion if possible
Seems all this is for a carb that costs double the factory carb and does very little if anything as to improve performance. One came on my new Sky Hawk and I don't see any improvement at all in fact it runs like **** & I pulled it off and put on a spare stock one I had laying around. Right away ran fine. I can do with out the extra 1/2 M.P.H. if it takes all that to get it working right. Don't get me wrong I love tinkering and maintaining stuff as much as the next guy .. If we didn't we wouldn't have these bikes to begin with . However, if I gotta tool it right out of the box it goes back in the box. In fact if anyone wants it let me know used one day! Not even one day!.
No holes drilled in it has the choke lever and everything !
Or who wants to barter for a rear rim 2" heavy duty w/sprocket on it My fat ass keep warping them & @ 6'5" 290 lbs I guess I should expect it huh?
Last edited:
Hi, first let me say that what I did was not to improve on a stock performance standard. I did the modification work to solve what in my case was a quality control issue. My carb was faulty from the factory. I am not convinced that the work turned a good carb better, it just made a bad carb functional. As for the performance the the bike luggs my 285 pounds at up to 26mph (respectable but hardly breathtaking). If your happy with your current performance don't go through the agony. If you want better performance buy some other high perfomance carb. good luck, Bill
SdCruizer
New Member
the carb rocks
sure mine didnt work either the first time but from the little I know about carbs it was too rich
so I soldered the jet and drilled a smaller hole until I found the size that works
most here say it comes too lean, well mine was the opposite
once I figured that out it pulls better then stock, around the same top speed but I needed the extra pull it does, and I have solid proof of that claim using a cen clutch no chattering from a dead stop unlike the stock carb would do
thats the only proof I can measure though I use gps for top speed and its the same
I would invest in a set of micro drill bits and either upjet or downjet one size at a time until it seems to work
You can buy jets but they are expensive
here is a video I did just yesterday showing it works and idles great
believe me I was also very disappointed when I first received it and gave up. Only messed with it because I had nothing to do. Glad I did.
http://www.youtube.com/watch?v=MYZ0nCc62GU
I know little about carbs, only how to replace the parts on them. And the basics of how they work. So that may have helped me figure the jetting easier then someone with no idea what to do. You could always take that info to a small engine repair shop and they could help get it running too, not much to it
sure mine didnt work either the first time but from the little I know about carbs it was too rich
so I soldered the jet and drilled a smaller hole until I found the size that works
most here say it comes too lean, well mine was the opposite
once I figured that out it pulls better then stock, around the same top speed but I needed the extra pull it does, and I have solid proof of that claim using a cen clutch no chattering from a dead stop unlike the stock carb would do
thats the only proof I can measure though I use gps for top speed and its the same
I would invest in a set of micro drill bits and either upjet or downjet one size at a time until it seems to work
You can buy jets but they are expensive
here is a video I did just yesterday showing it works and idles great
believe me I was also very disappointed when I first received it and gave up. Only messed with it because I had nothing to do. Glad I did.
http://www.youtube.com/watch?v=MYZ0nCc62GU
I know little about carbs, only how to replace the parts on them. And the basics of how they work. So that may have helped me figure the jetting easier then someone with no idea what to do. You could always take that info to a small engine repair shop and they could help get it running too, not much to it
nightcruiser
New Member
My guess is you need to do a float adjustment, specially of your carb is not sitting completely level. If the float is letting too much fuel into the bowl on a CNS carb it will run helplessly rich....
I wrote a long-ish thread about tuning my CNS carb when I did it, you can read it here, there's lots of stuff there that might be helpfully to you...
http://motorbicycling.com/showthread.php?t=32736&highlight=cns+carb+working+great
As for the CNS being better than a standard carb, it is definitely more complex, running 3 jets compared to the standard carbs single jet. I dont have an NT carb to compare to, but I know my CNS carb is performing very well and my bike definitely pushes the limits of performance of one of these small two strokes. The CNS performed like crap at first (mine is not mounted completely level) and was a bit frustrating while I was learning about it and tuning it, but now that I have learned how it functions and got it tuned up right I am very happy with it.
The_Aleman
Active Member
I had a CNS v1 for several years and I got better power with it than the NT. It's much more tuneable, especially with the homemeade boost bottle I ran for awhile. Can't say much about the CNS v2.
Greg58
Well-Known Member
I have two bikes, one with the cns the other with the nt. the bike with the cns is much faster from start to topend. I'm still tuning on the nt trying to get it to run as close as i can to the cns.
http://motorbicycling.com/album.php?albumid=259&pictureid=3773
http://motorbicycling.com/album.php?albumid=259&pictureid=3773
The_Aleman
Active Member
I had 5 engines, all of em were straightplugs. Never had to rejet, they always were proper out of the box. Tested from 100 feet to 4400.
The NT is definitely the more painless of the carbs. It's a great all-around carburetor if you don't want to fine-tune anything.
The NT is definitely the more painless of the carbs. It's a great all-around carburetor if you don't want to fine-tune anything.