OMG I have to tune a CNS!!! Help

[SdCruizer]

it looked really good until I sprayed degreaser all over
it dulled the silver
I could go over with sandpaper again to shine them back up

I used a dremmel with a cone sander bit, some micro files and emory cloth sand paper
its alot of work probably 2 hrs on the bike

 

[nightcruiser]

I'm kinda surprised you got a CNS carb from BGF, I had thought he was sending out the NT carb still... I guess maybe he ran out of that stock and had to get new kits with the CNS now. As far as it being "real", the CNS has been made in a few factories, with a few versions, they are all real....

On your idle issue, you might need to adjust your float a bit, I would say to lower the fuel level in the bowl. When I first built my bike I couldn't get idle, if I got her running and hit WOT she would scream but died when I backed down to idle. I found fuel was really pouring through the carb, ended up dripping from the muffler eventually. One day I started out a ride and forgot to turn on my fuel valve, low and behold after a short while the motor really livened up and I finally was able to get idle, then she died. Took only a moment to realize the fuel valve was off, when I turned it back on she was running the same again, good at WOT but no idle. So I turned off the fuel valve again, same thing happened, major improvement after some of the fuel in the bowl burned out and she now idles, then dies. This told me I needed to do a float adjustment and lower the fuel level in the bowl. After I did this I got great idle, from there I went on and jetted the carb to get good conditions at WOT and mid throttle range. I made a long-ish post about my experience with my CNS carb at the time, take a moment and read through it, I think you will find it helpful.... (I can't repeat all the stuff here)
http://motorbicycling.com/showthread.php?t=32736&highlight=cns+working+great

After my carb was tuned I find that she will start fine and idle without the choke, but before she is completely warm she will run a bit rough. If I pull the choke a bit at this point the power returns and she runs smoother, but usually dies at idle with the choke on. This has been no big deal because it usually takes about a 1 block ride with the choke on to warm the motor, before I let off the throttle I turn off the choke and she idles fine. After the short ride I never need the choke again...

 

[SdCruizer]

it idles great when warmed, its only cold like when I use the enricher it takes 3-4 min it wont idle at all but die

is that normal for this carb

when hot I can get it to idle so low it almost dies if I want to


if I remember I will make a video if it helps

 

[nightcruiser]

Every motor/carb is a bit different, all I can do is suggest you read through the thread I linked and apply what is written there to your particular situation.
Like I said earlier, on my bike on a day that is at least 60 degrees, it takes only about a block or two of riding with the choke before the motor is warmed up.....

 

[SdCruizer]

Ive read through it all in 1 week
this is the sum of all these posts
upjet, check needle, check float, adjust air screw

well I had to down jet came way to rich, im at sea level
adjusted needle leaner
float checked out correctly how it came,carb also sits dead level on the intake

no mention of what to do with the hoses, ive read capped, taken out from somewhere I cant remember
all I know is to have a hose on the bowl, and on the vent
the 2 other nipples I have no idea what to do

didnt really see much about idle im just surprised how bad it idles when cold
the stock carb barely needed choke for the first 10 seconds after that none

 

[biknut]

Ive read through it all in 1 week
this is the sum of all these posts
upjet, check needle, check float, adjust air screw

well I had to down jet came way to rich, im at sea level
adjusted needle leaner
float checked out correctly how it came,carb also sits dead level on the intake

no mention of what to do with the hoses, ive read capped, taken out from somewhere I cant remember
all I know is to have a hose on the bowl, and on the vent
the 2 other nipples I have no idea what to do

didnt really see much about idle im just surprised how bad it idles when cold
the stock carb barely needed choke for the first 10 seconds after that none

Normally bad idle when cold is a good sign. If your jetting is good when hot, your motor chould be too lean when cold. The motor gets richer as it warms up.

The NT carbs are usually rich out of the box.

 

[SdCruizer]

so its just the coldness of the engine keeping it from idling correctly?
I know the stock carb was a hair richer because it did idle great cold

maybe im used to electric chokes that keep engines running the same cold or hot
guess my 2 stroke leaf blower does idle horribly when cold too

its just confusing going from great idle cold stock carb, to crap idle cold new carb
just wanted to see if thats common

I usually start mine on a jackstand and let the warm up always when at home. Never ride when they are cold

 

[Greg58]

Biknut, sorry I was not clear on my jet size. Mine is at a #64 drill bit, I drilled it out with a 69 first then one size larger till I got the plug color that I wanted. With a stock air filter and the restrictive air flow the 69 was fairly good.

 

[nightcruiser]

I said read through what is posted and apply what you learn to YOUR situation. If you're running rich then maybe you need to down jet, most of us have needed to up jet. Then again, if you were to adjust the float a little bit you might not be running rich any more and might not need to down jet either. And BTW, the size of the main jet isnt what is responsible for setting the mix at idle, that would be the idle jet, idle screw, and the float setting has a large influence as well....
On the hoses, there are several versions of the CNS carb and not all of them have the same hoses. On the ones with the stock red plastic air filter the top one goes into the air filter, on your version those hoses can be left open or you can plug them. Some people have better luck plugging them, others leaving them open, some like to be connected to the air filter, its trial and error. The only one I wouldn't plug is the overflow that comes from the bottom of the carb.
Sorry we can't tell you exactly what to do with your carb, there are lots of factors that determine what adjustments need be made...
I still say you might want to play with the float adjustment a little bit. Try this, next time you start out cold, turn on the fuel valve, start the motor, turn off the fuel valve and warm it up as normal. See if it seems to hold idle better (warm up quicker) before it dies. If so, you could benefit from a float adjustment.

 

[porch lizard]

Thanks for going over all this info guys. I'm getting close to starting up my second MaB build, and just when I thought I knew how to tune the CNS carb, this second engine came with an updated CNS carb that has the extra hoses, and no needle slots to adjust the mixture with. I hope it all goes smoothly and I get it right without too much messing around.

 

[nightcruiser]

Thanks for going over all this info guys. I'm getting close to starting up my second MaB build, and just when I thought I knew how to tune the CNS carb, this second engine came with an updated CNS carb that has the extra hoses, and no needle slots to adjust the mixture with. I hope it all goes smoothly and I get it right without too much messing around.

No needle slots, really? That sucks, I would order a rebuild kit and put an adjustable needle in there right away....

 

[porch lizard]

I'll give this one a try first, and keep my fingers crossed hoping it works right. The needle looks the same, but I didn't measure it so I don't know if the rebuild kit one would work or not. Its a good idea though, thanks for bringing it up.

 

[nightcruiser]

I'll give this one a try first, and keep my fingers crossed hoping it works right. The needle looks the same, but I didn't measure it so I don't know if the rebuild kit one would work or not. Its a good idea though, thanks for bringing it up.

Does this CNS have both idle adjust screw and the air screw, or just the idle screw? I guess the newest ones coming around are supposed to have the air mix screw capped off, I have been wondering how these newer CNS carbs are working out for people....

 

[rustycase]

Biknut, sorry I was not clear on my jet size. Mine is at a #64 drill bit, I drilled it out with a 69 first then one size larger till I got the plug color that I wanted. With a stock air filter and the restrictive air flow the 69 was fairly good.

I'm not clear how that works.
Pls explain...
#64 is larger than a #69. It's got a bigger hole, allows more fuel.

In order to take a #64 to a #69, IMO, it would be necessary to first solder the jet, before drilling.

Or did I miss something...

Best
rc

 

[biknut]

I'm not clear how that works.
Pls explain...
#64 is larger than a #69. It's got a bigger hole, allows more fuel.

In order to take a #64 to a #69, IMO, it would be necessary to first solder the jet, before drilling.

Or did I miss something...

Best
rc

With machinist drill bits, the smaller the number, the larger diameter the bit. So yes, a #64 is bigger then a #69

 

[porch lizard]

nightcruiser ... this new CNS carb has just the one adjusting screw. The second one closest to the air filter is capped off.

 

[nightcruiser]

nightcruiser ... this new CNS carb has just the one adjusting screw. The second one closest to the air filter is capped off.

Cool, that's the new one I guess... I'd be interested to hear how it works out for ya...

 

[porch lizard]

nightcruiser ... I'm still putting the thing together, making a homemade exp. chamber, and waiting for good weather to try it out. Looking at the forecast for beautiful downtown Scarville, Iowa, that looks to be at least 1 week and possibly 2 weeks. I'll let you know how it runs or doesn't.

 

[JCG]

Cool, that's the new one I guess... I'd be interested to hear how it works out for ya...

I got a new CNS carb with my bike kit. Capped off mixture screw, only one slot on needle for e-clip. Starts good, idles good, ok power on the low end , NO POWER at mid range to full throttle. (bogs down) I can take the cap off the mixture screw. Now what? Where should the float be adjusted?

 

[Greg58]

I wonder why we had to change to the cns carb to meet Epa standards then change the cns so it has only one adjustment screw like the nt. JCG can you post a pic of the adjustment screw side of your carb?