OMG I have to tune a CNS!!! Help

SdCruizer said:
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
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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.
 
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
 
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 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.
 
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.
 
porch lizard said:
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.
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No needle slots, really? That sucks, I would order a rebuild kit and put an adjustable needle in there right away....
 
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.
 
porch lizard said:
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.
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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....
 
Greg58 said:
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.
Click to expand...

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
 
rustycase said:
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
Click to expand...

With machinist drill bits, the smaller the number, the larger diameter the bit. So yes, a #64 is bigger then a #69
 
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.
 
nightcruiser said:
Cool, that's the new one I guess... I'd be interested to hear how it works out for ya...
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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?
 
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?
 
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Not easily. The carb has YD cast into it. Idle adj. screw and mixture adj. screw (closest to air filter and capped off) and the letters C-32CNS66EPA on the fuel bowl. (I think the first letter is C...It's kinda smeared)
 
JCG said:
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?
Click to expand...

You should warm up the motor and then do a plug chop while riding in the region that you are experiencing bogg. Then let the motor cool down and pull the plug and examine it to try and determine what condition is causing the bogg...

Here is a very handy guide to help you read the spark plug and determine the condition. After you decide if it is running lean or rich then we will know how to adjust....

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Also, an easier test you can do with the CNS to determine if its running lean or rich... Warm up bike, ride into the range where the bogging occurs, while bogging pull on the Enrichment Jet (choke lever), if the bogging goes away or is reduced then the bogging was caused by a lean condition (since the Enrichment jet added extra fuel and richened the mix), if the bogging continues or worsens with the choke lever pulled then you are too rich already....
 
they cap off the mixture screw because EPA regulations mandate it, to keep people from adjusting them richer and spewing unburnt hydrocarbons into the air.
 
JCG said:
How do you adjust the mixture with the screw capped off and only one notch on the needle?
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I would look into determining what adjustment in the mixture need be made before worrying about how it can be done. The cap on the air mix screw can be popped off and the screw is there below, but the air mixture screw adjustment isn't going to cure a situation where it runs good at low RPM and boggs at mid to full throttle...
 
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