OMG I have to tune a CNS!!! Help

I was talking to a guy I get some of my parts from, he has a whole garage full of these engines and is really into them.
I asked about my carb and he said they come way to rich. This is exactly what I had thought by the performance I got from it. Yet everyone here says you have to drill the jets larger.
The guy said these carbs should be used with an expansion chamber pipe too

I think those drill bits are coming today but now if I need to go smaller they are useless. Luckily I found a case of bits here and I think they may go smaller too

But now im debating weather or not to even attempt to tune that carb, since it will most likely take alot of time
plus how much work it takes to get the throttle changed out
 
well also if you read alot of the threads alot of drilling was done because no jets were available, and on the real cns carb. jets are available now
mine isnt a real one its whatever BGF sells, maybe its not leaned out like alot of ones came because of epa bs


now im no carb expert, but im really good at tuning rc engines
and I have tuned a few scooter carbs, dirt bike carbs and know when it feels lean or rich

mine felt rich, plus a loss of 4 mph over stock is a good sign of that
 
SdCruizer said:
well also if you read alot of the threads alot of drilling was done because no jets were available, and on the real cns carb. jets are available now
mine isnt a real one its whatever BGF sells, maybe its not leaned out like alot of ones came because of epa bs


now im no carb expert, but im really good at tuning rc engines
and I have tuned a few scooter carbs, dirt bike carbs and know when it feels lean or rich

mine felt rich, plus a loss of 4 mph over stock is a good sign of that
Click to expand...

What's your spark plug look like?
 
never checked on the new carb, I only messed around with it a short time
put the stock back on, since I had read so much about having to drill it out I figured I would have to wait until I get the drill bits

acceleration from a stop was very smooth, but top speed seemed way to rich
also it would rev really high on idle, then take forever to climb down to a low idle

I read about intake air leaks maybe I had that, mabe it was the air screw
I could only keep it like 1/2 turn out any more and it would die

so if I ever try it again I will try to seal the intake, even though I did have white grease on it to help slide it on maybe I had a leak, not sure



now my plug now with the stock carb upjetted for the air filter looks fine
 
I have heard it said that with 48cc motors people need to lean up their carbs, I know for a fact that with my 66cc motor running a CNS carb was way too lean. I had to drill out my jet a bit and then she came to life....
Asking around I found the consensus is that the stock CNS main jet opening should be the size of a #70 drill bit, mine was smaller, I could only fit my #72 drill bit through it. Before I drilled it out she ran good up until around 75% throttle, above that she bogged bad. I was able to determine the condition above 75% throttle was lean by riding the bike into the throttle range where it bogged, while bogging I opened the "choke" enrichment jet and the bogging went away. Since the extra fuel from the enrichment jet fixed the bogging I knew it needed more fuel, so I drilled.
I first drilled from the original #72 opening size down to a #69 (by mistake, I was aiming for #70 but mixed up the drill bits) When I put the carb back on the bike the bogging was gone above 75% throttle and she ran great over all. I am very happy with my CNS carb now. Since then I have opened her up to #66 drill size with not much improvement, I needed to increase the air flow at this point I think to see any more improvement but winter was setting in and I didn't get a chance.
A couple of observations about the CNS carb...
First of all, lots of people think the white spacer/bushing is the seal, it is not. The seal is that black rubber grommet that is inside the carb neck, the white spacer just holds the carb in place. You MUST seat the intake on the BLACK GROMMET properly or you will get air leaks. I push the carb down the intake until it bottoms out, then kinda wiggle it a bit and push it on that last little bit so it seats into the black grommet and then tighten it down. I have never had to use any sealer on my carb to prevent air leaks when I install the carb in this manner.
Secondly, the "choke" on this carb is an extra enrichment fuel jet, not an air restricting choke. This jet is extremely small and clogs easily, if this jet clogs you will have poor idle and low throttle range performance. My bike rode rough at low speeds until I reamed out the crap from the enrichment jet, after that my low end smoothed out nicely.
Finally, I find the float on the CNS carb has a strong influence on how it functions. You may need to adjust the float setting a bit to get your carb performance where you need it, specially if your carb is not mounted level.
This all may seem like a lot of work, but the carb is really simple and not hard to work on at all. When you remove it from the bike take the two screws off the top and the cables pull right out, now the carb comes off easily without being attached to any cables. There are 4 screws that hold the bowl on, inside there aren't many parts, the only parts that come out are the float, its pivot pin and the needle that is underneath it. Thats it. I fiddled with the float adjustment a couple times before I got it right, and took a very thin wire and pushed it through the enrichment jet to clean it, which I do every time I open her up now. The hole is so tiny I had a hard time getting something that would fit through it, I ended up stripping the paper of a wire from a garbage bag tie and used that bare wire. The first garbage bag tie I tried was from a quality bag, the tie was plastic covered and the wire was too large to fit (believe it or not). The next one was from a generic garbage bag and it was a paper covered wire which was thinner and fit through the enrichment jet perfectly. I will state it again, cleaning out this enrichment jet is very important for good idle and low end smoothness on the CNS carb.
If I read the message properly, you purchased a CNS carb as an upgrade and quickly gave up on it and went back to the NT or Speed carb. Most people seem to be doing the opposite, they have a CNS and buy an NT or Speed to replace it. At any rate, I would like to encourage you to work with the CNS carb a bit when you have time, keeping in mind what I have written above. A little playing with the float and getting those jets properly sized and cleaned should get her running well, I think properly tuned you might be more satisfied with the performance of the CNS carb than your stock carb....
 
N/c it depends on each engine what size the jet should be, mine is on a48cc with a sbp filter and I'm at a 64. I dont recomend this size but thats what mine likes, it by far faster than the bike with the nt.
 
Greg58 said:
N/c it depends on each engine what size the jet should be, mine is on a48cc with a sbp filter and I'm at a 64. I dont recomend this size but thats what mine likes, it by far faster than the bike with the nt.
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Just to clear Greg, you're talking about a # 64 drill bit, not a size 64 jet?
 
I agree, the jet needs to be tuned to the motor. Depending on the flow of the air filter and exhaust on your system etc, you may need a bigger or smaller jet.
I would say the best thing to do is get the air filter and muffler all set the way you want it first. Evaluate how she runs with those parts in place, particularly the condition when running WOT. Depending on the WOT condition, open up the main jet step by step with a set if miniature drill bits until she is running properly at WOT, then adjust the "e" clip on the needle to set conditions right for the mid throttle range. If she happens to be rich at WOT you can either buy a smaller jet or solder the jet closed and drill back a smaller hole in it.
I bought a set of drill bits on Ebay for $5 bucks that covered sizes from #61 down to #80, perfect range for jetting these carbs. You might want to have a micrometer too, caues the drill bits are almost impossible to tell apart otherwise if you get them mixed up....
As someone stated, the CNS jets are now available for purchase, and a CNS carb rebuild kit is cheap and comes with a complete set of jets for the carb, so if you screw up its not a big deal....
 
I finally got my cns clone carb tuned
I had to down jet it. Ended up using drill #70, also equals a #70 jet too
I found stock to be a #72 jet. I knew it was too large the way it ran last week when I tried it, even though it seemed everyone says to up jet them.
I did try a #72 drill bit too and got same top speed, but I figured might as well go a touch richer. Had to adjust the needle jet to get rid of slight bog.

One thing I can say, its really helped acceleration. I use a cen clutch and stock carb it would make it chatter accelerating from a stop. Now this new carb the clutch is silent and engages stronger. Nothing to blow you away but little things like that is nice.
I want to run it harder before I check the plug but im sure its set good, if anything little rich.

So from alot of pics seems all the extra nipples just vent to the air so I put short pieces of hoses on them. Only one spits up fuel I think its the float vent cant remember.

Throttle also feels different must be the spring, maybe its softer but feels good. I hate the remote choke lever
tested in about 60F temps
tomorrow should be warmer so im curious to see how it does

also the carb is very quiet compared to the stock with a large filter

I have the same stretch of road I gps my top speed on in front of the house, I gained 2 mph over the stock carb
 
Got a question
still messing with my carb, I finally counted the idle air screw turns and im only 1/2 turn from tight

any more and it bogs like crazy at idle then dies
now to me this means the pilot jet is too rich correct
since my main was way to rich, it only makes sense

messed with it again tonight, changed the main again
now so far I have it at a #72 drill bit and needle up one notch from center (leaner)
tried richer and all the way lean with the needle

I have a pack of numbered bits in the range of 61-80

I noticed when its cold it takes a long time to warm up, like 4 min until it will hold idle

should I mess with the pilot jet? any idea what size it is near so I can see if I have any drill bits

or leave it as it is, I think its doing pretty good

once warn it does idle just fine

so far plug is dry, but blackish on the porcelain
means rich but tomorrow I will be riding it hard and will check then
ive only been going around the block when jetting it
 
SdCruizer said:
Got a question
still messing with my carb, I finally counted the idle air screw turns and im only 1/2 turn from tight

any more and it bogs like crazy at idle then dies
now to me this means the pilot jet is too rich correct
since my main was way to rich, it only makes sense

messed with it again tonight, changed the main again
now so far I have it at a #72 drill bit and needle up one notch from center (leaner)
tried richer and all the way lean with the needle

I have a pack of numbered bits in the range of 61-80

I noticed when its cold it takes a long time to warm up, like 4 min until it will hold idle

should I mess with the pilot jet? any idea what size it is near so I can see if I have any drill bits

or leave it as it is, I think its doing pretty good

once warn it does idle just fine

so far plug is dry, but blackish on the porcelain
means rich but tomorrow I will be riding it hard and will check then
ive only been going around the block when jetting it
Click to expand...

The air screw only adjusts the idle. If it idles good, that's all you get from it. Most of the CNS have good idle. That's all most people to start out with. Mine idled great out of the box, but as soon as you gave it the gas it fell on it's face. It only did about 10 mph. Most people report something like that.

I had to drill the main jet larger to get it to run at higher speeds. You can tell by turning on the enrichner. If that makes it run better it's too lean. I'm talking about when it's warmed up. I drilled the main to a #64 drill bit.
 
my carb has 2 screws, but it was bought from bgf so im sure its not a real cns but looks like them

my idle is great warmed up, but when cold takes 3-4 min of me revving it to keep it alive. I think I will just twist the idle screw 1/2 turn when cold then when warm twist back to lower idle

I have tried the enricher when riding, it bogs and tries to die with barely any
tells me im flooding it


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my carb you had to push on very tight for it to fit on the intake tube, also put a little sealant just to ensure a good seal but that was just done yesterday. It seemed to seal fine during all the tuning

but when I originally installed and tried to tune it idle was all over the place
I must of had an intake leak and I wonder if I didnt how it would of worked then
 
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
 
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...
 
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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
 
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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.....
 
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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