OMG I have to tune a CNS!!! Help

biknut

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Sep 28, 2010
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I'm thinking after all this, the thing is still a little on the lean side. It's running 24:1 mix for break-in which is probably leaning it out a tiny bit too.

I'm trying not to drill the jet out so far that it'll be too rich on the regular pre mix after break in.
 

biknut

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Sep 28, 2010
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The thing about this carb is it performs different on a 48cc, all six of the bike we have built here in Ga. had to have the vent tube removed to run right and to get a good plug reading. The e-clip setting on all are on the 2nd or 3rd groove, this works well at 1000 ft a.s.l.
I have no idea about tuning a 48cc with this carb. My only experience with this carb is limited to this one motor so far. A Grubee SkyHawk 80.
 

Greg58

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May 1, 2011
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I understand from what I have read on other threads the C-32CNS66-EPA carb is for a 66cc kit, but thats the carb we got with ours. This may be why the main jet works ok for 48cc .
 

biknut

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Sep 28, 2010
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Drill that sucker out and if it ends up too rich, use some solder to fill it back in and redrill for the next size smaller
That's probably good advise. I've never soldered up a jet before, but on the other hand I can't remember ever drilling one before either.
 

biknut

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Tonight Corinne came over and tested her bike, that I'm tuning this CNS for. I guess I'm doing pretty good so far. She waxed my ass on my bike, the Atomic BB. I guess now I'll have to stop saying the Atomic BB is the fastest MB in Farmers Branch. I'm #2, I'm #2.
 

Greg58

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May 1, 2011
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It seem like the cns carb does boost performance if you can figure it out, I don't have a bike with a nt to compare mine to. Mine is a 48cc and I get 32 on flat ground and have reached 35 down hill, I won't do that again!
 

merchant810

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Jun 13, 2011
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Thank you so much biknut. Im on my first build and its an occ schwinn chopper. Everyone said the motor mounts and clearance would be the tough part until i received this carb. I was ready to give up but after reading your thread have a whole new perspective on my project. Please continue posting any new findings with your experiment and i look forward to going at it again tomorrow with my newfound information.
 

biknut

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Sep 28, 2010
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Thank you so much biknut. Im on my first build and its an occ schwinn chopper. Everyone said the motor mounts and clearance would be the tough part until i received this carb. I was ready to give up but after reading your thread have a whole new perspective on my project. Please continue posting any new findings with your experiment and i look forward to going at it again tomorrow with my newfound information.
Thank you, and good luck. If you can find the drill bits you need I'm sure you can get it to run better. Please let me know how it turns out.
 

merchant810

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Jun 13, 2011
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Ok so i got ahold of a 65 and a 64 bit, so i will start with the 65. What notch is your c clip on the pin on, all the way at top? also for now i just have the stock air filter do you suggest putting kn oil on that? and im not sure if i need a new spark plug mine came with one with three prongs, is that the ngk? thanks for all your help im very excited to test this out.
 

Greg58

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May 1, 2011
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If you drill the jet out you can start at the top groove with the e-clip and do plug checks as you move the clip down till you get a light brown plug.
 

merchant810

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Jun 13, 2011
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okay i just drilled it out and am putting it back together. sorry for all the small random questions but my manual says for break in period use 18 to 1 ratio is that recommended by you guys cause at this point i burned the manual and am going straight from the pros. I also uploaded pics of my build if you want to check them out.
 

merchant810

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ok so i drilled it to the 65 bit and wow, it made a huge difference. I can actually use the throttle and get a response from it. Its insane how much different it is it actually controls the motor through accelerating so much better. It was late when i tested it and it idles pretty high so i may adjust that. Couple of questions.
1. It now makes a popping sound when running, is that good or bad.
2. When i get to a certain speed/rpm it acts like there is a rev limiter and the motor revs out of control like its freespinning and actually pulls on the bike. when i pull the clutch, slow down a bit and let go of clutch it is still in the extremely high rpm. I dont believe my clutch is slipping im almost positive.
3. For the spark plug test do i go to full acceleration till it revs out of control then hit the kill switch to check it.
4. The choke has to be all the way pulled down for it to run at all. The second i try to pull it up an inch it dies. On my dirtbike if i tried running it with the choke wrong it would rev without pulling at a certain point is this what im dealing with.
Thanks for the fuel advice i thought it might be heavy and thanks for all the help. I can tell you guys know whats up and ill have this bike running soon.
 

biknut

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Sep 28, 2010
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A #56 is pretty big. As long as it's running good it won't hurt to run a little rich.

I like to set the main jet first. This is how I check the plug. Run it at full throttle as long as possible. At full speed quickly chop the throttle, and simultaneously pull the clutch lever in, and hit the kill button. Then I peddle for a while to let the motor cool off a little before checking the plug. If your plug is black, you're running too rich. You can solder the jet up and redrill it.
 

Greg58

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May 1, 2011
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The choke is off when the cable is all the way in, sounds like you have the jet sized ok next adjust the idle. The idle adjusts with the two screws. then the e-clip for mid. range. I know it takes a little time but it will be fun to ride after you get it right!

Hey Biknut I did have to drill out the idle jet on my carb. it was allmost closed from the factory. I didn't have the drillls at home so I used the smallest torch tip cleaner from a folding set like a allen pack.
 
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merchant810

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Jun 13, 2011
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lol sorry biknut i meant to say i drilled it to 65. so it has the throttle response but doesn't go as fast as i feel it should i feel it tops out before getting full pulling power. This could be because the motor is still only been ridden for bout a half hour lol. I might just be impatient, anyway i checked the spark plug and the top threads were gooey black but the three prongs were a charcoal dry black. I ordered the ngk and will pick it up tomorrow so i can check a clean plug and know where im at. Is it just the break in why it reaches max rpm but doesnt go very fast.
 

GearNut

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Aug 19, 2009
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Don't read a spark plug by looking at the color of the threads. Look at the color of the porcelain insulator in the very center of the spark plug, the part that holds the center electrode in place.
This link has good pictures of proper coloring for a 2 stroke engine's spark plug.
If you read the text though, you may get confused a bit as it is from a small aircraft website.
Principles of 2-Stroke Jetting & Reading Spark Plugs
 

biknut

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Sep 28, 2010
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lol sorry biknut i meant to say i drilled it to 65. so it has the throttle response but doesn't go as fast as i feel it should i feel it tops out before getting full pulling power. This could be because the motor is still only been ridden for bout a half hour lol. I might just be impatient, anyway i checked the spark plug and the top threads were gooey black but the three prongs were a charcoal dry black. I ordered the ngk and will pick it up tomorrow so i can check a clean plug and know where im at. Is it just the break in why it reaches max rpm but doesnt go very fast.
I think you'll find a really big difference just from the plug. IMO the stock 3 prong plug is a poc. Even if we call it a good plug, it's the wrong one.

How fast are you getting up too now?