cns carb v.3 tuning

blazingoutcast · Apr 1, 2012

Ok so far i've dated these new 3rd gen cns carbs back to early febuary 2012 these new cns carbs don't allow u to mess with the air fuel ratio screw and only has one needle seat for the throttle piston

I tried troubleshooting this new carb with someone who has figured out the cns v2 carb i showed him the sealed air/fuel ratio screw and the single seat pin

If anyone has figured out these new gen cns carbs please post on how to get em runnning properly cuz its got a way to rich fuel injection causing the bike to bog and have 0 power when full throttle i had it idling fine and rev fine but when i give it WOT it revs high for a second then bogs out and looses all power if full throttle continued engine will die

Im trading it away for an nt carb n speed carb but would still like to know whats going on with these new carbs for others and for my buddy that's trading me :-||

nightcruiser · Apr 1, 2012

If your CNS carb is running way too rich then you might want to adjust the float a bit. Adjust it so the float closes the needle valve when it is sitting LOWER in the bowl. You can do a simple test before hand to see if you would benefit from a float adjustment. Fire up and warm the motor, then while riding turn off the fuel valve, if the motor starts to run better for a short while before it dies (runs out of fuel), then you would probably benefit from a float adjustment.
I had heard about the sealed air mix screw on the new CNS, didn't seem like that big a deal to me cause I set my air screw and forget about it, I messed with it a bit but didn't see a whole **** of a lot of difference in how my motor runs unless I adjust it to one extreme or another. The single slot needle on the other hand kinda gets me. I definitely did need to make needle adjustments on my carb, I wouldn't want to only have one slot on my needle. I am pretty sure a needle from an older CNS carb would work for you, so you might try ordering a CNS carb rebuild kit and use the 5 slotted needle that comes with it instead. I am not sure if anyone sells just the needle, but the rebuild kit is cheap and having the rest of the parts on hand that come with the kit isn't a bad idea....

rustycase · Apr 1, 2012

It does sound to me like an incorrect main jet.
What does the plug look like, immediately after you give it WOT, and it bogs down and dies?
That will give you the clue what to do...
rc

I dunno abt old/new cns, but an NT needle works fine in a cns V2. Only 4 settings on the needle, though.

camlifter · Apr 1, 2012

yeah, the new cns carb is a pos. ony one notch on the needle and the air adjuster is preset and sealed. it's way to big for a china girl, thats why it needs the plastic spacer to fit the manifold, the new longer off set manifold itsn't much good either, the shorter the manifold the better for these engines.

i don't even try to mess with them. they go up on the back fence rail for rifle practice with the ruger 10-22

rustycase · Apr 1, 2012

Well I'll be!

OK, it just dawned on me...

that needle could be chucked in almost any drill, and a small file could be held against it to cut a few more grooves.

or should I go to 'take a tip, leave a tip' ?

rc

Greg58 · Apr 1, 2012

One thing you can try if the float level is not the problem is more air flow, try a test run without the air filter installed. I have a sbp high flow filter on my cns that helped alot. the red filter is too restrictive I think.

nightcruiser · Apr 1, 2012

Greg58 said:
One thing you can try if the float level is not the problem is more air flow, try a test run without the air filter installed. I have a sbp high flow filter on my cns that helped alot. the red filter is too restrictive I think.

I'm pretty sure the CNS V3 carb comes with a K&N Style high flow air filter, not the red plastic one?

blazingoutcast · Apr 1, 2012

It comes with a blue round cylinder air filter u have to put on a side shifted intake to get it to fit on 90% of bikes

T-lo · Apr 3, 2012

guys, guys! look, it's not really a big deal that the screw is sealed. it's just a cap over the top.
i have a drimmel tool - used the disk/wheel to cut a small line in the middle of the thing and put a flat head screwdriver and turned it off. it's not screwed in, you just need to wiggle it around and pry it off. it was no big deal, and the air adjustment screw is underneath. I thought that would be the case when i first got it and wasn't sure. i was thinking about getting rid of it and thought it couldn't hurt to try.

The needle does have only one place for a clip. but again i used the drimmel very lightly and tried to cut a small grove in the needle and used a crappy pair of wire cutters or needle nosed to even out the indention untill the clip fit. it turned out that i needed it at the top, so i moved it back. i guess i was luckey that i didn't just cut the whole thing into two but i knew that a new needle was like $5. it came out well.

blazingoutcast · Apr 3, 2012

Wait t-lo so the screw under the bowl is the air/fuel ratio screw im confused and did u get ur 3rd gen cns running

T-lo · Apr 3, 2012

no, not a screw under the bowl, but the screw on the left of the idle screw that now has a flat gold cap over the top of it. they say it's "sealed". i was afraid to take it off (expecially because i destroyed it in the process) but you don't need it. under that is the screw for adjustments. This is only for the CNS V3 carb that i know of. I would not have been able to ride my bike if i didn't take it off and make adjustments to air/fuel ratio on account of it running soo rich out of the box i was fouling plugs in minutes.

nightcruiser · Apr 3, 2012

blazingoutcast said:
Wait t-lo so the screw under the bowl is the air/fuel ratio screw im confused and did u get ur 3rd gen cns running

Yes, sounds like the air/mix screw on the CNS V3 has a little cap over it, but you can pry the cap off and the mix screw is underneath. So no biggie, pull the cap and you're good to go. Beyond that the only other limitation is the needle that has only one slot in it, which you can take care of by cutting some grooves in manually, or you can try a needle from a previous version CNS carb or maybe even one from an NT carb. Not SURE these other needles will work properly in the CNS V3 carb, as someone said it seems to be a bit larger, but I am guessing the needle from another carb will work just fine in the new CNS V3. Beyond that, you need to tune the CNS V3 carb just like any other CNS carb out there...

beserkr · May 2, 2012

ok well these grubee engines are pretty much the same so a 66 cc grubee with the cns v3 carb, drill the main jet to #68 mess with the idle mixture screw and check for air leaks? there must be plenty of people on there that know how to tune these?

tooljunkie · May 2, 2012

ok,so my new 48 cc skyhawk is not being very cooperative.
the sealed air screw isnt on the new style carbs,it appears to be eliminated completely.
will have to solder/drill jet to get a better mixture.
needle all the way down,clip at top of needle.fourstroking through midrange.will clear up momentarily but only while accelerating,as soon as i level off,back to fourstroking.

Bikeguy Joe · May 2, 2012

You might want to just run it for awhile. These things break between a two stoke and a four stroke when cruising if they are set up right. It's normal.

That is to say when loaded, they will break into a clean two stroke cycle. At cruise, they break back and forth somewhat. If you want to lean it up a bit, just mix you gas at a lower gas to oil ratio, say 32:1 instead of 40:1. That will make your gas-air ratio leaner.

beserkr · May 2, 2012

I was never able to get a cns v3 to work on a 48cc grubee what's so ever. Adjusting the idle mixture screw and idle speed screw does nothing. I've triple checked for air peaks at the carb to manifold and manifold to jug and found none. I put a short manifold on it with a nt carb and never had another problem. That was just at idle forget about cruising and wot.

Bikeguy Joe · May 2, 2012

Hammer time!

Greg58 · May 2, 2012

It sounds like the powers to be are changing the cns carbs to try to control what adjustments you can make.

tooljunkie · May 2, 2012

i have to go back to my original jet size and start working down from there,i have been running the 2 stroke oil that has sparked some heated debates,i sold it for years and used it just as long in all my two strokes.optimol does work for me,i may go back to castrol and see what the plug reads like.at this point,i know it is an air fuel issue,thinking i shoulda left it alone.the four stroking irritates me.

rustycase · May 2, 2012

TJ, your oil is fine for these engines, IMO. run it at 40:1 and it will be fine after break-in.

IME, Joe is correct, how they will accelerate burning clean, then go into popcorn mode, four stroking at cruise on level ground. It's really not abby normal.

The cns is simply not a good carb for these motors.

A short time ago, Bairdco presented his own personal qualifications, and made some comments on the cns which I feel were very accurate.
Many very experienced fellows have made valiant efforts with the cns.
It's the downright stubborn ones that are still running them! lol

They are quite the challenge!
Good luck
rc

cns carb v.3 tuning

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