CNS carb working great....

[nightcruiser]

I wanted to start a new thread here on the CNS carb, cause most of the threads are about problems, bogging, broken spacers etc. I have been through a couple week crash coarse on the CNS card and just recently got mine running super sweet, so I figured I a CNS carb success thread was in order....
First some background. I got a new Grubee SkyHawk GT-5 66cc kit this spring, it was a fresh kit dated 04-20-2011 with the newest CNS carb (C-32CNS66-EPA). After assembling I had a hard time getting her running, didnt know what to expect, eventually got her fired up after I realized it was going to take a lot of throttle to make her fire. I couldn't get idle unless I held in the throttle, once I had her rolling I could get a pretty good top end speed but never could get her to idle and slow riding was extremely rough.
I did a LOT of reading of forums etc, tried pulling the vent tube etc, I couldn't find the magic bullet to make this thing run. In the end it took a couple adjustments to get it running right. I waited until I went through the first two gallons of break in gas and moved on to my standard mix (32:1) before I bothered digging into tuning the carb cause I know the mix is going to effect everything.
The first problem with the carb was discovered accidentally. I had hopped on the bike and started riding without turning on the fuel. After running a bit the engine started running great all of the sudden, finally could almost get idle and I was getting better pull on the low end of the throttle. I was really happy, then she died... Failing to start her back up I quickly discovered the fuel valve was off. After turning on the fuel valve she started up but was running crappy again, no idle, dead throttle through most of the range etc. Connecting the dots to the fuel supply I turned off the fuel valve again and sure enough she started running sweet again for a short while then died. This behavior was consistently reproducible, so that got me thinking... Must be fuel level problem, so lets look at the float...
I was reluctant to open the carb on the new kit, I figured its new so it must be right. That's a bad assumption about anything to do with these china girl motor kits! When I finally decided to open up the carb I found it was no biggie. I also found that the screws holding the carb together were loose so I can only imagine it was one giant air leak, you should at very least check those screws before you install your new carb. Also, in the process of working on the carb the fuel inlet nipple fell off, I guess it wasn't pressed down far enough at the factory. Now I know where that little bit of fuel was coming from that would crop up every once in a while!
If you have the carb on the bike you should turn off the fuel and try to burn out as much fuel from the line and carb as possible before you remove it. After you remove the carb unscrew that one screw at the bottom of the bowl that has the red gasket behind it, that is the drain screw, the remaining gas will drain from the carb when the screw is out. Next flip the carb upside down and remove the four screws from the bowl and pull it off. You now have the carb opened up and are looking right at the float.
My next post will be about the float....

 

[nightcruiser]

The float is a rather simple mechanism, 3 parts, float, pin to hold float in place and the needle, no screws or springs to worry about. The operation is also pretty simple, the needle sits inside the valve housing, the float has a tab that pushes up on the needle, when the needle goes up the valve is shut off. BTW, the needle goes into the valve pointed side in. It may seem to work the other way, but trust me, it will leak and you will get gas pouring out of your overflow tube.
First take a moment to familiarize yourself with the float, locate the tab and needle under it, operate the float up and down a few times etc. Turn the carb over the way it sits when on the engine, notice how when float drops the needle comes further out of the valve, examine the travel of the float and needle and imagine it floating on gas in the bowl. Now you should have a handle on what you are dealing with. To get a better handle on it I suggest you (first wipe out remaining gas from carb) connect some new clean fuel line to the carb and blow through it while operating the float. You should feel how it opens and closes when the float operates. Hold the bowl on the carb (with the gasket) and flip the carb upside down while blowing (to simulate the float rising on gas/pushing on needle), you should be able to blow air through when the carb is in normal position and not blow when the carb is upside down. Sometimes crud can get into needle valve and keep it from closing, pull the needle and blow or flush out the valve with some gas, carb cleaner etc. to clean.
To adjust the fuel level in the carb you simply bend the tab on the float that presses on the needle. Small changes are needed, not big ones. I knew my fuel level was too high so I bent the tab so it pushed on the needle valve more, causing it to close the valve when the float was lower in the bowl. If for some reason the fuel level is too low bend the tab so it allows the needle to come out further. There is also another tab on the float on the side, that one limits the lower level of the float. You probably shouldn't need to mess with this, but who knows, you should be aware it is there and why. It's there to keep the float from going low enough to allow the needle to come out so far that it jams when the float tries to push it up.
After I adjusted the float things improved a lot. I could finally get the motor to idle, low end power and smoothness improved, the wet spark plug started looking like it was burning more properly, the gas/oil stopped dripping out of my muffler. Unfortunately the top end went away completely. When the float was too high I had no idle or low end but could hit almost 30MPH if I followed the sweet spot on the throttle, after the float adjustment I got it to idle and low end pull was good but top speed was down to about 15MPH.
I have read people posting about both extremes, some swimming in gas, dripping from muffler, wet plug etc, others not flooding in gas but topping off at about 15MPH, so I wanted to comment about both conditions. After I adjusted the float and had the bike idling well and running smoothly at lower speeds I rode around a bit trying to get my top speed back, or something more than 15MPH. Cruising at WOT (wide open throttle) with her bogging badly I pulled out the "choke" lever (which is actually and extra enrichment jet that adds more fuel rather than restricting air to adjust the air/fuel mix) and the bike surged forward and started to recover some of that top end. This was telling me that she was starved for fuel at the top end, since this extra fuel made such an improvement while running WOT. This gave me the final push that I needed to decide to drill out the main jet a bit to allow a little more fuel to flow at WOT.
My next post will be about what I did with the jets...

 

[nightcruiser]

The main jet is the copper thing there on the inside of the carb, it has a slot cut in it so you can remove it with a (large) screwdriver. The size of the hole in the jet will determine how much fuel can flow during WOT, bigger hole = more fuel flowing.
Adjusting the size of the jet is pretty simple, a couple machinists mini drill bits are used to widen out the hole. These bits are sized by number, #70, #65 etc, the larger the number the smaller the bit. I ordered a small set of drill bits on Ebay that covered sized from #61 to #80 for less than 5 bucks delivered. ( 20 Piece Micro Drill Bit Index Set- 61-80 | eBay ) This set covered the perfect range needed for jetting the CNS carb.
I have read that the stock jet size on the CNS carb should be the size of a #70 drill bit, however, I found that a #72 bit was the largest I could fit into my jet. I do not know for fact #70 should be the stock size, I have just read that in forums a couple times. I have read threads from two other people that drilled out their jets, they were talking about going step by step all the way down the #64 before they hit the optimal size. I decided to start out by opening mine up from #72 to #70 since that was reported to be stock. I had mixed up the #69 and #70 bit in my set by accident so I ended up opening the jet to #69, oops! The other guys said they didnt need to "drill" out the jet, they said the bit could be turned by hand to widen that hole up that tiny bit. I started out that way but was finding it hard to keep a grip on the tiny drill bit and so I clamped it into my drill press and just turned the chuck by hand and it went through the jet really easily. Having the bit in the drill press helped keep it straight up and down and keep the hole nice and accurate. (again, I didnt power the drill press, I just rotated the chuck by hand) In retrospect I think if I had started with a #71 bit, then #70, then #69 I could have done it by hand easily. One step at time isn't much, but three steps was just enough to provide some resistance. I recommend that you only move one size at a time and then check how the engine runs, I was pretty sure #70 was a proper starting point so I jumped right there because I had this carb apart so many times skipping a few times sounded pretty good to me! LOL
If you are worried about screwing up your jet it's not as big a deal as you would think. If you open her up too large you can simply solder it shut and then drill back a smaller hole and you'll be good to go. Or you can buy a CNS carb rebuild kit that includes new jets cheap enough. Or you can buy an NT carb if you have just had it with this CNS carb, I hear a lot of people have done that. I was really close to ordering the NT carb, I would say within HOURS! LOL Fortunately for me I had the drill bits here and figured why not give it a go, if my effort failed an NT carb is cheap enough, but my experiment turned out to be quite a success...
My first ride with the new jet size was pretty awesome! I was happy to see I still had good idle and good low end pull and smoothness, and when I went WOT she roared right up to 30MPH in no time! BINGO! So I had good low end and good top end but she was still bogging mid throttle. Running at mid throttle while bogging I pulled out the choke/enrichment circuit and the bogging stopped, so it seems I am still starved for fuel mid throttle. That means it is time for a needle adjustment, cause the needle is responsible for mid throttle performance...
Next post will be about the needle adjustment...

 

[nightcruiser]

The needle "e" clip is one of the most talked about adjustments on the carb, it controls the fuel flow in the mid throttle range. To adjust the needle you pull the two screws off the top of the carb where the cables go in and the whole unit with slide out of the carb. (this can be done with the carb still mounted on the engine, if clearance isn't enough to get at the screws just loosen the carb a bit and rotate it until you can get the job done) Once out you will see a copper plunger, that's the choke, the black barrel is the slide, the needle is in the slide. The easiest way to remove the barrel is to loosen the tension on the throttle cable as much as possible first, then compress the spring while you slide the cable forward allowing the ball on the end of the cable to come forward out of the slot. It's not that tough, you'll figure it out and get proficient at it soon enough....
Once out you will see there is a little "V" clip inside there, its held in by pressure, just go in there with something small and slide it out, the needle comes out freely now.
With needle in hand you will see the "E" clip on one end, it is probably fitted on the second slot from the top. The needle on my carb had 5 slots and from the factory it was on the second slot from the top. The very first thing I did on my carb was to move the clip down one slot to the middle slot since I thought I needed more fuel.
Perhaps I should go over what is happening with the barrel and needle in the carb briefly so this adjustment makes more sense. The barrel and needle go down in the carb, the barrel blocks off the air flow through the neck of the carb and the needle goes down the fuel jet and restricts the fuel flow, the spring holds the barrel and needle down in the closed position. When you pull the throttle cable the barrel and needle rise up opening the carb for more air flow and more fuel flow.
Since pulling the needle out of the jet is allowing more fuel to flow, moving the "e" clip down the needle (toward the point) is going to raise the needle and allow more fuel to flow, or richen the mix. Since I needed more mid throttle fuel flow and my needle was already on the middle position I moved the "e" clip to the bottom position (closest to the point) and gave that a try.
Couple things about reinstalling the barrel. First you need to put the needle back in the barrel, then put the "V" clip back to hold it in place. Make sure the opening of the "V" aligns with the slot on the barrel. To install the barrel you pull the cable out as far as it will go and put the spring over and compress it, then put the cable ball end through the slot in the barrel and pull back and seat the spring inside the barrel. Not too tough, much easier if you let out slack in the throttle cable first. The barrel and carb plunger just slide back down in their respective holes, there is a long and short slot on the barrel, the long slot goes over the smaller pin inside the carb and the shorter slot goes over the bigger pin at the bottom. (which is the idle screw) You will need to rotate the barrel a bit until it aligns with these pins and it will slide right in. Reinstall the screws and your done!
One quick note on the throttle cable here. Mine was a bit too long, the throttle was loose unless I adjusted all of the tensioners all the way out. I thought that was kinda bogus and have read a couple other people comment about this. I decided to shorten mine to fix that, I simply took some very small single strand wire and wrapped it around the throttle cable a little bit up from the ball end. Then I heated the cable with a torch lighter and soldered it in place trying to leave a ball of solder there as close to the size of the original cable ball end as possible (a higher wattage soldering iron would work for this as well), then trimmed the cable to the new length. This worked out really well for me, however, it did make installing the barrel a bit tougher since there was less slack to be had in the cable.
After I adjusted the needle the mid throttle range came to life, my low end and idle was smooth and strong and my top end hit a record 34.8MPH on my first ride (I weigh a little bit over 200lbs). I have to admit I backed down, was a bit fast for the terrain, she wanted to do more! I call that a huge success, I am completely happy with how the bike is running now and don't feel I am lacking power in any throttle range. So here is a testimonial that it CAN be done, the CNS can be tuned to run sweet!
Keep in mind there are LOTS of variables, different gas, oil, mix ratio, sea level, engine size etc can all effect the way a carb needs to be adjusted. What I have done here worked for me, may not work for you, but I hope you at least get some useful information from what I have written...
I would like to thank everyone who has helped me along the way to figure this all out. I am not a mechanic and knew little about 2-stroke engines and carburetors when I started out a couple months ago, but I have put in the time and research and done the tinkering to achieve excellent results with my bike... Now it's time for riding....
Happy motoring...
Below is a picture of the plug chop after taking a long ride with my current tuning.

 

[decoherence]

great read!

 

[nightcruiser]

Cns carb spacer

About the CNS carb spacer, I had posted this in another thread earlier...

First of all, there is some confusion about the function of this white spacer, the spacer is not the seal, it simply holds the carb in place. The black rubber thing inside the carb at the end of the neck is the seal. When you put the carb on the intake slide it back as parallel with the tube as possible, then when it gets to the end kinda move it around a little while pressing to make sure the intake seats on that black seal the last little bit. I always press the carb firmly onto the intake while I tighten the screw to make sure it gets a tight seal.

I recently purchased two Grubee SkyHawk 2010 66cc kits, one kit had a yellowish plastic carb gasket that was extremely brittle and broke almost immediately. The second kit had a plastic gasket that was more white and you could kinda see through it, that one doesn't seem as brittle and might be ok. Why two kits purchased together and manufactured on the same day have different parts I have no idea... Anyways....

I just got done making a new CNS carb gasket out of a piece of PVC tubing. I used 3/4" white PVC tubing (plastic water pipe), which when compared to the intake will seem a bit too large, at first glance. At second inspection I see the thickness of the material is almost perfect, this got me thinking...

I cut a section to the proper width, filed it flat to exact size, then cut a slice in it (like the original part). I then took a flat file and widened this opening until when squeezed (closing the gap) I could fit it into the CNS carb with a similar gap remaining as the original part. The gap in the new gasket was about 8mm wide when I was done, but reduced when compressed and inserted in the carb. The part looks a little bigger than the original, but when compressed it ends up the same. I tried to fit the carb on the intake, couldn't quite get it on, so I pulled out the gasket and used sandpaper to thin it down on the outside until it fit.

This new gasket is super strong, no way I could crack it with bare hands. And talk about cheap, I found the tubing laying around in the basement, you might have some on your home central air drain tube, at home depot a whole 12ft. stick of tubing is only a couple bucks or less. I used some basic tools for the job, hack saw, vise, flat file, 150 grit sandpaper, that's about it. Only took a couple minutes to make, but take your time, widen the gap slowly and thin down the outer diameter with sandpaper in steps so you don't go to far. Worst case scenario is you have to start over, I guess you could try about 1,000 times with one stick of tubing!


Here is a picture of my home made spacer and a section of the tubing I made it from....

 

[rustycase]

Nice article!
Must get back to working on my carby!
rc

 

[Bill Gaidos]

nightcruiser; sounds like you know more about these engines and carbs than the manufacturer ! hats off to ya' ...and many thanks for taking the time and patience to post all this detailed info for others

 

[nightcruiser]

nightcruiser; sounds like you know more about these engines and carbs than the manufacturer ! hats off to ya' ...and many thanks for taking the time and patience to post all this detailed info for others

Thanks for your compliments Bill. I had written this post a while ago and had expected more response since there were so many posts about problems with the CNS carbs. It's surprising the thread has been so slow, I hope at least some people were able to get some helpful info from it.

I am no mechanic, or expert on these motors (yet), I am still learning about them as I experience this and that. I do, however, have the drive and curiosity to work and figure this stuff out, and a background in engineering doesn't hurt either! Although my major was electrical engineering, mechanical engineering was also a big part of the curriculum. I have always had a great curiosity to know how things work, be it mechanical or electrical, and now with computers. These little motors have given me something to dissect, something mechanical to experiment with that is cheap and FUN.

Did I mention FUN? Riding these bikes is just a gas! Almost every face I see has a smile plastered on it (not quite as big as mine!), except sometimes the faces of parents of young boys who know the next words out of his mouth is gonna be "I WANT ONE!" LOL

 

[Bill Gaidos]

Fun.. I know exactly what you mean. I'm retired, bored , and curious about why and how this affects that, but I've never messed with a 2 cycle engine or carb before, and this has given me something to do that is FUN! Still stumbling through my first build,but loving every aggravating min. Next one should be a cakewalk... thanx to you. Keep on keeping on..

 

[nightcruiser]

After riding my bike all summer some familiar symptoms starting creeping back up. Losing idle so I have to keep tightening the idle screw till its nearly seated, rough low end, stalling when hitting bumps etc. I initially suspected an air leak but never did find one. I cleaned the carb and the problem persisted, fuel delivery was solid, plug looked good, I was confused. So I pulled the carb apart one more time and paid special attention to the idle jet. Pulled it out, cleaned it, tried to ream it with a machinist drill bit but a very tiny #80 was the smallest bit in my kit and it wouldn't fit in the jet. this jet is TINY!
I got resourceful and rounded up some twist ties from garbage bags, striped off the plastic/paper and tried to ream the jet. The bigger/better bags had more sturdy ties and the wire was still too big, the cheap bags with the paper covered ties had a smaller wire that fit right through the jet. I could tell right away after the first time through that something came out of there by the lack of any resistance to this flimsy wire. When done my smallest #80 drill bit still didn't fit btw...
I knew right away when I fired up the bike that the idle jet was causing my problems, cause she fired right up, idle was racing so I had to screw out the idle screw back to where it was before my problems started. A test ride confirmed that she was back to normal, running great through the whole throttle range again with great idle, no stalls, perfect.
This idle jet is really really small, so a very small particle could get hung up and cause a problem here, I recommend that you pay regular attention to this idle jet if you have a CNS carb, and make it your first stop if you run into problems with idle or need to screw in the idle screw all the way to achieve idle. It should be reamed when the carb is cleaned, don't just blow carb cleaner or compressed air down the hole, that did't get get the job done for me.
Just figured I should pass on this experience to other riders with the CNS carb....

 

[PerryP180]

I have run the CNSv2, NT, and DAX RT carbs. on my GT-5. The best one for me is the CNS after a few changes. After a bit of experimenting I wound up with my jet drilled out with a #66 bit(equal to #85 Jet) SBP HD Air filter, and removed the tube from the bowl to the air filter. It is a beast now. I tried adjusting the needle and really couldn't tell any difference. The NT is a stronger hill climber but is significantly slower on top end. The DAX RT had decent top end but terrible hill climbing power. I'm very happy with my CNS setup and have done the same for a few others in Atlanta.

 

[pocdragon]

WHAT A GREAT WRITE UP!

i assembeled my gt5 kit in the spring with a cns carb on it and i never got it to run right

after this extensive writeup ive decided to give it a go and clean and adjust everything

ive searched for a while and this has been the most informational on adjusting and tuning the red cover speed cns carb

 

[nightcruiser]

I have run the CNSv2, NT, and DAX RT carbs. on my GT-5. The best one for me is the CNS after a few changes. After a bit of experimenting I wound up with my jet drilled out with a #66 bit(equal to #85 Jet) SBP HD Air filter, and removed the tube from the bowl to the air filter. It is a beast now. I tried adjusting the needle and really couldn't tell any difference. The NT is a stronger hill climber but is significantly slower on top end. The DAX RT had decent top end but terrible hill climbing power. I'm very happy with my CNS setup and have done the same for a few others in Atlanta.

I recently opened up my main jet from a #69 drill bit to a #65 as an experiment. I found this actually killed my top end. I had to take my spare plastic air cleaner cover and cut some extra slots into it to allow more air to flow, after I did this the top end screems again and she is running good overall with this new jet size.

I also have a rebuild kit for the carb, one day when I have some spare time I am gonna put everything back to stock and see how she runs. I predict miserable failure! LOL Although it might run OK with this rebuild kit, cause I checked the main jet size and a #70 drill bit fit into it, the one that came on my carb would only let a #72 bit through. I have been running on a jet made with a #69 drill bit with standard air filter all summer, nice close to stock tuning...

 

[nightcruiser]

WHAT A GREAT WRITE UP!

i assembeled my gt5 kit in the spring with a cns carb on it and i never got it to run right

after this extensive writeup ive decided to give it a go and clean and adjust everything

ive searched for a while and this has been the most informational on adjusting and tuning the red cover speed cns carb

Yah, I did the same as you, ended up taking bits and pieces of advise from here and there and experimenting until I got mine working right. I can't stress enough how small the pilot jet is and the need to poke through it when cleaning, if this jet isn't perfectly clean your low end and idle is gonna be rough. Float was a big problem too, and the main jet needs to be the size of at least a #70 drill bit. This carb is tricky but once it is tuned it works well.
Post back here if you dig into it and have problems or questions....

 

[nightcruiser]

I have run the CNSv2, NT, and DAX RT carbs. on my GT-5. The best one for me is the CNS after a few changes. After a bit of experimenting I wound up with my jet drilled out with a #66 bit(equal to #85 Jet) SBP HD Air filter, and removed the tube from the bowl to the air filter. It is a beast now. I tried adjusting the needle and really couldn't tell any difference. The NT is a stronger hill climber but is significantly slower on top end. The DAX RT had decent top end but terrible hill climbing power. I'm very happy with my CNS setup and have done the same for a few others in Atlanta.

I wanted to comment about the tube from the bowl to the air filter. I hear everyone say pull this tube out, when I pull the tube out on my bike it runs like crap. It drops the top 10MPH off the ride immediately, put the tube back in and she is rolling again.
A friend has an NT Speed carb, he had commented that he keeps his gas tank topped off because he can tell the difference in how his motor runs when the tank gets low. Since he seems to lose some top end when the tank is low we were speculating that the pressure from a full tank of fuel was facilitating more fuel flow, but when the tank gets low the pressure is reduced and the fuel flow is slowed.
This scenario got me thinking about my CNS carb, particularly that tube from the bowl to the air filter. I could never wrap my head around WHY it was there... Now I am thinking that tube is there to provide some vacume to the bowl, when the motor rev's high the vacume increases, pressure is reduced inside the bowl which makes fuel flow faster from the tank to the bowl.
So it seems to me this tube is there to help keep the fuel flow up with the motor demand when reving high, specially when the fuel level in the tank is low. I can run my tank dead empty and my motor runs the same as when full.
I am wondering if you notice any difference in how your bike runs with a full tank VS empty tank, specially at the top end, with this tube removed? Also, I am wondering if your ride improves with the tube removed simply because it opens up that hole with no filter (no resistance) and lets more air in? Could you plug this hole (on the air filter side) and see if the bike still runs good or if it starts to run like when the tube is connected? Two things come to mind when thinking about the effects of this tube, pulling it could allow more air flow, installing it could cause more fuel flow into the bowl, I am wondering which scenario is responsible for your improvement when pulling the tube? Just curious I guess, cause my bike needs this tube connected.....

 

[nightcruiser]

nightcruiser; sounds like you know more about these engines and carbs than the manufacturer ! hats off to ya' ...and many thanks for taking the time and patience to post all this detailed info for others

The manufacturer has actually asked me for information about what I did to tune my bike... LOL

 

[PerryP180]

I think that they may all be a little different. I believe the tube does create negative pressure in the bowl. That same negative pressure that draws more fuel into the bowl restricts fuel from leaving to the engine. I put a SBP fuel valve on mine and it is a very high flow valve. That would have done away with that fuel restriction. My motor runs the same whether the tank is full or near empty. The SBP HD air filter opened-up the air flow. With all this on the motor will run rough even at idle with the tube hooked up. I actually keep the tube hole taped over to make sure no debris gets in. I don't know why it works, I'm just glad it does.

 

[Bill Gaidos]

CNS carb running good for a while, now plug is black NGK6HS. Is that a lean adjustment on carb., or my needle valve... not reamed out, but down on bottom notch ?

 

[nightcruiser]

CNS carb running good for a while, now plug is black NGK6HS. Is that a lean adjustment on carb., or my needle valve... not reamed out, but down on bottom notch ?

Sounds too rich, what fuel mix are you using? How does the bike run? Easiest adjustment to lean out your mix is to move the e-clip away from the point on the needle. Do you ride most of the time in the mid throttle range? Cause needle adjustment covers mid throttle, the main jet covers WOT.