having the same carb problem. Leaked gas out the overflow constant. messed with the float tab and after taking the carb apart 6 or 7 times i found a happy spot where i could get it to run and not leak gas. Performance is not good though. Can't give it full throttle and have to mess with the choke alot to eventually go 20 mph or so. Tryed all the needle clip adjustments, tuned the idle and air all different ways, sealed the carb. around the intake with high heat stove sealant, and port matched and polished the air intake and the exhast. what more can i do? I got plenty of gas flow into the carb.took the fuel valve apart and drilled it bigger. Gas tank is venting as well, I can drain my tank with the cap on in about 4 mins. I'm thinking I need to drill the main jet bigger but i also heard maybe the problem is that it is too big already. Sounds like its starving for more gas to me. Help Someone. Theres alot of us out there sruggling with this carb. Something aint right
Help With Carburetor!
- Thread starter locochris
- Start date
the groove you slide the axle into, those are called drop outs. you put a washer on the axle real close to the hub and then put the axle back into the drop outs, this will allow you to shift your sprocket to one side or another roughly 2 millimeters at a time.
the chain is aligned when the chain coming off the drive sprocket (on the motor) makes a straight line to the top of the rear wheel sprocket.
you want to get the alignment as close to perfect as possible, doing it with kit sprockets can be pretty hard and frustrating but it's doable, sprocket adapters can be much easier to set just right but also cost a bit more money.
There is a plus or minus tolerance on this straight shot chain line. Look here this motor is very wide at its sprocket out put. This guy ran the chain close to the wheel. http://motorbicycling.com/f47/death-china-70cc-now-onto-morini-8952-2.html Front derailleurs on multiple crank sprockets don't have a straight chain line.. There is a little forgiveness..
i don't expect him to make a perfectly straight line
but i figure if that's what he's aiming for he'll probably come up short, but at least be in an acceptable range
Perhaps I am mistaken or I have a perspective issue, but the straight line I am suppose to see is not there. Actually, the chain is going outwards and I am not using any spacers but the rubber. How do I actually measure the alignment?
If anyone can share a video on how to tune the CNS V2 carb so the engine can idle I will be very happy.
Thank you for all your help.
I will vouch for the nt carb. My cns carb the idle mixture adjustment screw and the idle speed screw were epoxied in I never could turn them. The speed screw just lifts the slide a little off the bottom most position. The idle mix screw controls the air in the idle circuit. Turning it in richens the mix, the way to adjust the idle mix is to back it out slow till it just smooths out, any more than that is too lean. It won't affect the open throttle bogging problem. I had that cns carb apart 6 times then gave up on it. In my opinion it is junk. It just doesn't draw the air fuel mix correctly and I'm not sure but maybe the problem is the top of the carb you have than richener plunger fandango thing I wonder if that isn't a massive air leak or somehow is screwing up the works. I worked on plenty of two stroke motorcycles when I was younger hondas, yamahas, suzukis, never seen a richener circuit at the top of a carb before. I'm happy with the nt carb I put on last friday the thing runs like a million bucks now idle and all. Better speed and midrange power. I put my cns carb on a fence post and shot it with my 12 guage now I don't have to think I have a spare carb. I don't ever want to see one of those again. Bad idea.There is just one thread after another about the problems with the cns carbs. What problem were they trying to solve? High performance my rump, someone MIGHT be able to help you with this carb, but most of us know and can help you with the NT brand, do you and your engine a favor and get one, I'll give you a link
I noted the vent tube on my cns yd carb was plugged. I drilled through the bottom of the brass vent pipe with a small drill bit and got much better perfomance out of the carb. It must be an error in manufacture that was not caught with quality control. Bill
CNS is a four letter word to a newb like me. It seems you have quite a bit of experience with them. Saint Louis MO 651 above sea level temp ranges from 80-100 ususally humid.
--air leaks sealed
--head is tight
--no leak at manifold or throttle body
--factory setting 2nd notch on needle (not broken in)
--factory setting on air/fuel 3/4 turn from closed
--carb is level
--gas/oil ratio 25:1
symptoms: will not operate at WOT for long without bogging (on flat surfaces no hills here). shuts off when i let the clutch out after slowing. it is dripping from muffler and plug is wet so it is flooding. sounds like the float? dunno please help!! Thanks
--air leaks sealed
--head is tight
--no leak at manifold or throttle body
--factory setting 2nd notch on needle (not broken in)
--factory setting on air/fuel 3/4 turn from closed
--carb is level
--gas/oil ratio 25:1
symptoms: will not operate at WOT for long without bogging (on flat surfaces no hills here). shuts off when i let the clutch out after slowing. it is dripping from muffler and plug is wet so it is flooding. sounds like the float? dunno please help!! Thanks
Sounds to me like you need to check your float. Do you have a inline fuel filter before the carb and tank? I would look into the float more closely.CNS is a four letter word to a newb like me. It seems you have quite a bit of experience with them. Saint Louis MO 651 above sea level temp ranges from 80-100 ususally humid.
--air leaks sealed
--head is tight
--no leak at manifold or throttle body
--factory setting 2nd notch on needle (not broken in)
--factory setting on air/fuel 3/4 turn from closed
--carb is level
--gas/oil ratio 25:1
symptoms: will not operate at WOT for long without bogging (on flat surfaces no hills here). shuts off when i let the clutch out after slowing. it is dripping from muffler and plug is wet so it is flooding. sounds like the float? dunno please help!! Thanks
There could simply be a small crump of dirt sitting at the needle seat/valve at the float keeping it from shutting off. Or perhaps you need to do a float adjustment.
Reading this link should help you get more familiar with these carbs and the general vocabulary. http://motorbicycling.com/f39/motorized-bicycle-carburetor-install-rebuild-302.html
I am also struggling with the CNS carb and have experienced all the stuff you are going through. I still haven't figured it out, but through the various adjustments I have made I have seen these problems go away and others arise.CNS is a four letter word to a newb like me. It seems you have quite a bit of experience with them. Saint Louis MO 651 above sea level temp ranges from 80-100 ususally humid.
--air leaks sealed
--head is tight
--no leak at manifold or throttle body
--factory setting 2nd notch on needle (not broken in)
--factory setting on air/fuel 3/4 turn from closed
--carb is level
--gas/oil ratio 25:1
symptoms: will not operate at WOT for long without bogging (on flat surfaces no hills here). shuts off when i let the clutch out after slowing. it is dripping from muffler and plug is wet so it is flooding. sounds like the float? dunno please help!! Thanks
If you're engine is very wet with gas you most likely have a float problem. With factory setup I couldnt get idle, had to hold the throttle out to keep her running, letting go would always cause a stall, no matter what.... If you are getting fuel out of the overflow tube (that comes from the bottom of the carb) then you definately have a float problem. (fuel level should never get high enough inside the carb to reach the top of the vent/overflow tube). Here's a few pointers on the float, from what I have learned in my experience.
The float is a pretty simple deal, 3 parts, float, pin that holds float in place and the needle (no screws or springs). . There is a tab on the float that pushes up on the needle to seat it and cut off the flow of gas. If there is some crud up in the needle valve it may fail to close off. You can test its operation pretty easily. (after carb is empty of fuel and cleaned) Put some clean fuel line on the carb, hold carb level and blow, if you can blow the needle valve is open. Now turn the carb upside and blow (this makes the float push downward on the needle like it does when it floats on the gas), if you can no longer blow then the needle valve is closed. If it doesnt close you may have some crap in there that needs to be cleaned out. To do this pull the float, drop the needle and connect some clean fuel line to the carb and blow through it (to make sure the needle valve housing is clean). Then put the needle back in (pointed side goes IN, if it is put in the other way it may seem to work but will leak and overflow gas). Then put the float back on and check its operation again to see if it seals off.
As for adjustment of the float, you just bend the tab that pushes the needle one way or the other to raise of lower the fuel level. I have not been able to get an ideal float adjustment yet, if float goes too high the engine swims in gas and wont idle, but has some decent high end. If too low the engine idles nice and has smoother low end power but I get no high end unless I add in the extra fuel from the choke circuit. So adjusting the float seems to send the mix from one extreme to the other, and all other adjustments follow behind the float adjustment.
I am letting my engine cool right now, just about to pull the carb and do another float adjustment. I hope to find a happy medium with the float adjustment so I can get decent idle, low end pull and high end speed, but I am beginning to doubt that is possible with just float, idle and air screw adjustments.
When I had my carb apart last time I put some machinist drill bits down the main jet and found it to accept a #72 drill bit at largest. I have read the stock jet on the CNS should be a #70, and other say they have drilled them out a couple sizes larger with great results. This kinda makes sense to me now. If I adjust the float so the engine has good idle and low end pull I lose the top end, if I drill out the main jet a bit that will give me more gas when I am at the top end of the throttle, which should give me that good top end pull. I have some evidence that this will work out, cause right now the bike has good low end, no top end, but if I open the enrichment circuit I start to get some top end out of it as well.
So, one more float adjustment and if I get no joy then I am gonna drill out the main jet a bit. (and I am also gonna buy an NT carb just so I have one to see how she runs with it...)
I run a 66cns2 carb on my 48cc with a sbp air cleaner and the main jet drilled to a 66, I think a 65 will be right. If yours falls at wot it needs more fuel,till I drilled mine it would bogg at wot. I got 30.5 on flat ground sunday. e-clip on the top notch 40/1 lucas oil at 1000 ft above sea level.
Thanks for your feedback. When I had my float adjusted on the "wet" side I got her up to 29.4MPH, but had poor low end and idle. I just got done with one more float adjustment and while I had the carb opened I rechecked the main jet, #72 drill bit fit. I was going to open her up to #70 but there was a mix up in the bits and she ended up at 69... Just about to go for a test ride and we'll see how it goes... If it improves but doesn't seem quite there yet I will continue to move toward the mid 60's with the main jet....
I would have to call the last adjustment a big success! Ride was really nice, low end pull is solid, high end topped off at a record 31MPH! The mid still bogs a bit so I am about to make some adjustments to the needle.
Right now the idle screw is set out a couple turns, which is a HUGE amount compared to before (when I had to screw the idle screw almost all the way in to get idle).
For the first time I can actually say this thing is running pretty good! I dont know what kind of quality control they have on the carb jets, but I have heard the factory size is #70 (drill bit), but mine was smaller at #72. Opening her up to #69 has brought about a great improvement in everything overall....
Right about now I am really glad I spent the 5 bucks on that machinist drill bit set on Ebay! My set covers from #61 to #80, perfect range for jetting a CNS carb....
Right now the idle screw is set out a couple turns, which is a HUGE amount compared to before (when I had to screw the idle screw almost all the way in to get idle).
For the first time I can actually say this thing is running pretty good! I dont know what kind of quality control they have on the carb jets, but I have heard the factory size is #70 (drill bit), but mine was smaller at #72. Opening her up to #69 has brought about a great improvement in everything overall....
Right about now I am really glad I spent the 5 bucks on that machinist drill bit set on Ebay! My set covers from #61 to #80, perfect range for jetting a CNS carb....
Last edited:
I don't know if you've tried this yet but disconnect the rubber tube running from the bowl to the air filter. When I got my kit it would barely hit 10 mph. Was told to pull that tube and it came to life. Still 4 stroked at wot real bad but that took care of my low to 3/4 throttle problems. Haven't gotten brave enough to drill the jet as I don't know where to get replacements if I screw it up.
I pulled that tube and it did absolutely nothing. I am not disputing your results, but if you look where that tube goes its just under the air filter, I dont know how removing that tube could have such a great effect, but you are not the first to say it has.....
Wahoooo!!!
Just got back from my test ride and all I can say is YES! I finally got this CNS carb running GREAT! The bike idles great, has great pull through the entire throttle range and I hit a top speed record of 34.8MPH! I am sure it will go faster, I had to back off cause I was going so fast it didnt feel very safe! So the bike now goes faster than I want or need to go, and is just running really excellent! I also noticed it is running much smoother and seems quieter as well. She starts up like a dream, barely rolling, pop clutch and bike keeps rolling like nothing happened, pull in clutch and she is just purring like a kitten!
I just can't believe how good she is running now, and am glad I didn't order the NT carb this afternoon out of frustration, almost did, but definately don't need to change carbs the way this thing is running now! I did a plug chop on the way home but havent had a chance to let her cool and pull the plug to check it out.
Let me sum up what got my CNS carb roaring....
First off, check the float. With factory adjustments I had to hold the throttle to maintain an idle. Float was going too high letting in too much fuel. I figured this out when I rode with the fuel off once (by accident), after the fuel level in the carb dropped a bit she started running great. That is what first lead me to the float. After adjusting the float to lower the fuel level in the carb I had good idle and low end power, but no top end.
I fiddled with the float, idle and air screws a bit with no joy, still great low end but the only way I could get top end was to pull out the choke (enrichment circuit). This convinced me that the engine was fuel starved at the top end and I finally got the balls to drill out the main jet a bit.
I bought a machinest drill bit set on ebay for less than 5 bucks delivered (20 Piece Micro Drill Bit Index Set- 61-80 - eBay (item 120761759302 end time Sep-08-11 17:26:04 PDT)) , covered bits from #61 to #80. I found my main jet was at #72 from the factory, have read factory should be #70, but mine wasnt. I ended up drilling her down to #69. It was really simple, didnt need a drill, did it by hand. I started out by hand, but worried I may make a sloppy hole, so I put the #69 bit in my drill press but just turned the chuck by hand. The drill press helped keep the bit streight up and down better than I could have done by hand.
After I adjusted the float and drilled the jet to #69 she idles well and had nice top end, but bogged mid throttle. I had my needle set to the middle notch, since I needed more fuel mid throttle I went two notches down to the last notch (closest to the point of the needle) I know I hear people say the top or second notch is best, but I clearly needed more fuel and you need to pull that needle further out to get more fuel, so bottom notch it is.
Once I did the needle adjustment the mid throttle range came to life and nothing else went to crap (thank god!) So I now have killer performance througout the entire throttle range, great idle, and impressive top end speed. I think my work here is done!!!
She is running so great I don't think I will tamper with it, but I am thinking if I were to drill the main jet out a size or two further I would get better top end performance and could probably move the e-clip on the needle more toward the middle position at that point.
If you're reluctant to drill out the main jet (like I was) I am giving you another real world scenario where that was exactly what need be done to get the CNS running properly. Before I did this I had either good high end or good low end, never both. Now I got it all, she screams! If you are worried about screwing up the jet I would say from the factory it's pretty screwed up, too small to run properly! If you do drill out your jet and have bad results you can either buy a CNS rebuild kit that comes with new jets, or you can solder closed your jet that is drilled too large and then drill back a smaller hole. I really don't think that is gonna happen, as long as you carefully widen the main jet to the size of a #69 drill bit you are going to be thrilled with the results. I have read two other brave souls that have drilled their jets before me, they were talking about going all the way down to #64. I am completely happy with top end speed of 35MPH and the way the bike is running now at #69 so I dont think I will push it any further. The other guys were raving about how their bike was running after they drilled out the main jet, so all you guys out there with CNS carbs that have you frustrated give this a try before you ditch it and get an NT carb. I never had an NT carb, I am kinda new to this, but I think my bike with the CNS carb adjusted like this performs at least as well as it would with an NT carb. There are a couple guys around town that have motorized bikes, I assume they have the NT carb cause they've been at this a while already, I am gonna have to flag one of them down one day and have a little race now that I got her all tuned up!
Good luck to all you CNS carb riders. Let this be a testimonial. It CAN be done! The CNS carb CAN be tuned to provide killer performance.
BTW My engine is a Grubee SkyHawk GT5 66, it has about 180 miles on it and is now running what will be my standard fuel mix of 32:1 using regular 2-stroke oil. I think some of the guys that run the fancy oil at 100:1 ratois may get their bikes to run more like mine simply because less oil in the gas makes more gas pass through the standard (under) sized jet, thus richening the mixture. (just a theory) I don't know why the CNS carb jets come so small, probably something to do with the EPA, but from my experience the main jet needs to be opened up a bit and then she comes to life...
Here is the result of the plug chop after a long ride with the new tuning...
Just got back from my test ride and all I can say is YES! I finally got this CNS carb running GREAT! The bike idles great, has great pull through the entire throttle range and I hit a top speed record of 34.8MPH! I am sure it will go faster, I had to back off cause I was going so fast it didnt feel very safe! So the bike now goes faster than I want or need to go, and is just running really excellent! I also noticed it is running much smoother and seems quieter as well. She starts up like a dream, barely rolling, pop clutch and bike keeps rolling like nothing happened, pull in clutch and she is just purring like a kitten!
I just can't believe how good she is running now, and am glad I didn't order the NT carb this afternoon out of frustration, almost did, but definately don't need to change carbs the way this thing is running now! I did a plug chop on the way home but havent had a chance to let her cool and pull the plug to check it out.
Let me sum up what got my CNS carb roaring....
First off, check the float. With factory adjustments I had to hold the throttle to maintain an idle. Float was going too high letting in too much fuel. I figured this out when I rode with the fuel off once (by accident), after the fuel level in the carb dropped a bit she started running great. That is what first lead me to the float. After adjusting the float to lower the fuel level in the carb I had good idle and low end power, but no top end.
I fiddled with the float, idle and air screws a bit with no joy, still great low end but the only way I could get top end was to pull out the choke (enrichment circuit). This convinced me that the engine was fuel starved at the top end and I finally got the balls to drill out the main jet a bit.
I bought a machinest drill bit set on ebay for less than 5 bucks delivered (20 Piece Micro Drill Bit Index Set- 61-80 - eBay (item 120761759302 end time Sep-08-11 17:26:04 PDT)) , covered bits from #61 to #80. I found my main jet was at #72 from the factory, have read factory should be #70, but mine wasnt. I ended up drilling her down to #69. It was really simple, didnt need a drill, did it by hand. I started out by hand, but worried I may make a sloppy hole, so I put the #69 bit in my drill press but just turned the chuck by hand. The drill press helped keep the bit streight up and down better than I could have done by hand.
After I adjusted the float and drilled the jet to #69 she idles well and had nice top end, but bogged mid throttle. I had my needle set to the middle notch, since I needed more fuel mid throttle I went two notches down to the last notch (closest to the point of the needle) I know I hear people say the top or second notch is best, but I clearly needed more fuel and you need to pull that needle further out to get more fuel, so bottom notch it is.
Once I did the needle adjustment the mid throttle range came to life and nothing else went to crap (thank god!) So I now have killer performance througout the entire throttle range, great idle, and impressive top end speed. I think my work here is done!!!
She is running so great I don't think I will tamper with it, but I am thinking if I were to drill the main jet out a size or two further I would get better top end performance and could probably move the e-clip on the needle more toward the middle position at that point.
If you're reluctant to drill out the main jet (like I was) I am giving you another real world scenario where that was exactly what need be done to get the CNS running properly. Before I did this I had either good high end or good low end, never both. Now I got it all, she screams! If you are worried about screwing up the jet I would say from the factory it's pretty screwed up, too small to run properly! If you do drill out your jet and have bad results you can either buy a CNS rebuild kit that comes with new jets, or you can solder closed your jet that is drilled too large and then drill back a smaller hole. I really don't think that is gonna happen, as long as you carefully widen the main jet to the size of a #69 drill bit you are going to be thrilled with the results. I have read two other brave souls that have drilled their jets before me, they were talking about going all the way down to #64. I am completely happy with top end speed of 35MPH and the way the bike is running now at #69 so I dont think I will push it any further. The other guys were raving about how their bike was running after they drilled out the main jet, so all you guys out there with CNS carbs that have you frustrated give this a try before you ditch it and get an NT carb. I never had an NT carb, I am kinda new to this, but I think my bike with the CNS carb adjusted like this performs at least as well as it would with an NT carb. There are a couple guys around town that have motorized bikes, I assume they have the NT carb cause they've been at this a while already, I am gonna have to flag one of them down one day and have a little race now that I got her all tuned up!
Good luck to all you CNS carb riders. Let this be a testimonial. It CAN be done! The CNS carb CAN be tuned to provide killer performance.
BTW My engine is a Grubee SkyHawk GT5 66, it has about 180 miles on it and is now running what will be my standard fuel mix of 32:1 using regular 2-stroke oil. I think some of the guys that run the fancy oil at 100:1 ratois may get their bikes to run more like mine simply because less oil in the gas makes more gas pass through the standard (under) sized jet, thus richening the mixture. (just a theory) I don't know why the CNS carb jets come so small, probably something to do with the EPA, but from my experience the main jet needs to be opened up a bit and then she comes to life...
Here is the result of the plug chop after a long ride with the new tuning...
Attachments
Last edited:
Greg here, I don't know which engine Perry is running but on all the 48cc grubee's we have built removing the vent tube made a world of differance. It turned out that at about 3/8 to 1/2 open the vacume from the engine was drawing fuel up the vent tube into the carb through the air cleaner, some say it did not help them but on all six 48cc we built this was the trick.
So, by simply pulling out this vent tube you were able to get a CNS carb to run on your 48cc with good response through the entire throttle range?
I ran a while with the vent disconnected, didnt see any change what so ever so I put it back. Maybe my 66cc needs more fuel than your 48cc? Then again, if my jet was really at #70 from the factory as others have reported, I guess I would have been happy with it from the get go, cause it was opening the main jet from my stock #72 to #69 that got my bike running sweet. Maybe they just put a bum jet in my carb, I donno...
I got one more identical kit that I will be building up as soon as the dude finds a suitable bike, so I will see then if I have the same problems with the carb and find out what size that jet is. I know I have read about nothing but problems with these CNS carbs, haven't really heard anyone say they are happy with their performance except us few that have drilled the main jet. Are you happy with the performance you are getting from the half dozen you have built after just pulling this vent tube and adjusting the idle and air screws? (assuming CNS carb?)
All six engine kits came with the 66cns2 carb, the main jet is the same size on both kits. This may be why a 48cc with stock air filter and the vent tube removed runs fairly well. I have read on this forum of a 48cns2 but have not seen one. The differance between my bike and the others is with smoother air flow and larger main jet is much better mid range and hill climbing. By the way I had to open up the pilot jet or some call it the idle jet,mine would let fuel pass through but you could not see the sun through it. I used my torch tip cleaning file set to run through it to clean it up. I can start my engine by lifting the rear wheel and spinning it by hand one or two times even if it sets for a few days.
I will have to pay some more attention to the pilot jet next time I have the carb open. First time I opened it I did take a tiny wire and poke through all the jets and made sure I can see through them etc.
I just got done with a ride, climbing a steep hill from dead stop my speed was in the teens in just a bit over average time for flat land, and kept increasing speed as I climbed the hill, when I hit the top I was doing 25MPH. I was really happy with that performance, the people in the cars around me were surely shocked! LOL It's fun to watch people react to the bike, except the ones that gape so bad they get in your way and wont let you ride!
Just out of curiosity sake, do you have any idea what the size is on your main jet? I got a feeling mine was unusually small at #72...
