CNS Performance Carb on 49cc Kit

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4n6days

New Member
May 17, 2012
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West Chester, PA
I recently bought a used motorized bike.

The previous owner said it was a 49cc, although I don't see the displacement stamped on the cylinder anywhere.

It has a CNS Performance Carb like this one:



I have a few problems.
1.) The carb doesn't fit tight on the intake manifold
2.) It seems to be running RIDICULOUSLY rich.

I moved the clip on the throttle slide needle to the top groove and the mix screw is all the way in. When it runs, any throttle immediately kills it, and is accompanied by gobs of smoke out of the muffler and even fuel dripping from the muffler. Even left to idle it eventually gets very smoky and dies. When this happens and I take the plug out, it's wet.


Any ideas on how to fix the carb fit and the mixture problem?

Anyone have a stock carb they want to trade for a CNS?


(One more thing) The bike originally had an AutoBike 5 speed automatic shift system, but the derailleur is pretty much trashed (bent beyond repiar). I was just going to shorten the chain and add a masterlink and make it a 1-speed. Does that sound like a resonable (cheap) solution.
 
Al.Fisherman

Al.Fisherman

New Member
Sep 9, 2009
1,966
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Calera, Alabama
Once you mentioned you have a CNS carburetor (in your title post), I read enough. Sell or trash it, and buy a NT or a NT speed carburetor. That all I have to say about that.

Unless the drive gear cover has a placard, it's hard to tell weather it is a 49cc or a 66cc, unless you measure the cylinder diameter. One other way is if it has 6mm cylinder head studs, it would be a good bet it's a 49cc.
 
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4

4n6days

New Member
May 17, 2012
3
0
0
West Chester, PA
$15 isn't too bad. I kinda bought this bike as a trial run. I want to build one from a kit, but I wanted to get an idea of what they were like before I bought a new one. (In hindsight, I should have just spent the money on a kit). I picked this one up for $140 for the bike and all. hopefully I can get it rideable and sell it for what I have in it. We'll see.
 
Y

young grease monkey

New Member
Sep 20, 2011
362
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Chicago
Maybe the choke is on? See if the cable is too tight before you junk it. And the mix screw should be turned out to make it run leaner, not in. That is part of the problem. Also pull off the bottom of the carb to see if the jet screw is loose. It's the brass screw with a hole in it. I have a cns and it works just fine. Maybe I got lucky. But it definitely shouldn't run super rich. Cns carbs are better suited to the 66 CC because they are bigger than the NT, so I would get a different carb anyway. I don't like the quality of NT carbs, they are kinda cheesy. But if you are going to sell it anyway, try to fix the cns and if you can't, get an NT.
 
Hoze513

Hoze513

New Member
Nov 24, 2011
262
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42
Joliet, illinois
I have a 66 pk80 engine with the CNS. And it was running rich too, the same thing I had to have the mixture screw all the way in for it to run. Until I got a SBP muffler. Now it runs a lot better. Just needs to be jetted.
 
Greg58

Greg58

Well-Known Member
May 1, 2011
5,353
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Newnan,Georgia
As was stated in post 6 the mixture screw should be turned out to lean in to richen. This is for the idle, the screw goes into a small passage to block or increase the amount of air that flows into the carb with the barrel close. Once you open the throttle the needle clip location controls the mixture.
 
N

nightcruiser

New Member
Mar 25, 2011
1,180
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USA
You need to adjust your float so there is less fuel in the bowl, that should fix up your rich condition and fuel dripping right quick. Also make sure the needle valve is clean.
My CNS runs GREAT, if you don't mind doing some very simple adjustments to your carb yours will too. Don't listen to all the folks that tell you to toss the CNS in the trash etc, IMHO they are just lazy or lacking the skill to tune their carb. If you want to go the easiest route then go ahead and try an NT carb, they are definitely easier to tune because they only have one jet compared to the CNS's 3 jets. Tuning a CNS carb isn't impossible or nearly as difficult as many would lead you to believe, and when they are tuned up the run really well...
I really wish people would stop passing out advice like "throw your CNS in the trash" when people ask for help. If you don't want to help them then perhaps it would be more appropriate to say "the CNS is more difficult to tune than the NT carb, so if you don't want to mess around tuning your CNS carb try an NT". The truth is CNS carbs can be tuned, do run great, and its not that difficult if you put in the effort. You might even learn something in the process...
 
Greg58

Greg58

Well-Known Member
May 1, 2011
5,353
2,575
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Newnan,Georgia
Hey nightcruiser you and I are amoung the few that like the cns, I have been trying to get my other bike with the nt to run as good as my cns but haven't got there yet. The potential for better performance is in the cns because of the larger barrel and the ability to flow more air.
 
N

nightcruiser

New Member
Mar 25, 2011
1,180
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USA
I think there are more people running the CNS carb than you would tend to believe, but there are a few here in the forum that are extremely vocal with their "CNS is crap, throw it in the trash" lines, which kinda makes tuning one look like "mission impossible". It's not.
I wrote a thread about tuning my cns, it is located here: http://motorbicycling.com/showthread.php?t=32736&highlight=cns+carb+working+great
In that thread you should find lots of info that is helpful in tuning your carb, including how to make a spacer for next to nothing that will definitely hold your carb on your intake tigtly....
 
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