66cc Tuning a YuanDung Skyhawk C-32CNS66-EPA Carburator

[KoolBreeze420]

I'm trying to tune this carburettor and it's not easy. It has 2 jets 1 for idling and another I guess for throttling.It has an Idle screw and an Air screw. I can ride it but when I stop and allow it to idle it has a lot of exhaust and getting it to a mild idle is hard and when I did get it I wasn't able to throttle, it would bog and stall. Currently, if I try and open the choke it stalls if I throttle it stalls if I stop it's a bit too high and too much exhaust and sounds too fast the problem is having 2 screws to contend with and no information on how to try tuning it. Please, any tips on how to tune this thing would be great. This carb has so much power it will transform my bike and allow me to actually pull my trailer with a load up a hill without me having to pedal like a maniac.
http://www.motorizedbicycle.ca/aftermarket-parts/adjustable-cns-high-performance-carburetor-kit.html

 

[Street Ryderz]

Yes that carb has two jets the pilot(idle)jet and the main (wot)jet both have to be set up properly to get the best performance out of it!But there is the needle between the two witch also has to be set up but first you need to set the idle and transition from pilot to neddle so you can see if the pilot jet is even the right size,And this is where the air screw comes into play as it's turned in it richens the idle circuit out leans it you will want to start at 1 and a 1/2 turns out from closed and start the engine let it warm up and if the idle is high turn the air screw in 1/4 turn and wait 30 seconds or so to let the change take affect if still to high turn the idle set screw out and repeat until the desired idle speed is set!Then twist the throttle a little 1/8th of it's rotation does the engine respond quickly and clean or does it hesitate and sound rough if cleanly might be good or a bit lean for witch you can raise the needle one notch and will be good,If slow and rough the needle gets dropped a notch by raising the clip!Once thats setup you can now ride the bike to check the transition between needle and main jet and the main jet as you throttle up from 3/4 to wot the transition and full throttle position should also sound clean and pull some more until the top rpm is achived if it does this quickly and seems flat it's lean to slow and strugles to get rpm is to rich! It's a great carb very tunable once you know how to do it and has great potentail for performance!The only thing that is wrong with it is the stock air filter body (stock red one) is very restrictive when I removed mine I had to go up 10 jet sizes to match the airflow it was seeing with the performance filter good luck and have fun!Oh I forgot to tell you that the choke is not really a choke as it doesn't restrict air flow at all rather it pulls fuel straight from the bowl and feeds it into the intake side so it's an enrichment valve if your main jet was to lean and you pull that lever 1/2 way the engine will pick up power as the a/f ratio becomes closer to where it should be!

 

[KoolBreeze420]

Ok, thanks, this was great However I'm still not sure I understand the 2 jets thing. I did move the clip up from its default setting and the carb flooded then I moved the clip down from it's default setting and now it's idling and seems to be a great ride there's no bogging at all.When I hit the throttle she moves like never before the only issue I have I think is that fact that I can't move the choke from the cold start position even after she's warmed up I just rode her for about a mile when I let the throttle go she was idling just fine so I thought she should be warm enough to move the choke but she stalled right away and I don't understand why.
OK, I was rereading what you wrote just now after I already wrote all this I see you're telling me that the choke is not a choke I don't understand.
Can the blue air filter from the CNS carb go on this carb? Do you have any website sources that can help me learn more about this carb cause now the choke is not a choke etc. lol Maybe you can give me a link to a better air filter that will work.

 

[CrazyDan]

You gotta adjust your pilot jet while the engine is warm and unchoked. You have it set super lean so it can run choked. Try richening it up to run unchoked. Or maybe you have an air leak? Spray starting fluid around the spot where the intake connects to the carb and if it revs up you need to fix an air leak.

 

[KoolBreeze420]

You gotta adjust your pilot jet while the engine is warm and unchoked. You have it set super lean so it can run choked. Try richening it up to run unchoked. Or maybe you have an air leak? Spray starting fluid around the spot where the intake connects to the carb and if it revs up you need to fix an air leak.

It seems like you may not have read the reply to me and the reply back to Street Ryderz.
I would have agreed with you until I read what Street said to me. He said that the choke is not actually a choke but is an enrichment valve.
With this new knowledge, the way my engine acts would appear to be normal. The way I understand it now is that when I open the valve it's sending more fuel into the engine flooding it now this would also explain why I have to find the exact setting or the sweet spot with the valve(choke) lever in order to get the motor running so instead of restricting air the lever is actually fine tuning the fuel to air mixture. Currently, the motor appears to be running fine.
With this knowledge, I have to accept that the choke isn't a choke and that it is an enrichment valve.

 

[Street Ryderz]

It seems like you may not have read the reply to me and the reply back to Street Ryderz.
I would have agreed with you until I read what Street said to me. He said that the choke is not actually a choke but is an enrichment valve.
With this new knowledge, the way my engine acts would appear to be normal. The way I understand it now is that when I open the valve it's sending more fuel into the engine flooding it now this would also explain why I have to find the exact setting or the sweet spot with the valve(choke) lever in order to get the motor running so instead of restricting air the lever is actually fine tuning the fuel to air mixture. Currently, the motor appears to be running fine.
With this knowledge, I have to accept that the choke isn't a choke and that it is an enrichment valve.

Any air filter you can fit on it will be better than the stock! And yes it's an enrichment valve and your exactly right finding the sweet spot with the lever gets the a/f mix corrected!So you deffinatly need a richer main and idle(pilot) jet or use micro indexed drill set and drill them out until tuned!

 

[KoolBreeze]

Any air filter you can fit on it will be better than the stock! And yes it's an enrichment valve and your exactly right finding the sweet spot with the lever gets the a/f mix corrected! So you definitely need a richer main and idle(pilot) jet or use micro indexed drill set and drill them out until tuned!

I know it's been awhile since we talked but I got it running fairly well. There was a malfunction and that engine became unrepairable. I have a brand new engine and a brand new bike and am using this carburettor. So yesterday I finally started the new engine for the 1st time and the damn thing took off like a bat out of hell trying to buck me off lol.
I replaced the air filter and all like you suggested does the air filter make that much of difference?
I ask Because this new engine feels like it has about a 1/3d more power than the last one.
Either my last engine was a bit of a lemon or it wasn't a 66cc but a 49cc sold as a 66cc or the air filter is able to provide that much of a boost it's amazing but the engine is revving way too high, I'm afraid if damaging it. This is why I have come to talk to you again.
You said I should start with the needles all the way in. With the screws, all the way in isn't that maximum revs or max speed?
Won't running it high damage the piston rings since they haven't seated properly yet?
Should I maybe use the stock carb for a few hours before using this carb?
My main concern is ruining it at high revs before the piston rings have had time to properly seat themselves. Please, could you or anyone else that may read this answer the questions and maybe give me some other tips.
I also don't think I totally understand what you mean in your last comment that is in quotes of this message.

 

[Street Ryderz]

I know it's been awhile since we talked but I got it running fairly well. There was a malfunction and that engine became unrepairable. I have a brand new engine and a brand new bike and am using this carburettor. So yesterday I finally started the new engine for the 1st time and the damn thing took off like a bat out of hell trying to buck me off lol.
I replaced the air filter and all like you suggested does the air filter make that much of difference?
I ask Because this new engine feels like it has about a 1/3d more power than the last one.
Either my last engine was a bit of a lemon or it wasn't a 66cc but a 49cc sold as a 66cc or the air filter is able to provide that much of a boost it's amazing but the engine is revving way too high, I'm afraid if damaging it. This is why I have come to talk to you again.
You said I should start with the needles all the way in. With the screws, all the way in isn't that maximum revs or max speed?
Won't running it high damage the piston rings since they haven't seated properly yet?
Should I maybe use the stock carb for a few hours before using this carb?
My main concern is ruining it at high revs before the piston rings have had time to properly seat themselves. Please, could you or anyone else that may read this answer the questions and maybe give me some other tips.
I also don't think I totally understand what you mean in your last comment that is in quotes of this message.

To break in the new engine you want it richer so yes maybe use the other carb for a bit or set this one up richer.I had sugguested that if your needle (air screw) was turned all the way in so that it was full rich and it still idles high that the pilot jet is to lean and needs to then be enlarged I think anyway it been awhile LOL.

 

[KoolBreeze420]

To break in the new engine you want it richer so yes maybe use the other carb for a bit or set this one up richer. I had suggested that if your needle (air screw) was turned all the way in so that it was full rich and it still idles high that the pilot jet is to lean and needs to then be enlarged I think anyway it been awhile LOL.

OK, right now I have a new engine and new bike. Right now I gotta figure out what position the idle screws work. Does screwing it all the way in tight mean full or low idle?

Well, I switched to the stock carburettor and the engine runs beautifully lots of power this engine outperforms my last one by a 100%.
Is it possible that the YuanDung carburettor is just too good for this engine?

You see my last bike had a hard time pulling my trailer full of goods up a hill which is between me and the shopping center so I bought a variety of stuff trying to improve it.
This bike is heavier than my last and has the stock exhaust stock carburettor and it climbs the hills like they don't even exist.
I checked out the Yuandung carburettor cleaned it and everything moved the pin clip and it simply won't slow the engine down I had the screw nearly out of the carb and it actually popped the f***ing sparkplug out of the cylinder head I guess I just use the stock one but any suggestions for the Yuandung?

 

[Street Ryderz]

OK, right now I have a new engine and new bike. Right now I gotta figure out what position the idle screws work. Does screwing it all the way in tight mean full or low idle?

Well, I switched to the stock carburettor and the engine runs beautifully lots of power this engine outperforms my last one by a 100%.
Is it possible that the YuanDung carburettor is just too good for this engine?

You see my last bike had a hard time pulling my trailer full of goods up a hill which is between me and the shopping center so I bought a variety of stuff trying to improve it.
This bike is heavier than my last and has the stock exhaust stock carburettor and it climbs the hills like they don't even exist.
I checked out the Yuandung carburettor cleaned it and everything moved the pin clip and it simply won't slow the engine down I had the screw nearly out of the carb and it actually popped the f***ing sparkplug out of the cylinder head I guess I just use the stock one but any suggestions for the Yuandung?

Turning the idle screw all the way in would be very high idle,all the way out is lowest idle and you need to find where it likes to idle between those.The advantage to the CNS carb is that ability to fine tune it,but if your not used to setting up this style of carb it will be frustrating due to the fact thhat each part of the throttle range now has to be set right to get the best out of it,and if that's the case you should just stick with the stock carb it's much easier to set up!For the CNS however it sounds as though the pilot jet is too lean or maybe it's not getting a good seal (air leak) its best to use a 19mm O ring between carb outlet and engine intake to seal it up better.Then you go through the steps of setting it up from idle to w.o.t by jetting,air screw and needle settings and riding it to see whats what,it time consuming but well worth it in the end and then of course it get easier to do once you've done it a few times.