Nt Carb tuning

[SavageBlunts904]

Okay here it is.

I have a 48cc Motor and just replaced the cns v3 carb with a standard NT carb. 100% increase in performance already. But i have read that most of these carbs are jetted to run on a 66cc motor.

I am ordering repair parts and gaskets. upgraded bolts. tryin to get my ride as good as i can. I would like to order some new jets as i am not to sure about redrilling a carb jet. maybe one day.

also a link to a nice carb tuning thread would be nice.

What size carb jets should i get, i know the screw is 5mm.

 

[Bikeguy Joe]

If it runs 100% better, why do you think you need to re-jet, or tweak the carb?

How does it run now? Does it four stroke when at WOT? If not, you are likely fine.

How does the plug look?

Does it start well?

No one can tell you "what jet to get" if you haven't addressed these questions.

Just curious.

 

[SavageBlunts904]

As im climbing to 22-24 which has been about my top speed going down hill with the cns carb the motor over revs like crazy and scares me how much it vibrates. lol The power band still does not kick on. Well it does as the fuel line runs out of fuel right before it runs out.

It starts just fine with out any choke.

the plug is very dark. almost black

 

[Bikeguy Joe]

http://www.google.com/cse?cx=partne...ef=#gsc.tab=0&gsc.q=nt carb tuning&gsc.page=1

Also, not much to tuning an NT...if it runs in a rich four cycle at WOT, you'll need a smaller jet. If you do a WOT plug chop, and it's white, bigger jet. You location (elevation) and other factors will make for a bit of experimenting.

If it is too rich or lean (look at the plug) from off idle to 3/4 throttle, change the clip. (Move the clip up to make it leaner, down to make it richer.) There is no low end, or "idle" circuit to adjust.

Then, there is the art of fine tuning with the gas to oil mix ratio...

 

[Bikeguy Joe]

Hmmmm, not sure if you find a "power band" with these engines.

 

[Bikeguy Joe]

From your description, it sounds like you are pretty close to good. Have you moved the clip either way and tested the mid range?

 

[SavageBlunts904]

okay china made got it. heard it 100 times already. when the motor works to perfection and grants more power because it is firing perfectly. thats my description of a china power band. lol aint like this is a honda cr80. lol im just going to order 5 different sizes. but would like a nice link to a guide to carb tuning.

and yes i did move the clip from the middle. to the 2nd one up. which is one notch. seems nice but need more tests to find out Exactly

 

[biknut]

I know where you're coming from. I tuned a bike with a CNS carb. Stock it would only run about 12 mph. Running twice as good as that isn't saying much. Buy a 66 and a 68 jet. Try the 68 first. Stock is about = to a 71 which is always too rich.

The Atomic BB is 48cc and runs a 68 jet in a NT. The needle clip is second from the top. It tops out about 28-30 mph with a 40T.

http://www.youtube.com/watch?v=9wEGD5mjZPk

 

[biknut]

I've also had good luck with a NGK BP6HS spark plug

 

[Nashville Kat]

You need a smaller rear sprocket if the motor's running better- then it won't scream so much to get a good cruise speed- I'm getting probably a solid 25 mph with a 39 sprock- The speedo's on the other one-

but the motor will run better if I finally get around to changing the cylinder head and putting on a billet intake- got a new NT66 carb ready- and I may go even smaller on the sprock- but this is with lighht narrow 700c wheels and tires-

I dfon't need the same speed the 66 will turn but I think I can get a steady 30 out of her, when it gets there on the flat.

 

[SavageBlunts904]

Thanks for the tips. Biknut you provided what I was looking for. And kat I am running a 44 tooth. I figured I would need a larger one since I weigh 320. I really want this motor to wind out instead of over revv

 

[Greg58]

Savage did you say it runs better right before it runs out of gas? The float level may be too high, since you are at sea level you may try adjusting the float first. I have a nt on one of my bikes with the jet drilled to a #70 bit size, plug color is correct and it tops out at 29 on flat ground. I'm at 900 FAS.

 

[LaLongueCarabine]

My bike has run very well until 2 weeks ago. I found that at WOT I would have a real bad oscillation, power then deceleration. I played with the stock carb but nothing seemed to help. I got an NT and now I've got low and medium acceleration I put everyone in the dust but I top out at 24-25 and everyone passes by like I'm going backwards. UP hill I lose power not enough to peddle but enough to notice and it used to never happen before.
plug color is good, chocolate with the electrode surfaces clear and clean.

I drilled the jet out to .73mm and I did get some improvement but it seems like I need more. So I've just got, .74mm, .76mm, and the biggest .78mm.
Wish me luck finding the right one.

PS does the pin and e-clip do anything? I've moved them up and down with three different carbs and I get worse and not so bad and end up putting it back in the center position.

 

[sputterputtBAM]

.73-.78 Wow, consider spraying the brake cleaner around to see if your getting unmeasured air intake.

 

[LaLongueCarabine]

first thing I did and replaced a torn inlet gasket and tightened the carb clamp (blew off on a test ride.) I also doubt the the same symptoms would be in three different carbs (all had stock jets. until I drilled out mine)

 

[timboellner]

You're going way too rich.
68 or 70 is about right.
I can't believe its not 4 stroking at full throttle.
You need to do plug chop after a long full throttle run
Pull the clutch in and shut it down immediately and let it cool before yanking the plug out.
I'm not convinced you have a clue what you are doing screwing around with the carb jetting.
BikeguyJoe gave you good advice way back in this thread.


Look for an air leak around the carb clamp, or intake gasket.
You also may have a bad crank seal which is another source of an air leak.

What kind of ratio are you mixing your 2 stroke oil?
Believe me I had fiddled many hours in the last several years with the NT carb. Even on my modified 66cc engine anything over a 72 jet is way too much.
Good luck
TiM

 

[SavageBlunts904]

Your right about that I do not know about carb jetting or sodering and redrilling, I e why I posted the question, I have gotten the carb sealed to the engine now and picked up 5 mph. I can now cruise at a solid 23 at half throttle. Yet at WOT ithe motor bogs a little. Getting closer. Also the plug is looking good. Once my package gets here ill be changing the jet to a .68 then ill try.a .66

 

[LaLongueCarabine]

You're going way too rich.
68 or 70 is about right.
I can't believe its not 4 stroking at full throttle.
You need to do plug chop after a long full throttle run
Pull the clutch in and shut it down immediately and let it cool before yanking the plug out.
I'm not convinced you have a clue what you are doing screwing around with the carb jetting.
BikeguyJoe gave you good advice way back in this thread.


Look for an air leak around the carb clamp, or intake gasket.
You also may have a bad crank seal which is another source of an air leak.

What kind of ratio are you mixing your 2 stroke oil?
Believe me I had fiddled many hours in the last several years with the NT carb. Even on my modified 66cc engine anything over a 72 jet is way too much.
Good luck
TiM

Thanks, done a plug pull and it's a nice chocolate color, seems perfect not over rich and certainly not lean. My brother agrees with you that I'm going too rich. I don't think it's 4 stroking, but maybe I'm misidentifying the bogging.

Found the air leak in the previous post but didn't help, (so it wasn't really leaking only looked like it might.)

Oh yeah the mix, still on 20:1 cuz my brother blew up his first motor and we share gas.
I think 40:1 is going in the next tank.

(Note I've tried stock carb stock jet and it bogs at WOT, measured at .68mm with a drill bit.)

The drilled out jet has given me the best performance so far.
I might want to play with the jets only after the new mix?
I will order the rest of the set stock down to smallest.
I did get some improvement by removing the air cleaner, and how bad it that?

 

[Greg58]

If you are running a new motor you may need to wait till you get two to three tanks of break ln mix used before you start changing jets. What most will tell you is do what you have done, get the plug color right, get it to idle and then just ride. It will get better and gain power after a few hundred miles, at about three hundred my first bike started running a lot better.

 

[Greg58]

Everyone of these engines are "different ", some need larger jets than others. You have to learn how to read the spark plug and the sounds the engine makes to get it tuned. I tuned a cns2 Saturday that needed the main jet at a #70 drill size, mine on the other hand I have at a #64 drill size. Both engines are identical, 48cc grubees. I know mine sounds rich but its not, it runs great and will climb hills with ease and tops out at 31 on flat ground.