CNS-v2 vs. DAX RT vs. NT Carbs.

[PerryP180]

This is a non-professional evaluation of these three carbs..
I started with the CNS-v2. After pulling the tube from the bowl to the air filter it ran pretty good. Idled great, descent mid-range, bad 4 stroking starting at about 3/4 throttle. Had some 4 stroking in mid-range but acceptable. Tried the SBP Heavy duty airfilter. Engine would crank, idle good and then die when I would engage the clutch. Just guessing it was too much air flow. Put stock filter back on and it ran fine.
Heard about the DAX RT and thought maybe I could get more performance out of the motor with it. Installed it with the stock #75 jet and the motor had no power and 4 stroked at all times. Installed the #80 jet and couldn't get much above 10 mph with all the 4 stroking. Put in the #70 jet and it finally started running on par with the CNS except it had a little less climbing power. I was getting 1 mph more wot. Still a lot of 4 stroking past 3/4 throttle. This could have all been from a mislabeling of the jet sizes. Out of curiosity I checked the #80 jet. My #68 drill bit(.031) was the largest bit that would pass through it. I lost the #75 jet. One day I'll check the supposedly #70 that's installed just to see. I decided to see how an NT stacked-up against these two. Put it on on was surprised. Very solid low and mid speed with no 4 stroking. Past 3/4 throttle there was a small bit of 4 stroking but not nearly as bad as the other two carbs.. I was very pleased. I decided to put the SBP HD air filter on for the heck of it. I now runs solid through the entire power band. No four stroking at any speed, better climbing power than the other two. The SBP filter made a significant difference. I did lose maybe one mph top end vs. the DAX RT. The engine sounds great with no more four stroking. It will be interesting to see if this stretches my mpg a little. Maybe I just happen to be at the right altitude (@ 800') for this set-up. I just know that the NT with the SBP HD air filter is now my preferred set-up. All of this testing took place over a little more than two months. Take it for what it is, a non-professional opinion.

 

[homejones]

I have the Dax RT Carb. Think I found out recently that it's a Dellorto SHA 15 clone. I had a CNS2 carb originally and couldn't get it tuned correctly. The Dax RT carb worked out of the box and got rid of that choke lever.

I am getting 4-stroking with the RT carb as well. I am on the stock 75 main jet. I live in LA so we're near sea level here as well. As for the air filter, even though I really love the look of the Dax filter, I ordered the original Dellorto air filter as it's low profile filter and is exactly what I need for my tight build.

I'll take any recommendations RE the 4-stroking.

 

[Vistaman73]

The only reason you would get 4 stroking is because it is not tuned right. If you tune the RT carb it will improve performance over almost any other carb. I have the Rt and I have properly tuned it and it makes my bike so much better its not comparable. I run a 68 jet and it runs great, a little rich actually.

 

[PerryP180]

I'm leaning toward the motor just not getting enough air or too much fuel past 3/4 throttle. A smaller jet should take care of that but when I switched to the smaller jet it affected the motors midrange in such a negative way that I couldn't get up to 3/4 throttle. A more free flowing air filter should help but the stock filter looks very free flowing. I may give the DAX RT a try later but I was just so happy with the way the NT ran that I'll use it for a while.

 

[homejones]

Yea, I've tried the 3 jets that come with the carb and they all seemed to work the same. Waiting to empty my tank so I could run a proper 32:1 mix.

Also, I know on the CNS2 carb, you could move the needle clip - can we do that with the RT carb? Where is that located?

My 4-stroking occurs in 3/4-full throttle range.

 

[PerryP180]

There is no needle to adjust on the DAX. The idle screw only adjusts the idle. There is a needle near the hinge on the float. It is my understanding that it is to shut-off flow of fuel to the bowl when it fills. I don't know what else can be "tuned" except to change jets and make sure the slide and spring are installed correctly. I guess you could also double check that the jet hasn't picked-up any trash.

 

[BeaverRat]

The only reason you would get 4 stroking is because it is not tuned right. If you tune the RT carb it will improve performance over almost any other carb. I have the Rt and I have properly tuned it and it makes my bike so much better its not comparable. I run a 68 jet and it runs great, a little rich actually.

Yep, I agree with this completely. When I was running the stock 75 it was almost un-ridable because it was so rich. I stepped down to the 70, and it worked well, but was still 4 stroking at WOT and my plug was a bit too dark. Now I am on a custom 67 jet and it is running amazing. It is so much more consistent and powerful than my old NT carb. Much better throttle response, and the slide is much more free to move than on the NT or CNS carbs (there is no friction at all in the slide). I lubed up the throttle cable, and it feels nearly identicle to a motorcycle throttle.

You can't expect the RT carb to work perfectly right out of the box. I believe it is the general consensus that they run on the rich side, and must have a smaller jet than a 70 to achieve their full potential.

But when you get it tuned, it is a rocket...

 

[droc089]

On my Rt, the plug looked kinda lean. What do your guy's plugs look like that use the 70 or lower, mine just looked really clean..too clean lol.

 

[homejones]

I just ordered a whole set of jets, gaskets, and the original air filter assembly from treatland.tv. Sadly, I spent more on the parts than on the carb, so this whole ordeal is costing way more than I thought. On the bright side, I get to do some proper tuning this weekend.

Also glad I found a new vendor (I have no affiliation with them). You guys should check out treatland.tv. Their shipping prices are really reasonable as well as their part prices. For example, they sell jets for 2.75 a piece while SBP sells for 3.49.

 

[droc089]

Totally agree with you on the money side, way more than expected. The ****face grin from ear to ear every ride is worth it though lol.

 

[PerryP180]

To make sure you know about ordering jets, the higher the number the smaller the jet diameter. #80 jet is smaller than a #75 jet. If a motor is running rich that means it is getting too much fuel. Too lean means not enough fuel.
Jet Sizes and corresponding diameter.
#80=.0135
#75=.021
#74=.0225
#73=.024
#72=.025
#71=.026
#70=.028
#68=.031
#65=.035

 

[droc089]

To make sure you know about ordering jets, the higher the number the smaller the jet diameter. #80 jet is smaller than a #75 jet. If a motor is running rich that means it is getting too much fuel. Too lean means not enough fuel.
Jet Sizes and corresponding diameter.
#80=.0135
#75=.021
#74=.0225
#73=.024
#72=.025
#71=.026
#70=.028
#68=.031
#65=.035

I know my drill bits came in that scale, but the ones I got from DAX where the opposite, the 80 is way bigger than the 70. Either he didn't mark them right or their just different jets.

The 80 looks bigger, and when I use it it 4 strokes and goes slow. The 70 it runs fine but the plug looks way clean and kinda gray.

 

[PerryP180]

My #80 from DAX was a #68 by drill bit. I lost my #75 and the #70 is still in the carb.. At some point I'm going to check it and then call Duane at DAX about it. The jets I got came inside a folded piece of tape with the # written on it by hand. There could have just been a simple mix-up. I checked with a lawnmower shop and to verify that higher #'d jets are smaller diameter. Of course the chinese could measure them differently just like they do the cc's on the motors.

 

[BeaverRat]

To make sure you know about ordering jets, the higher the number the smaller the jet diameter. #80 jet is smaller than a #75 jet. If a motor is running rich that means it is getting too much fuel. Too lean means not enough fuel.
Jet Sizes and corresponding diameter.
#80=.0135
#75=.021
#74=.0225
#73=.024
#72=.025
#71=.026
#70=.028
#68=.031
#65=.035

No, that is incorrect. The higher the jet size number, the bigger the hole size is. A #70 jet has a .70mm hole. A #75 jet has a .75mm hole.

What you were referring to is the drill bit numbering system. For example, a #65 drill bit is quite different from a #65 jet. We use the # drill bits when a custom jet is made to size. If you want a #67 jet (.67mm) you must use a #71 drill bit.

There are 3 ways of describing a jet: the jet number, the drill bit number used to create the hole in the jet, or the actual size of the hole in mm or inches.

The jet # just means that number in hundredths of millimeters is the size of the hole...

I hope that made sense.

 

[PerryP180]

No, that is incorrect. The higher the jet size number, the bigger the hole size is. A #70 jet has a .070mm hole. A #75 jet has a .075mm hole.

You are correct. I found this chart that shows the #drill bit to corresponding jets.
jet size
60 #73 bit size
65 #71 approx.
70 #70
75 #69 approx.
80 #68
85 #66 approx

 

[Ghost0]

Don't get drill size designations mixed with actual sizes. Jets are sold by their size in mm. So a 70 jet is .70 mm which is not the same as a #70 drill.

So a 70 jet is .70 mm or .0275 inches or a #70 drill, what did I contradict myself? No, it is just that the 70 designation just happens to be one that is the same across the board. Lets try it with a different number. So a 75 jet is .75 mm or .029 inches or a #69 drill. Lets go the other way, a 60 jet is .60 mm or .0236 inches or a #73 drill. Hope that helps.

 

[Ratchetbirds]

Uh silly question here, one of you guys sez .70mm and the other sez .070mm. Just curious as to which is correct.

 

[timboellner]

#70 jet is .7mm not .07 mm

TiM

 

[BeaverRat]

Delete please... it posted twice for some reason

 

[BeaverRat]

Uh silly question here, one of you guys sez .70mm and the other sez .070mm. Just curious as to which is correct.

The other guy was correct ha ha... Remind me not to answer questions at 2 in the morning

BTW I fixed it in my post...