NT Speed or Dax RT?

I vote for the Speed carb. I'm running one on both on my current bikes. I've never actually tried an RT, but I do own one, so I could easily use it if I wanted to. An RT is actually slightly smaller than a Speed carb. An RT uses a highly suspect plactic spacer on the intake manifold like a total pos CNS carb. That alone is probably the number one reason I don't want to use the one I have.

I can compare the difference between an NT, and a Speed carb for you. Compared to an NT, you'll get a better more consistant idle with the Speed carb. Speed carbs tend to not be as touchy about 4 stroking as a NT. You can use the same throttle cable between an NT and a Speed carb, but not an RT. It has to use a different cable. Other than idleing better, and running smoother, any performance gains you realize will depend on your tuning, and other performance modifacations, because a NT carb is already big enough for a stock motor. A Speed carb is a little too big for a 48 cc, so hopefully your motor is a 80. If not, you probably would be better off with a RT or NT.

NT carb........ = 13.74 mm
RT carb........ = 14.67 mm
Speed carb... = 14.78 mm

Risingsunn said:

So what did you end you end up doing about tuning? Do they make different size jets for the Speed or do you have to solder and drill them?

Click to expand...

Of course there are different size jets. NT and Speed carbs both use 5 mm jets sold by Pirate Cycle, and SBP among others.

All my china girl 80s end up with either a 66 or 68 jet after break in. Stock is equal to about a 70. I've only done one thing to my motor that helped the top end a little, and that was opening the exhaust. It's still very quiet, so we're not talking about anything drastic.

I've done several other things to the motor, but they mostly just make it run better, not faster.

Here's a list

Speed carb
66 jet
Shorty intake manifold
free flow air filter
NGK BP5HS spark plug, BP6HS in summer
Copper core plug wire
NGK plug cap
36T rear sprocket

All my china girls with this level on modification will run about 37 mph, which is about 7100-7200 rpm with my gearing, which I consider a little over red line of 7000. You can easily get much higher levels of performance, but your motors life span will suffer greatly. It's a good idea to keep your revs below 6500 rpm as much as possible. 6000 is even better. These motors are designed to have a torquey, wide power band more than a peaky high output, high rpm power band like a Morini motor.

I can get the same level of performance with a NT carb, but it just won't be as smooth, or run quite as well as with a Speed carb. If you want to really utilize the extra performance offered by a bigger carb, you'll need to port your cylinder, install an expansion chamber, and raise your compression. Stuff like that. And buy a spare motor for when yours blows up lol.

I got the RT carb from Dax to replace the stock NT. I had to adjust my engine mount forward to get it to fit. Once I found the right jet I noticed a slight increase in power and speed, my gas consumption went up slightly also. The RT from Dax comes with 5 different jet sizes and I'm pretty happy with the results. Yesterday I put an expansion chamber exhaust pipe from SickBikeParts on to replace the stock exhaust and noticed a huge increase in torque and acceleration with a slight increase in top speed.

Risingsunn---When I say I moved the engine forward what I really mean is that I had to tilt the engine forward. In my first picture above you can see how tilted forward the engine is. To do this I just loosened the engine mounts and move them. The front mount moved about a half an inch toward the peddles and the rear mount a half an inch up toward the seat. Look at the first picture closely and you can see how close the air filter on the RT carb is to the frame. Moving the engine slightly gave me enough room to get the RT carb on and off easily. It's not exactly level and I was worried that the float would be at too much of an angle to function properly but it doesn't seem to have affected the performance of the carb.

Risingsunn said:

Biknut
The main reason I am looking into more power per say is so that I can run better speeds toward the middle of the power band vs having to run higher RPMs for decent speed. Right now I can hit 30 at WOT whereas I would like 30 at about 3/4 throttle. I am going to be getting a 36t sprocket and probably an Arrow pipe here in the next month or so to help out with that too. I am not certain if I would be comfortable with working on porting the engine just yet though. Also do you have any opinions on the Arrow Torquer pipe? I was relying on bigbutterbean's review that it good but a second opinion is always valued too!
Tyler,
Nice bike man! What kind of engine you got there? And what did you use to adjust the engine mount forward? I think I would like to do it just to remove some of the slack in my chain.

Click to expand...

After you get your bike broken in you can tune your bike. Right now you're running too much oil for max power. You need to get to at least32:1. The oil ratio you can run depends on what the oil manufacturer recommends. Generally dino oil runs about 32:1. Synthetic will be 40:1 - 50:1. Changing the oil ratio also changes your fuel mixture. More oil = less gas, leaner. Less oil = more gas, richer. Thats why you should wait till your motor is broken in before tuning.

Risingsunn said:

So WHILE I am waiting...... Anyone know the difference between the standard speed carb and the NT SPEED CARBURETOR GEN 2 MB I linked on my first post here? Just curious.

Click to expand...

Looks like the only difference is the gen 2 doesn't have a petcock, and the fuel inlet sticks out of the side of the carb at an akward angle. IMO they dummied it down.

Yaa, thats what I'm thinking. Okay, so I'm looking at this website :
http://www.motorizedbicycle.ca/aftermarket-parts.html
It lists the NT speed carb Gen 2. Now whats confusing to me is when you guys have been talking, for example when Biknut made his first post on this thread, reading it seemed like he was reffering to 3 different carbs. The NT, the RT, and the Speed carb... Isnt the NT the same thing as the speed carb with the red air filter thing on it thats for sale on this page?

Also, this page has a product called the CNS high performance carb kit. Whats up with that one?

Frogster said:

Yaa, thats what I'm thinking. Okay, so I'm looking at this website :
http://www.motorizedbicycle.ca/aftermarket-parts.html
It lists the NT speed carb Gen 2. Now whats confusing to me is when you guys have been talking, for example when Biknut made his first post on this thread, reading it seemed like he was reffering to 3 different carbs. The NT, the RT, and the Speed carb... Isnt the NT the same thing as the speed carb with the red air filter thing on it thats for sale on this page?

Also, this page has a product called the CNS high performance carb kit. Whats up with that one?

Click to expand...

You've got it right. you just mentioned 4 different carbs. NT, RT, Speed, and CNS.

Don't get a CNS, it's crap. NT is what comes stock on most kits. RT is a low cost Mikuni clone. The Speed carb is a bigger version of a NT, it it's what I recommend.

Here's a link to a speed carb. I've bought several of these.

http://www.ebay.com/itm/181052658109?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Okay sweet, that is the same carb that I have here.
http://www.motorizedbicycle.ca/aftermarket-parts/nt-speed-carburetor-gen-2.html
Im in canada, so by the time i paid for the shipping on the ebay one it would be about the same price.

So the speed carb is the way to go. If I were to get a bunch of other upgraded parts.
For example, im thinking of getting the bikeberry.com flying horse motor in black, then buying a high flow air filter http://www.sickbikeparts.com/catalo...ducts_id=99&osCsid=ncv6fuie48itbr49jn0vkj4t57 a short strait intake manifold from somewhere
a sbp expansion chamber http://www.sickbikeparts.com/catalo...ducts_id=83&osCsid=ncv6fuie48itbr49jn0vkj4t57
Added muffler for sbp expansion chamber http://www.sickbikeparts.com/catalo...ducts_id=78&osCsid=ncv6fuie48itbr49jn0vkj4t57 also noise dampeners http://www.sickbikeparts.com/catalo...ucts_id=140&osCsid=ncv6fuie48itbr49jn0vkj4t57
an aftermarket fuel filter, also a puch hi hi compression head https://www.treatland.tv/puch-70cc-head-p/puch-hi-comp-head-70cc-new.htm
an upgraded CDI ignition box http://www.jnmotorsbikes.com/Jaguar_CDI_p/jnm1195.htm

With all these upgrades would it be important to change my Speed carbs fuel jet size? or should i just not bother with it and leave it be?

does the speed use the same cable as nt???

borntofli said:

does the speed use the same cable as nt???

Click to expand...

Yes, same cable. That's one of the benefits of it over a RT, or CNS. It also uses the same jets.

Risingsunn said:

Frogster,
Buy the engine, replace the mounting hardware, sparkplug, sparkplug wire, run the rest stock. Run a couple of gallons of gas through it at roughly 25:1 mix, THEN look into aftermarket upgrades. There are various opinions on the best way to break the motor in, mine would be don't ride it like a bat outta **** but don't baby it either.

I too was ready to go all out and make my bike a mean machine but after 200 or so miles, I am realizing that I am quite happy with with almost stock. So built your bike, read the forums, learn a lot and have fun with it.

Click to expand...

Thanks risingsun, I think I will end up doing something like that. Advice from experienced people is always appreciated. Unfortunately I was naive and purchased from Aydin Ozan at motovelo before looking into forums and educating myself. Ive currently been robbed 875.97 USD. Aydin is refusing to refund me my money and refusing to send me any of the parts I ordered because I canceled my order when I was getting terrible customer service and my emails inquiring about the status of my order were being ignored for periods up to 10 days.