I'm in the market for a new carb

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Rusty1

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Jun 12, 2012
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Right now I'm running with the stock junk CNS carb that came with my kit . I've done everything possible to make this thing run right and its just never ran to its potential . There are no mixture adjustments on the CNS so its impossible to do anything but adjust your idle . My motor came from the factory with a head that had a cross threaded spark plug and sucks air so it has to be replaced . While I have it tore down to fix that I want to replace the carb and intake to something that's going to give me more option to adjust it and better performance . I've narrowed it down to either the RT or the NT carbs with a shorter straight intake rather than the offset intake that came stock with the kit . I know I'll probably get a few different opinions on this but that can be a good thing . Which is the better carb and will I need to order a new throttle cable for it ?

I guess I should have mentioned .This is a 66/80 Grubee SkyHawk
 
2door

2door

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Want reliable, troublefree performance? Stick with the old classic NT. It doesn't have any mixture adjustments, you do that by jet size, but all they ask is to be given clean fuel and they will work. I've personally never owned a CNS and judging from all the negatives I've read here, I never will. I've tried other carbs but always come back to the NT. And, they're cheap. Just one more opinion. You'll get others.

Tom
 
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Rusty1

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Thanks 2door . So far that's the direction I'm pointing . Do you know if I need a different throttle cable ? I'm going to order one or the other today and I don't want to make another order and wait for delivery twice .
 
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Rusty1

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Also guy's . I know I'm a bit of a pest but do you know if there is any performance difference between the slant head and the straight ?
 
Dave31

Dave31

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2door

2door

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Rusty,
I don't believe the cables are compatible. You can always make your own but if you just want to bolt it together I'd order a cable for the NT as long as you "have your credit card ready", as they say on TV. :)

Tom
 
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Rusty1

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Thanks guy's . I decided on the NT . Its a simple and proven set up . I also went with a straight plug rather than the angle fire . There again its a tried and true set up . I don't need the bike to be fancy I just want it to run properly so I figured I would try to keep it as simple as possible .

Rusty
 
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Rusty1

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Dave your suggestion to read those post's gave me a lot of insight on the subject and Although They are posted here I don't know if i would have found them on my own . THANKS A BUNCH !

Rusty
 
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Rusty1

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OK guy's , I got my parts in yesterday . I ordered an NT carb and a new head , I went with the straight plug . It cured my spatter problems all together . Now its a dog at take off and Ive lost a lot of top end . I'm sure its just a matter of moving the pin up or down or going to a different jet . Any suggestions ?
 
2door

2door

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Rusty,
How many miles/gallons of fuel has the engine seen? My advice is always to break in an engine completely before worrying about performance. That can be a while and these little Chinese wonders seem to mature with time. They run better and better the more miles they accrue.

If however you have a couple of hundred miles and have burned several gallons of fuel, start reading that spark plug. It will be your best advisor as to what the engine needs. Too light in color and you're lean. Too dark, or black, and you're too rich.

Remember also that with the NT carburetor that the needle only controls fuel flow to about 3/4 throttle. Anything above that the flow is based on the jet orifice size.

Good Luck

Tom
 
Huffydavidson

Huffydavidson

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Jan 29, 2012
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If its run in,then read your plug. The cables on the CNS & NT are the same. I upgraded to the RT and I love it. Comes jet kit . Good luck.
 
crmachineman

crmachineman

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May 24, 2012
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Mee too!
I've been trying different carbs. too. I'm still undecided on what is the best for maximum power. I too have played with the CNS and have had nothing but trouble. The best results have come from the simple, stock NT "speed" carb.
I have also been playing around with the RT dellorto clone, and although it seems to run the engine very well, it's a little anemic. I think it's a little more restricted than the stock NT carb. I'm spending all this money on fancy carbs. get frustrated, and end up putting the pathetic little stock carb. on and it kicks every other carbs. ass!

The only one left to try is the Mikuni. There's a VM 16, but how about the VM 18? does anyone have any feelings about going real big? I have a feeling the carb. is my bottleneck.

.xx.

-Fred
 
2door

2door

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If the carburetor is your "bottleneck" your spark plug will tell you. If after everything the plug is too light in color then you need more fuel than what's being delivered. If the plug is dark installing a bigger carb isn't going to help.

Tom
 
crmachineman

crmachineman

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May 24, 2012
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Really?
Well, the mixture is excellent. A nice tan color. I'll keep your recommendation in mind for sure, but something about it doesn't seem to make sense to me though. ..
Doesn't the color of your plug just indicate what air/fuel ratio is? What I'm thinking is small diameter carb. will be a restriction to air flow. Sure it could have the ability to be jetted/adjusted to deliver correct air/fuel ratio.
Don't you think a large diameter carb., acting as less of a restriction could also be jetted/adjusted to deliver correct air/fuel ratio, right? Why not?
I mean, sure, I could see a drawback to having a large diameter carburetor; maybe it wouldn't idle very good, or also could have bad low speed performance when at full throttle due to lower air velocity at the fuel jet, causing poor fuel atomization perhaps.

Well, eventually I'll probably try some kind of big carb. and find out the bike runs like crap, then I'll say, "Tom, you were right! I just wasted a couple hundred bucks on that experiment!" Then, once again, put the stock NT carb. back on the engine.

The thing is, when I read up on all the performance moped and scooter mods. people are doing, I've noticed 20 MM carbs. being fitted to 50cc engines and I wonder, can the china girls get larger carbs. too?

.duh.

-Fred
 
biknut

biknut

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Sep 28, 2010
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I like the Speed carb better than the NT. The NT has a little better throttle response on the bottom end, but is touchy about 4 stroking on the top end.

The Speed carb has the best top end, and is even easier to tune than a NT. Actually about the same tuning.

The Speed carb has a bigger venturi than either a NT or a DAX carb.
 
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Rusty1

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I bought the low end NT carb from Dax . Although it runs soooo much better I'm still not totally satisfied with it . The motor came with a warped angle fire head that had a cross threaded spark plug in it so I replaced it with and straight plug head . Before replaceing the head I put the new carb on and took it for a ride so that I had something to compare to when I changed the head . I've read quite a few post's discussing the difference's between the straight plug and the angled and wanted to see for myself . I lost both bottom end power and top speed with the new NT . But after replacing the head I gained a little [but not all] of both back . From this point on I will definitely be staying with the straight plug head . It just seems to run so much cleaner and smoother with it . My plug has gone back to being a little on the black side which tells me a new jet may be in order , only problem is I cant seem to find where to order them from .
 
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Rusty1

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PS guy's . Sorry it took me so long to get back here . I've been working super hard to get ready for this weekends pool tournament and just haven't had time to log in .
Thanks a bunch for the help !
 
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