Best overall 66 cc carb?

Davezilla

New Member
Mar 15, 2014
2,707
5
0
San Antonio Texas
I was liking the NT speed but I don't like that fuel shutoff valve built into the inlet. the problem I've been having is that the inside of this valve has a cheaply made rubber disc with 4 holes in it, 2 of the holes lock it into position and the other 2 are for fuel passage.
What hapens is when the valve is used, it sheds off some of this rubber from the disc and it makes it's way to the needle and seat valve and the main jet blocking it from passing fuel.
I found the problem first time I was about a mile from home and noticed the engine cutting out but when I rolled back off the throttle it would clear up and run right, I was able to baby the bike home, took a look at the fuel filter and it was good as new, pulled the float bowl and it was perfectly clean, removed the fuel shutoff valve, and there it was... lots of tiny chunks of black rubber.
I also noticed there was no flow into the carb past the needls and seat when I put the valve back on so I took the valve off and sure enough... more rubber pieces and I saw where it was wearing off the disc in the shutoff valve.
The fix here is to remove the shutoff valve here and replace with a 8mm banjo fitting, you can also just not use the fuel shutoff valve at the carb as I see no point in having it there when there's a valve on the tank.
Other than the speed carb, I like the Mikuni VM16 and VM18 for a mildly modified engine since it can be fine tuned beyond just swapping the main jet and adjusting the idle speed, the Mikunis also run a slow jet with an idle mix adjust screw so tuning can be done much more accurately.

I also like the floatless carbs like the Walbro or Tillotson carbs, these are great for their tuning ease as well as there are no floats so the carb can run in any position.
 

xseler

Well-Known Member
Apr 14, 2013
2,883
125
63
OKC, OK
I think I've got my CNS V3 carb figured out..........well, at least to my neighborhood hop'n satisfaction. Not gonna change it until it fubar's and I can't fix it. Mid-range is good and very little 4 stroking since I put in a smaller jet and went back to my straight custom exhaust.

(Just make sure you remove the brass plug to access the 'hidden' adjuster.)
 

sub66

New Member
Apr 25, 2014
140
0
0
canada
i like my walbro hda-48 w a wt lever spring bringing the popoff to a cool 10psi and butterfly idle corrected. im seeing great performance of 6000-8000 rpm reeded and boost ported 66cc.
 

BonusParts

Member
Nov 28, 2012
168
0
16
SE-PA
Ive run a cns v3. Junk. Super tempermental even after rejetting. 3* threw the mix.

I presently run an NT speed. It hauls but limits to about 8000rpm just due to volume restriction. And i have also ported the carb too....

Hoping to switch to the mikiuni i have on the bench. Vm18 ought to open it up a good deal
 

Big G

New Member
Jun 25, 2014
18
0
0
Palmdale CA
I have used NT, NT speed, CNS and Delorta 15/15 on a 66 cc with ported Arrow cylinder and high compression head with an arrow pipe w/ expansion chamber. I threw the CNS away after spending a lot of time oin it, never could get it right. The Delorta needed re-jetting out of the box to a 66mm, the stock jet isn't even marked but it was big. I played with the jet a little up, a little down and played with needle position. It runs out ok but I just can't get it to stop breaking down at top end. The original NT that the Grubee motor came with seems to work best overall. The speed carb is just about the same as the original NT. I read post that suggest a lot of grinding this off and sliding that up or down and repositioning the needle etc. In my view, it's just a lot of wasted time doing all of that. Even if you are able to fix a problem, it just ends up running minutely better than the original NT..flg.http://motorbicycling.com/images/smilies/flg.gif
www.arrowbikes.com
 

Big G

New Member
Jun 25, 2014
18
0
0
Palmdale CA
I really like it. Once you get it jetted right, 66 or 68, even a 65 in some cases, and get rid of the very restrictive air fillter, it gives a smoother and faster acceloration because of the flat slide instead of the barrel. I don't know why they install that filter knowing full well that the carb isn't going to work with it. The NT is good too overall it just doesn't allow the motor to run a smooth at high rpms as the Delorta. Throw your CNS away if you have one. All of them work better with the shortest intake possible on you bike. The good thing about the Delorta is that it will work well at an angle unlike CNS and NTS.
 

Davezilla

New Member
Mar 15, 2014
2,707
5
0
San Antonio Texas
that's nice to know because I just got a Morini engine in that has a genuine dellorto Sha 14 14 so my plan here is to jet it down to a 66 and see how it does on my setup.
Of the carbs I've got over here, the NT Speed carb has performed really well but with constant fuel valve issues I replaced it with a PW80 carb, which is the same as the CNS. This one did good but took a lot of tuning to get the bottom end mid range, and top end to all work right at the same time... it's a good carb, but it takes a LOT of tedious adjusting and tuning before it'll perform.... This has been the best overall carb for my setup, but the gains compared to an NT Speed are almost not noticeable other than excellent idle quality.
I've tried the NT carb so I could stay riding when I was waiting on jets for the other carbs and surprisingly, this carb is a very good "all around" carb, it's simple, reliable, and it can parform well on a mild engine. This is the one I'll recommend to anyone who's just starting out and wants to ride more than they want to mess around with jets, needle settings, etc. For the most part, this is a true bolt on and go carb.

For the Dellorto SHA carb, I'll see how it goes and if it can perform better at high rpm I'll keep that one installed... I can always get another one for the Morini engine before I'll have a bike to put that engine in...
 

mew905

New Member
Sep 24, 2012
647
2
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Moose Jaw
I run a 19mm PHBG with a 19mm intake manifold (that's I.D., O.D. is 1" :D ) Didn't need to be rejetted out of the box but I imagine it runs a tad rich. The fun part is there's so much room to open up the slide that when it 4-strokes, you just give it more throttle, and you never seem to run out of throttle :)
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
10
38
N.M.
That 19mm PHBG tuned right IME Should 4 stroke at full out WOT on a level plane. Back off the throttle a tiny bit and it will clean up with the motor and bike speeding up a tiny bit when it happens. The same said carb will not 4 stroke climbing a hill at WOT.

4 stroking not typically happening ever under a significant load. Stop then go or climb a hill etc. PM me if need be I can tell you more. Comes with trick questions lol.
 

rogergendron1

New Member
Sep 18, 2013
882
1
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38
woburn ma
same here with the yamaha pw80 carb... its a lot better quality made cns v3 carb

its better quality vs the cns make it easyer to tune than the cns but still not for a beginner and at just about 16mm its damn near the perfect size for a hevily modded moor IE: im running 13:1 comp puch hi hi head with a decked jug and a .016 thou head gasket and a top end ported jug around 160 deg exhaust and a wide exhaust port thats near 60% the cylinder bore intake at 120 deg and transfers port matched to the case and cleaned up and reangled to the intake side and a 4 foot 1 in strait pipe exhaust that goes over the motor.... with this set up i reach 40 easy on a 44 t rear and the carb took a lil bit to dial in but it was not that big of an issue for me at least

i find the idle perfect even with loads of intake duration for a piston port and only a slight four stroking on level ground... other than that its very responsive and if i try to swap back to the nt carb... LOL ... it cant even flow enough fuel and air to get me over 7,500 rpm !!! and it wont idle with 120 deg intake duration and i need to drill out the main jet massive amounts just to get it to get me to 7,500... and once its tunned to that thers a wierd flat spot of idle to 1/2 throttle that is impossable to tune out because the tunnability is not there and the carb is far to small for my aplications .

the pw80 aka the better quality cns carb can be tunned to work with motors from bone stock to wiledly modded and it has no prblems keeping up

best part is its cheap !

only problem is one really needs to know how to properly tune a carb to get it dialed in .... if you dont know all the little nuances of tunning your going to have flat spots and four stroking all across the board but i assure you its a lot better performing than any other low cost option or stock carb out there once its tunned
 

xseler

Well-Known Member
Apr 14, 2013
2,883
125
63
OKC, OK
Sorry for the stupid question but I don't know what 4 stroking means. Can you tell me please?

When a 2 Stroke engine is running too rich on fuel it will start firing every other stroke rather than on every stroke, you know it's 4 stroking when power is down and the engine makes a blabbering sound rather than a steady buzz.

It sounds like what you will need to do is reduce the size of the main jet in the carb and once you get that right you'll likey see the power go up and the engine will run like it should.

map



Above explanation by mapbike.

Good luck!!
 

mew905

New Member
Sep 24, 2012
647
2
0
Moose Jaw
I like to describe it as "if you sound like a lawnmower".

It's not necessarily jetting too rich that causes it, but it doesnt help the situation. Normally 2 strokes 4-stroke because they cant breathe, having the mixture off only makes 4-stroking easier. check the link in my signature.
 

BjevonT

New Member
Oct 2, 2019
1
0
0
34
I have used NT, NT speed, CNS and Delorta 15/15 on a 66 cc with ported Arrow cylinder and high compression head with an arrow pipe w/ expansion chamber. I threw the CNS away after spending a lot of time oin it, never could get it right. The Delorta needed re-jetting out of the box to a 66mm, the stock jet isn't even marked but it was big. I played with the jet a little up, a little down and played with needle position. It runs out ok but I just can't get it to stop breaking down at top end. The original NT that the Grubee motor came with seems to work best overall. The speed carb is just about the same as the original NT. I read post that suggest a lot of grinding this off and sliding that up or down and repositioning the needle etc. In my view, it's just a lot of wasted time doing all of that. Even if you are able to fix a problem, it just ends up running minutely better than the original NT..flg.http://motorbicycling.com/images/smilies/flg.gif
www.arrowbikes.com
I am having my first experience with the speed carb and so far ive had to do very little tuning. My plug color is perfect, and my bike is running great at all speeds and throttle positions. Want to get the vm18 but not sure because my speed carb has showed no signs of causing any difficulties. My hp will supposively go up .85 if I get the vm18. My current hp is at 3.9, but with the vm18 its said to raise my hp to 4.75. Is it worth the swap? Does more air intake really improve performance?