Inside the 2010 Grubee Skyhawk CNS Carb

KCvale · Nov 5, 2010

I recently got my 1st 2010 Grubee Skyhawk motor kit in, and while I went through the carb to see the differences I took some pics.

These carbs are nothing like the 2009 or earlier carbs so I’ll just take you on a sight seeing tour.

It is officially a YuanDung Skyhawk C-32CNS66-EPA.

One thing of note is the lack of a fuel petcock valve.

Another is the plastic gasket to seal the intake.
It seems prone to breaking.

I do like the new floats, but still somewhat baffled with the new ‘choke’ setup.

It seems to be a secondary jet to draw raw fuel into the carb if you open the plunger.

(Continued below)

KCvale · Nov 5, 2010

{Continued from above)

I couldn’t get a good pic of the inside of the ‘choke’ chamber, but it opens a vacume passage to the main carb body to that bowl tube, but it’s just raw un-atomized fuel.

This is the carb cable top piece.

And this is how I mounted it to keep it out of the way.

So how did it perform on this 48cc?
Like crap.
All GasBike could tell me was ‘Mess with the adjustments’.
If someone has some tips for adjust this carb for a dry warm low altitude area like Phoenix for a 48cc Skyhawk I could sure it.
Near as I can tell it running way to rich as the plug is oily wet after a gutless ‘kinda runs’ ride.

riff44raff · Nov 6, 2010

hows the resi of the kit ?? do you know who ships the gt5 to california ??

KCvale · Nov 6, 2010

Cool, thanks for the info, I updated the pics.

The other kit changes is a heat shield on the tailpipe which for most beach cruisers hits the pedals. Thats OK, it is just two screws to take it off.

The CDI has beefier screw mounts and longer screws that actually fit a fat front tube.

Other than a real gas line, I don't see any other differences.

------

Thanks again on the separate idle system, I know where to look for my problem now.
It idles great but bogs like crazy and soaks the plug when I try to accelerate.

What the heck, since I am messing with it now I'll snap a pic.

-----

This is the carb plunger and lean/rich adjustment.

If I am not mistaken the old carb's only had 3 adjustments and this has 5.
It also looks like it comes set at the second leanest setting (2nd notch from top).

That might explain my bogging problem, not enough fuel with the air.
I'll move it down a couple and see ;-}

KCvale · Nov 6, 2010

Great call Nougat!

OK, stock idle was set 1 full turn open.

I got it warmed up with the choke and this is what works idle wise for me.

Phoenix, 10:15 AM
67°, 27% Humidity, Dew Point 32°, Pressure 29.91 In, ~1200' elevation.

Warmed up, choke off:
3/8th of a turn for idle mix.

I now have full throttle.
Note while I had it open I leaned the main to leanest (top notch) and I think that is why it seems a little gutless and the plug was bone dry and white.

I'll mess with the mix and go from there.
Thanks again, and hopefully this will help others as well ;-}

KCvale · Nov 6, 2010

No joy moving the clip down, she'll only run all the way up.

Skarrd · Nov 6, 2010

i'm in about the same situation. it'll run up to around 29mph and act like it's hitting some type of governor...

i've got my idle speed screw at 4.5 turns out, and my air mix at 3.5 turns out, needle at #1 notch. (was fouling the plugs at #2) also running gas mix of 24:1 right now...

Skarrd · Nov 6, 2010

Nougat said:
Skarrd: 29MPH is exactly what you should expect from a stock kit. It feels like it's hitting a wall because it is. A little two stroke isn't going to rev forever.

If this is a relatively new build, 29MPH is great, and you should expect to gain a little more power and speed after break-in.

What does your plug look like?

sort of a grey-ish black. like between medium and dark black. it runs great and pulls hard, just felt odd how it would keep pulling then suddenly stop accelerating...

i may see about trying to port match the exhaust pipe a little better...

GearNut · Nov 6, 2010

Here's a link to carb tuning instructions for a carb that is nearly identical in operation.
It is for a Kawasaki KDX. Do not be fooled by it's lack of an enrichment circuit like the new CNS carb has. The basic air flow characteristics, jets, air screw, needle, ect are identical to the new CNS carb. From idle to WOT it works and tunes identically.
carb tuning

cory151 · Nov 6, 2010

I just assembled a 2010 66cc with a CNS and its also pretty gutless, although I feel it could be the fact that I clearenced the the muffler slightly, to fit the frame. Im wondering if ripping that substrate out of the muffler would cause an increase in performance.

biknut · Nov 7, 2010

Nougat said:
Skarrd: 29MPH is exactly what you should expect from a stock kit. It feels like it's hitting a wall because it is. A little two stroke isn't going to rev forever.

If this is a relatively new build, 29MPH is great, and you should expect to gain a little more power and speed after break-in.

What does your plug look like?

I guess I doing pretty good then, because that's exactly how my bike runs. It pulls up to about 29 then feels like it hits a governor and backs off about 1 mph. Mine looks like it's probably running a little rich so I just dropped the jet down one size to a 68. My 48cc is just running the standard carb though. Doesn't sound like there's much advantage from the new carb.

KCvale · Nov 7, 2010

Nougat said:
...but you're saying it doesn't run with it there? Doesn't run at all, or just doesn't run faster than idle? I'm torn between the plug gap being too narrow and the float riding too high in the bowl.

It won't run over idle (bogs) on anything but the 1st notch.
I gaped the 3 prong spark plug legs at.025 each.
I don't think it's the float adjustment, I get nothing out of the overflow and no drips, but the carb is mounted at a forward angle...

I tried another CDI and also another 3 prong plug as well as an Iridium B6HS plug with no change.

I also checked the choke plunger, it fully closes and opens smoothly.

One note is I am not using the 2010 EPA pipe, I have a chrome muffler with no CAT in it.

Skarrd · Nov 7, 2010

i think the main jet that comes with the carb is too big for our needs.

i know these engines are tiny and can only put out so much power, but it shouldn't feel like it hits a governor when it runs out of power.

KCvale · Nov 7, 2010

This is a handy illustration of what mixture parts do what in relation to throttle position.

I have this topic going on my forum here KC's Kruisers - Motorized Bike Forum - Inside the 2010 Grubee Carburetor as well so I am getting a good crash course in how these new carbs work ;-}

cory151 · Nov 7, 2010

Ok since Im experiencing the same carb bogging issue I decided to take some video so that everyone can see whats going on.

YouTube - Bogging.MOV

cory151 · Nov 7, 2010

Nougat said:
cory151: Oh that is totally float height. Tweak the float tang a bit, so that the float allows more fuel to stay in the float bowl. I bet this is KCs issue, too.

Thanks for the video! Much simpler to figure out than plain old text.

Really?

So which direction do I want it? The float higher or lower in the bowl?

Thanks by the way

cory151 · Nov 8, 2010

Anybody, know which way I should bend these floats? Doesnt seem like theyll go up anymore.

Im pretty close to buying an NT carb.

KCvale · Nov 8, 2010

Nougat said:
cory151: Oh that is totally float height. Tweak the float tang a bit, so that the float allows more fuel to stay in the float bowl. I bet this is KCs issue, too.

You need to check the bowl before adjusting it. If anything mine had too much fuel.

Loosen the manifold mount screw and take off the top cable piece.
Open the gas valve to fill the bowl.
Close the valve and remove the gas line from the carb.
CAREFULLY remove the carb keeping it level, and hold it so you can keep the bowl on while you remove the 4 bottom screw with the carb still upright.

If you get gas coming out when you remove the last screw like I did your float level is NOT too low.

The adjustment tab is here.

It is that center piece and connects to the pivot bar and open on the other end. Push it down to lower the gas level, up to raise the gas level.
I bent mine down a tad just in case it was a fuel overflow problem.

So far though, the top leanest needle setting is all that will work.

cory151 · Nov 8, 2010

Thanks for the info Im gonna give it a shot. Ive tried all 5 settings on the needle with little or no change.

KCvale · Nov 8, 2010

Still no joy here.
It bogs when the main jet kicks in regarless of needle setting or idle mix.
I marked the throttle, here's a video.

YouTube - KCbog.avi

I need to send this POS carb back.

Inside the 2010 Grubee Skyhawk CNS Carb

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