OMG I have to tune a CNS!!! Help

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Sanction

New Member
Jun 1, 2011
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Central Florida
Here is a little info on where to get the Machinists bits.
21 Pc Mini Drill Bit Set #61-#80
Price: $7.75 w/free shipping


What kind of solder should be used to fill the jet if need be? And just how should that be done?
Maybe a few pic's of the jet being drilled, the float settings, C-Clip, etc. etc...

Before long this thing is gonna resemble a how to manual!
LOL!!!

Great job everyone!
 
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rustycase

rustycase

Gutter Rider
May 26, 2011
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Left coast
This is a GREAT thread!

from biknut
"It's not all love and roses though. I have yet to mess with the low speed much yet. Right now it starts Ok, Idles Ok, and accelerates OK, but it has a nasty little spot right off idle. If you give more throttle it goes away. I think it 4 strokes there too."

Try the small square filed at the down-stream side of the slide to let in a bit more air during the transition from idle in through mid range.


from brandon's WILD phone video!!! (I ain't young any more!) ..at mid range there was a lot of 'burbling' at mid range... 4 stroking... needle is wrong.

Same thing as biknut... profile of the needle is probably incorrect. Try filing a small square out of the very bottom of the slide with a needle file... I once read it somewhere I can no longer recall... maybe Gordon Jennings, but I dunno...
Way back when I was tuning yamaha's with mikuni carbs and expansion chambers.

...Driving the screwdriver into the 'pipes' inside the muffler to open them up just kinda changed everything! Time to re-tune... again! Make a change to the pipe, time to revisit the main jet. Then, the other settings.


IMO this thread shows, more than anything, that perseverance and going through the process step by step will get results in the end.
...and then as the engine gets broken in, U gonna have to go through it all over again ! LoL

Basically, these engines are SO SMALL, and we are expecting quite a lot from them. Things would be far simpler with a 5hp or better 4 cycle with flywheel mass to it. There's really no substitute for cubic inches!

..but that is a different game..

Best
rc
 
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longrider.scott

New Member
Nov 8, 2010
13
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California
I have just installed my first CNS carburetor and found it to not have any mid-range power. I really appreciate all the advice you guys have put out here. First I didn't use the plastic shim that came with the carb. It doesn't seal on the intake. Instead I used the CNC intake from Manic Mechanic. It's made to fit the carb very well. The one thing I noticed is the new intake doesn't allow the carb to be mounted level. Is this a problem?
I haven't tried to make any of the suggested modifications to the carb yet but will as soon as I can. Does anyone have any suggestions for replacing the stock air cleaner? Stock air cleaner seems to not breathe very well.
 
biknut

biknut

Well-Known Member
Sep 28, 2010
6,653
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Dallas
It seems like a lot of people totally don't understand the plastic shim. It has nothing to do will sealing the intake. All it does is make the carb fit the manifold. All the sealing is performed by the O-ring on the end of the manifold. It it leaks, you probably don't have the carb pushed onto the manifold far enough.

I didn't have any problems getting the carb to seal, and I didn't use any sealer.
 
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Sanction

New Member
Jun 1, 2011
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Central Florida
biknut said:
This is how I made the final adjustment,

There's a seam in roughly the center of the plastic float. I adjusted the float till the seam was parallel to the sealing surface of the float bowl.

Compared to stock, this made the fuel level slightly higher in the bowl.
Click to expand...
Is this adjustment with the needle depressed or just where the float touches the needle?
 
biknut

biknut

Well-Known Member
Sep 28, 2010
6,653
475
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Dallas
Sanction said:
Is this adjustment with the needle depressed or just where the float touches the needle?
Click to expand...
The needle is on it's seat, and the float is just resting it. These float needles don't have a spring in them like most float needles do. It's just a solid piece..
 
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PerryP180

New Member
Jun 24, 2011
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Atlanta, GA
I just removed the tube from breather to bowl. It's as if my engine has suddenly come alive. I can't thank you enough. I had already ordered a new NT Carb. to replace this on. I think I'll go ahead and get it just to be safe. Removing the tube from the bowl to breather has me smiling again.
 
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6cylturbo

New Member
May 22, 2011
18
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Indiana
ok so i pulled the hose on the outside of the carb that goes thru the back side of it and used duct tape to close it off and it runs great. left the other end of the hose connected to the nipple and with engine running held my finger over it and no difference that i could tell. no bogging like before and barely used choke at all. before i pulled the hose i had to work the choke to varying degrees throughout acceleration to top end. I thought i was going to have a helluva time tuning this thing but it's fine now.

can anyone tell me what that hose is/was doing? was it just put there to keep crap out of it during shipping? i read something about it awhile back but memory...
 
Greg58

Greg58

Well-Known Member
May 1, 2011
5,363
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Newnan,Georgia
That hose is the vent, do not cap it off either leave the hose open or use a small engine gas filter as I did. I have tried clsing it off and no fuel would flow into the carb. This is a EPA idea that doesn't work on some engines, they didn't want fumes venting to the air.
 
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rohmell

rohmell

Active Member
Jun 2, 2010
1,531
6
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New York
Greg58 said:
That hose is the vent, do not cap it off either leave the hose open or use a small engine gas filter as I did. I have tried clsing it off and no fuel would flow into the carb. This is a EPA idea that doesn't work on some engines, they didn't want fumes venting to the air.
Click to expand...
Pretty dumb to use a hose...They shoulda cast the vent into the carb like they did on the NT.
 
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6cylturbo

New Member
May 22, 2011
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Indiana
Thanks guys. Very much appreciated. Wanted to swap a different fuel filter from tank anyways. Guess I'll buy 2.

Amazing how well this thing runs now.
 
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6cylturbo

New Member
May 22, 2011
18
0
0
Indiana
Wow!! Shocking!! Yup, checking spark plugs. ran it and for a bit then pulled spark plug wire off spark plug since my kill switch doesn't kill anything. WOW!! Never thought I'd ever get spark all the way up to the family jewels. Thought I was on an episode of Jackass or something. Don't think I will ever do that again. Although I have a few friends I'd like to see if we can duplicate it with :)

Good news was that spark plug looks great!!
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
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San Diego, Kaliforgnia
I did that once on my Briggs powered mini bike. The little metal flipper to stop the engine on the cylinder head flew off, so I just yanked the spark plug wire off the spark plug.
Lit me up until the engine came to a stop. I could not let go of it, my muscles just tensed up. I went inside and laid down for a 1/2 hour to let the pain subside. After that I immediately re-installed the metal flipper.

Alternate ways to kill an HT engine:
At idle speed either let the clutch out while holding the rear brake on, or turn on the choke to drown the spark plug.
 
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6cylturbo

New Member
May 22, 2011
18
0
0
Indiana
i just picked up a weedwacker gas filter and a little bit of fuel line. should work quite well to protect from weather and still let it breathe. i figure a zip tie would keep everything in place too. i'll install in a bit but i need to stop sweating first. very humid today and i've been running around non-stop today.
 
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