Why does my bike not go up hills ? grubee gt2b 48cc , cns carb

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greggasbike

New Member
Nov 23, 2010
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north carolina
Yes, I did the search function and found way too many threads to go through and not sure even if they were the same issues... so I will post this to see if people who have the same kit / carb have had this issue and how it was resolved.

The bike starts fine , gets up to temp fine , and rides fine at full throttle.

BUT , you go up even the slightest hill and the engine dies out.....
Are these bikes even able to go up hills on there own power ?

If I try to get up speed before a big hill , it still doesn't work, once I hit the slope .... its peddle time....

What adjustment is needed ???? can you even adjust the float ? ( thats what a local scooter mech said )

thanks for your help ! keep em riding !
 

adam valentine

New Member
Sep 27, 2010
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Mission Kansas
yes they can climb hills but they are only a few hp different factors can change there ability such as your weight sprocket size intake and exhaust float is not problem unless your starving for fuel try a bigger sprocket
 

LS614

Active Member
Dec 22, 2009
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Here's my own thoughts on this. I had a scooter with a cruddy engine once, it was 24cc, and only rode downhill even though it revved fine. It would only carry me up a hill when it was on 3/4 choke. Here's what I think, I think your engine is starved for fuel. There are several things that could be causing this. 1) Very likely, there is some kind of air leak behind the carb that is messing up your mixture. 2) you have dirt stuck in a jet that is allowing some fuel to pass but not enough or 3) your float bowl is somehow sticking in the up position. Hope this helps. A way you can test to see if it is fuel starvation is to get it running and then play with getting it to idle with as much choke on as possible without touching the idle screw at all. If you can get up a hill with almost full choke, you probably have one of the three things wrong. Hope this helps
-LS
 

give me vtec

New Member
Jun 19, 2009
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SoCal
it's probably your carb... the cns carbs are plagued with problems from the get-go. these engines definitly have enough power to get up a hill. even if it didn't.... it shouldn't die on you.

my recommendation is to buy an older nt carb...
 

greggasbike

New Member
Nov 23, 2010
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north carolina
yeah , I think I am done w/ these CNS carbs..... performance carb ?? what performance ?

There are no airleaks , its getting fuel .... I have two MB's and its doing the same on both .... I wish Grubee had customer service ... really ... they are made in China , we outsource everything in America... why can't they just outsource customer service too,.... then at least we would have something....

I looked at the one thread w/ the exploded view of the CNS carb .... are you kidding me .... my 1969 vw carb is simpler than this.... and easily adjustable...

Looks like I am purchasing the cheap older carb .... wish I bought the crappy boygofast kit .... doesn't seem like those people have any probs w/ carb and what not ....lol
 

greggasbike

New Member
Nov 23, 2010
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north carolina
I am guessing the name of the "cheaper" ( but actually functions correctly carb) is called the NT ?

If anyone wants to trade carbs , I would be willing to even trade my CNS carb for the cheaper one... then I would have one of each and can get a true look at the difference and see which one really is better...

It just bothers me... all I want to do is ride this bike and problem after problem...

Gas prices just hit $3.75 in my area ..... stooped carbs .....
 

LS614

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Dec 22, 2009
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greggasbike

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Nov 23, 2010
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north carolina
Its not broken .... its just not possible to actually adjust these things correctly... not really into spending 10-20 hours on a carb adjustment when I can buy one that is plug and basic play...

I am sure it can be fine tuned... but its not a race bike ... I just want to basically ride it...

It took me two days to rebuild an entire 1600cc vw engine , carb took 2hrs , put the engine back in ... and 7,000 miles later .... ZERO problems.... guess they knew how to build things then..... especially build things that people could easily fix..... ( fast forward to USA and GM , they purposely built cars in the 1980's that you had to take to a shop , lol ..... 20 yrs later ... they are bankrupt and can't make a decent car ...lol )
 

LS614

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Dec 22, 2009
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Lol, yeah, sorry if it seemed like I was bashing you, it's just it sounds like it has given you a lot of trouble. I'll ask around and see if I can hook you up with an NT for cheap :)
 

greggasbike

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Nov 23, 2010
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north carolina
I am going to purchase the one you sent in the link .....

These days I have so much stress in my life w/ job shee , the economy , and everything else ....

This bike is something for enjoyment and to save money.... currently its doing neither !!!
 

LS614

Active Member
Dec 22, 2009
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sorry it's not a joy RIGHT NOW, once the bugs are worked out, you'll love it for sure! Then you can give it a name :)
Peace -LS
 

superbob

New Member
Mar 7, 2011
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Florida
Its not broken .... its just not possible to actually adjust these things correctly... not really into spending 10-20 hours on a carb adjustment when I can buy one that is plug and basic play...

I am sure it can be fine tuned... but its not a race bike ... I just want to basically ride it...

It took me two days to rebuild an entire 1600cc vw engine , carb took 2hrs , put the engine back in ... and 7,000 miles later .... ZERO problems.... guess they knew how to build things then..... especially build things that people could easily fix..... ( fast forward to USA and GM , they purposely built cars in the 1980's that you had to take to a shop , lol ..... 20 yrs later ... they are bankrupt and can't make a decent car ...lol )
Same problem with the same carb on the same engine, bro. But after reading what was out there I wanted to find out about both carbs for myself so I ordered an NT and set to work on the CNS - stands for central nervous system, by the way.

I too am from the old VW school, and this CNS acts weirder than any funky, ancient, used-up carb full of resin and rust that I ever ran across, and that's saying a lot since this is brand new gear. Usually at some point deliberate, calculated, organized experimentation produces sense out of funk. Once you've come out on top of it with an antique carb, with it's own weird physics going on and its own unique set, you never forget, you have sort of learned how to patiently learn.

That said, after block-sanding the intake tube and sealing up the carb-intake connection with RTV silicone; checking that the intake gasket is perfect; sealing other necessary gaskets with RTV; completely redoing all the wiring just to be sure; torquing the head; adjusting the float, the idle, the air/fuel and the needle through their complete ranges, out away from recommended settings and back again; employing every single tuning method that was posted and some that weren't; after all that and sacrificing a chicken, the best I've been able to do is to get a pretty strong, smooth mid- and hi-range, good strong hill climbing except for when it just doesn't want to do it at all (?!), good starting except for when it dies at a stop and then it starts very hard; and a low, steady idle. Except for when it just doesn't idle, but dies, which happens about 10% of the time I pull in the clutch. About 75% of the time it will climb a hill without coaxing the throttle and without any hint of bogging. Oh, and I can never let off the choke all the way or the engine will rev fit to fly apart. My choke plunger lives about 1/4in above its rest, cold or warm.

And I'm at my limit. That's the best I can do and that's all I care to do, until the NT carb comes, and then when I bolt it on and just go, I won't feel silly at all about posting a picture of my well-hammered CNS and talking trash about it.
 

justcruising

New Member
Mar 9, 2011
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ontario canada
check your float, i had somewhat of the same issue, and when i took it apart the float was filled with gasoline. I dont know how it got in, i was trying to find the hole in the float but to no avail. Sure fixed my issue though :)
 

ferball

New Member
Apr 8, 2010
598
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NH
Check the fuel tanks, debris gumming up the line is not unheard of on these engineering marvels.

Having never played with a CNS carb, are they similiar to a chainsaw carb? No floats just a diaphragm and such?
 

superbob

New Member
Mar 7, 2011
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Florida
check your float, i had somewhat of the same issue, and when i took it apart the float was filled with gasoline. I dont know how it got in, i was trying to find the hole in the float but to no avail. Sure fixed my issue though :)
Brand new float, but I checked it anyway, and experimented with bending the tab to adjust the float level. But when my NT carb came... just bolted it on, and all the problems went away. Had it dialed in within two miles. Fixed. Until a new set of unrelated problems surfaced.

Is that the way with these engines? A new problem every day, until you're an expert? Brand new gear that acts like antique gear?
 

superbob

New Member
Mar 7, 2011
17
0
0
Florida
Check the fuel tanks, debris gumming up the line is not unheard of on these engineering marvels.

Having never played with a CNS carb, are they similiar to a chainsaw carb? No floats just a diaphragm and such?
No. The CNS carb has a plastic float much like that an an old VW, with a hinge and a needle and an adjustment tab. In fact, it reminds me of the old Solex on the 60-horse VW engines: pretty complex for the purpose. I wonder if Grubbee didn't simply get a deal on the CNS and leave it to us to try to adapt them to our engines. Once I tried the NT I realized how mismatched the CNS probably was to my 48cc Skyhawk.
 

ferball

New Member
Apr 8, 2010
598
2
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NH
I got rid of my Solex for the after market Webber. I got sick of trying to dial it in. Sounds like the CNS is in the same boat.