New China girl carb problem..help!

nomad69

New Member
Feb 18, 2017
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midwest
This is my second 2 stroke 5o cc china engine, mounted it on a mountain bike. I got it running, but then came the carb problems. It started to leak gas through the carb filter all over the bike. Took carb apart to see if anything was out of place. Put back on and the problem kinda went away. The engine starts but throttle grip wont move. I can throttle up the bike using the choke lever.. WTH!! I played with the "C" clip.. moved it up one notch, tried one down from factory.. nope still having the problem, then moved it back to factory setting. I have had the gas blow out the head gasket and muffler.

Basically I start the bike with the choke level in the upward position, but when I go to lower the choke lever the bike engine speeds up, and if I put the choke lever all the way down it cuts out. The choke lever is acting like the throttle.. WTH

Should I get/replace carb with new one or upgraded one, this carb seems to be cheaply made.

I've had nothing but problems with this engine, including the shipping woes.. I'd thought I try to fix this carb problem first and see if this kit is worth keeping. I've read that these china girls always need tweaking. I don't want to tweak .... I want an engine that's suppose to work
. I got better things to do than to "F" with an engine/carb all the time.

I don't want to buy a 500 engine, but I also don't want pos. A nice simple engine than runs constantly with out much maintenance. Any suggestions on this?

P.S. Do I need to turn off the petcock when I turn off the engine?
 
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crassius

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Sep 30, 2012
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there is little to go wrong with these NT-style carbs - I'd guess you put the slide in backwards or upside down
 
Jan 21, 2015
610
21
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Portland, Oregon
Try lowering the float level to fix the fuel leak. Also check if there is any dirt or anything stuck to the float or in the bowl. When I used to have a 2 stroke, my carb leaked once, turns out a grain of sand was stuck to the float and it made it not actually float and instead get stuck.
 

nomad69

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Feb 18, 2017
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midwest
I can get it to start and idle, but the throttle on the handle bars won't twist. Like I said it starts and idles ok. It idles ok when the choke lever is in the upward position, and as soon as I push the choke lever down, it speeds up and the farther it goes down position it starts to cut off completely.
 

Tyler6357

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Mar 15, 2012
1,143
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Santa Barbara, CA
I have had the gas blow out the head gasket and muffler.
If gas is blowing out the head gasket you have an air leak at the head gasket. Replace the head gasket, make sure the head sits flat and there are no air leaks. if it doesn't sit flat you can sand the cylinder using something flat like a piece of glass.
 

nomad69

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Feb 18, 2017
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midwest
It's a brand new engine. I think I left the petcock on and it flooded engine and when I went to crank it on all that gas came flying out the head gasket and muffler. I did torque the head down a little more. That's not my problem.

I start it up and it idles when choke lever is in the up position but when I start to lower the choke lever down it quickly speeds up and quickly stops running with the choke level all the way down position.

The handle bar throttle is stiff to move or doesn't at all while idling. Some where it needs adjusting...the sleeve in the carb isn't sliding up or down? cables? IDK?....grrr

I could run the bike at full speed just using the choke lever..one hand on the choke lever and left hand on bike grip...going 30 mph...what could go wrong?....lmao.duh.

P.S. How man turns in/out for the Idle screw?
 
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Chaz

Well-Known Member
Jun 3, 2012
1,004
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Vancouver, British Columbia
Like crassius said, make sure your carb slide is working properly. Easy enough to have the slide in backwards when you re-assembled the carb.

That may be your throttle stiffness problem. Also check your cable routing for pinch points that bind the inner cable.

Check for air leak at the carb intake. This may be causing your choke/throttle problem.
 

Tyler6357

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Mar 15, 2012
1,143
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Santa Barbara, CA
When you start it up (with the choke on) can you feel any air shooting out anywhere around where the head and the the head gasket connect? If so, you have an air leak, make sure the head nuts are torqued down to about 15 foot pounds.
 

Agreen

Member
Feb 10, 2013
792
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Southeastern GA
It sounds to me as if when you reassembled the carb, you somehow got the slide stuck. Possibly stuck wide open. With the choke on it can idle, but as you start coming off the choke you're making it more lean... closer to a good stoichiometric mixture... thus the higher revving. There is a really small notch on one side of the slide. That's for the idle adjustment screw to adjust how far the slide can come down. On the opposite side there's a cut all the way down the slide. That's for the tiny little locator pin in the cylinder of the carb to keep it from moving. If I had to guess, you probably need to rotate the slide 180 degrees. The notch is probably sitting on the locator pin.
 

nomad69

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Feb 18, 2017
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midwest
I'll pull the carb off again and double check...again.. lol. I'll get back to you guys again, maybe tomorrow.

Whats the idle screw set/turns in/out.

Thanks for the help. This carb ain't gonna get the best of me!
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
There's not a set number of turns for all carbs. It's just whatever makes it idle. Once I get it running, I keep it up with the throttle and keep cranking in on the idle screw until it holds an idle by itself.

(Edit: I found a video)
https://youtu.be/mpP0i-VXuzg
 
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nomad69

New Member
Feb 18, 2017
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midwest
Well, I got the throttle working. Took the sleeve out and made sure it was in the right position and adjusted the throttle cables. But the rear tire had a flat, fixed that, then went to start it and the chain snapped.. WTF ...and I don't have another one at the moment.
So when I get a new chain, I'll test the engine again.. till then I'll get back to you guys.

Thanks for all your help guys.
 

Tyler6357

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Mar 15, 2012
1,143
170
63
Santa Barbara, CA
The chain should have some slack in it on the part that feeds into the engine sprocket from the rear sprocket, don't put the chain on too tight! If it's too tight it will sometimes jump the rear sprocket be become wedged between the spokes and the sprocket. Move the chain tensioner forward or back on the frame until you find the right spot. Lock the clutch lever and get the back wheel off the ground while you peddle it with your hand so you can make certain the chain is flowing smoothly before you get on and try to start it.
 

nomad69

New Member
Feb 18, 2017
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midwest
Tyler, When I had to replace rear tire tube, the tire did not go back exactly where it did prior. So I did tighten the tensioner but not extreme, I know better than that, it had 1/2 inch play.
The problem that was lurking for awhile. Originally I cut the chain at the wrong link and had to rig it up so I could at least get the bike up and running.

That's why I started the other thread "What size chain"... I is out of chain...
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,143
170
63
Santa Barbara, CA
Tyler, When I had to replace rear tire tube, the tire did not go back exactly where it did prior. So I did tighten the tensioner but not extreme, I know better than that, it had 1/2 inch play.
The problem that was lurking for awhile. Originally I cut the chain at the wrong link and had to rig it up so I could at least get the bike up and running.

That's why I started the other thread "What size chain"... I is out of chain...
I understand, you can never get the rear sprocket perfectly lined up with the engine sprocket and get the rear sprocket so that it spins with no wobble, so it's important to have some slack in the chain so it can handle the wobble. I'm using a very strong BMX chain. It's thinner than the bulky 415 and clears my tire better and also goes through my engine sprocket with less drag. I am using a sprocket adapter on my rear wheel and not the stock rag joint set up and I still can't get it to spin without a slight wobble.
 

nomad69

New Member
Feb 18, 2017
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midwest
Ok, got the new chain installed correctly . I then got the carb sleeve to slide up and down while moving the throttle.

Something is still off with the fuel/air mixture imo.

I can get the engine to idle "barely" with choke lever in the up position, but the second I start to slide the choke lever to the down position it CUTS OUT.

When the choke lever is in the up position and engine is idling, I go to use the throttle, the engine doesn't speed up or slow down...it doesn't do anything!? The sleeve is moving but the engine just sits there and idles with the choke lever in the up position.

I tightened the head gasket down, I wrapped tape over the pipe where the carb slides onto, for possible "air leak" Everything seems snug!

I have no idea whats going on! Grrrrr...
 
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crassius

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Sep 30, 2012
4,032
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USA
sounds like a simple problem - if someone near you works on these, he would most likely see what's wrong right away

relax a bit, then try going thru carb internals and float level and fuel flow thru lines and carb seating on intake without thinking "I already checked that & it is good"