66cc China Girl Motor runs too rich at low throttle, can't adjust anymore!

[JohnnyCrash]

Hi eh!

Just got my China Girl ticking, it uses the stock exhaust and NTTC (NT?) carburetor with stock air cleaner, the square black plastic one. I'm using the stock 10-tooth engine output sprocket and 44 tooth rear sprocket.

Initially, it ran extremely rich. It wouldn't even fire at all with the choke on, when I took it off it fired right up. It four-stroked badly at all throttle settings and bucked like crazy at low speeds.

I started by taking the 0.028" stock jet and soldering it up, then drilled it with a 0.022" drill, which ended up giving about a 0.024" hole. The full-throttle running is now excellent and top speed is thoroughly nuts for a 44T rear sprocket, probably around 55 km/h (35 MPH) or so

Problem is, at low speeds and small throttle openings, it still four-strokes like crazy. I adjusted the jet needle to the leanest setting (C-clip at the top end of the needle) but it doesn't seem to have helped. At low speeds the engine runs rough, bucking like a bull and trying to run the bike at normal pedaling speeds results in four-stroking as the bike accelerates to a steady-state speed at around 1/4 throttle or less. The four-stroking only stops if I apply more throttle, but of course I end up taking off eh! Fuel consumption is, of course, higher than it should be at low power settings. At about half-throttle or more it runs great and the spark plug comes out at the ideal light-brown colour.

I want to be able to run the bike across a wide speed range, but can't use the small throttle opening range. I'm all out of adjustments! I'm currently using Castrol Super 2-Stroke oil at 20:1 ratio. Running less oil will only enrich the mixture, making the problem worse.

Any ideas? I'm surprised that adjusting the C-clip on the jet needle across all of the grooves seems to have almost no effect (I'm currently running it on the leanest setting, to no avail). Has anyone ever modified an NT carb to incorporate an air bleed?

Thanx!

Ian

 

[shwnrttr]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

mine had a similar issue, i ended up having to bend the tabs on the float so it would sit lower in the bowl. try that, u might have to play with needle clip setting after that. good luck

 

[dan428]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

mine had a similar issue, i ended up having to bend the tabs on the float so it would sit lower in the bowl. try that, u might have to play with needle clip setting after that. good luck

my new engine also '4-strokes' at all speeds and I'm trying to figure out how to fix it. what is the float? is it in the carb, and how do you adjust it? just unscrew the 'bowl' from the carb assembly? does it regulate the gas/air mixture?

 

[JohnnyCrash]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

dan428, the needle that fits into the throttle slide controls the mixture at up to about 2/3 throttle, above that the main jet controls the mixture. Tune the carb for best full throttle running first by replacing the main jet, since you're 4-stroking use a smaller jet.

Get that right, then adjust the clip on the needle to give best running below 2/3 throttle.

Finally, for best running at idle and small throttle openings/low speeds, you would adjust the idle air bleed, which unfortunately these little carbs don't have!! Maybe I'll try retrofitting one.

Ian

 

[JohnnyCrash]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

mine had a similar issue, i ended up having to bend the tabs on the float so it would sit lower in the bowl. try that, u might have to play with needle clip setting after that. good luck

I did that, but it had no effect. The needle is already at the leanest setting and adjusting the float height has no effect (strangely enough). Engine runs well at half- to full throttle, but tends to 4-stroke below that, it's especially bad at low speeds.

That's how these engines thank you for fixing all the intake leaks

 

[fonzie]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Just for a test, remove the air filter and see if the unit acts like it is lean at WOT. You will know immediately. Do not run it lean for any length of time. Might help your low end .....then rework your C-clip, and main jet to compensate. Find out what works. If the unit runs better then put about a 1" hole in the air cleaner housing and put it back on. These engines are all different and what works on one might not work on another. You need to try it and see if that works.

 

[JohnnyCrash]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Just for a test, remove the air filter and see if the unit acts like it is lean at WOT. You will know immediately. Do not run it lean for any length of time. Might help your low end .....then rework your C-clip, and main jet to compensate. Find out what works. If the unit runs better then put about a 1" hole in the air cleaner housing and put it back on. These engines are all different and what works on one might not work on another. You need to try it and see if that works.

Hi Fonzie (EEEEEHHHHHH! *thumb up*)

Thanks for the tip, this did cross my mind, but I'm not too keen on running without an air filter for any amount of time!

I figure since the engine runs well at larger throttle openings and the bike goes so damn fast ('till my butt cheeks are liquefying from the vibration!), the air filter is fine, as a restrictive air filter would cause the most problems at high speeds. It's very low speeds/small throttle openings that cause the bike to 'buck' like crazy at idle with the clutch out and it also four-strokes a lot at small throttle openings when the bike reaches steady-state speed.

Perhaps I'm just pickier than many other folks and they don't notice it, or don't care much if they do notice, but I think this engine could run better when going slowly and get much better low-speed fuel economy than it already does.

Peace

Ian

 

[dodge dude94]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Get an sbp filter. Looks boss and has increased airflow that can help with your rich condition.

 

[JohnnyCrash]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Get an sbp filter. Looks boss and has increased airflow that can help with your rich condition.

...except the stock air filter allows me to go like snot, I haven't measured it but it's over 50 km/h, because I can easily keep up with cars in 50 zones, so it isn't air filter restriction that's causing it. The 4-stroking and bucking happens at very low speeds and at anything less than a little under half throttle.

I'm contemplating putting an air bleed on the carb. The stock manifold didn't fit the carb (NTTC unit) properly, I have 2 carbs and 2 manifolds and neither set ever fit right, allowing 4 small air leaks at the carb-to-manifold joint.

When fitted with the original jet, these air leaks probably allowed the engine to run properly at part throttle! Now that all air leaks have been fixed (by machining the manifold to fit the carb properly) there needs to be an air bleed from the inlet to the outlet side of the carb, allowing filtered air in after the throttle at high manifold vacuum, instead of unfiltered air getting in through the 'stock' air leaks.

Peace

Ian

 

[LaLongueCarabine]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

"I figure since the engine runs well at larger throttle openings and the bike goes so damn fast ('till my butt cheeks are liquefying from the vibration!), the air filter is fine, as a restrictive air filter would cause the most problems at high speeds. It's very low speeds/small throttle openings that cause the bike to 'buck' like crazy at idle with the clutch out and it also four-strokes a lot at small throttle openings when the bike reaches steady-state speed."

Not necessarily, I had the same symptoms as you but went the wrong way with my jets and kept installing bigger ones. When I put a free flow air-cleaner (and the stock jet back) I have great low and medium power. (my belief is that you're not getting air at slow speed, too much fuel but not enough air. I know it sounds wrong but it did work on all 3 of our bikes.)

Your jet size seems perfect to me,perhaps one size smaller?

Wish I was more help.

I finally added a expansion chamber and a 36T rear sprocket and my bike is very happy now. I beat everyone off the line but my bros are higher geared so their top is 4-5
mph faster. I get 29-31 mph (46-50 kph) with top speed down hill at 37 mph (59 kph)

 

[nightcruiser]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

I don't run the NT carb, but hearing you say it's rich at idle and consuming way too much fuel makes me want to second the suggestion you need to do a float adjustment. I know you said you did that already, but maybe not enough, or the wrong way? Or maybe your float has a leak? Does it take on any fuel in the floats? When a float takes on fuel it can cause this sort of problem... Or maybe the needle valve is letting some fuel sneak through when it is supposed to be closed for some reason? (Dirty or a metal burr somewhere?) Just seems like a float issue to me...
Or maybe the wrong needle somehow got in your carb? Might try another needle....

 

[nightcruiser]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

my new engine also '4-strokes' at all speeds and I'm trying to figure out how to fix it. what is the float? is it in the carb, and how do you adjust it? just unscrew the 'bowl' from the carb assembly? does it regulate the gas/air mixture?

Dan,
It's best not to jump into someone else's thread looking for help, it may seem like you have the same problem but we don't even know if you have the same motor/carb? Depending on what you're running advice may be different.

To answer your question in a generic fashion, yes, the float is in the carb and it is a device that turns on and off the fuel flow into the carb bowl by closing the needle valve to maintain a certain amount of fuel in the bowl. An improper float adjustment can make a motor run very rich or even cause fuel to overflow from the carb.

If you want to fix your 4-stroke situation I would suggest you figure out what motor and carb you have, then first search the forum for threads about tuning that carb, most likely it's been covered here many times before. Or you can create your own thread asking for help, start out by telling what motor and carb you have, and what your symptoms are, you will get good advice. Trying to troubleshoot two different situations in one thread can be confusing...

 

[nightcruiser]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

PS On the float...
You can do an easy test to see if the float may be causing your issue. After the bike is warmed up and exhibiting the bad behavior turn off the valve on the fuel tank. This will cause the fuel level in the bowl to drop no matter what the float is doing. If the bad behavior goes away briefly before she runs out of gas you probably have a float issue....

 

[JohnnyCrash]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Thanks for everyone for helping me out with this, yes the engine was running far too rich at small throttle openings, but ran perfectly at half or more throttle. I'd have used an adjustable air bleed to offset the rich mixture at part throttle if I were to continue with this project, it's a really nice engine and ran beautifully.

The cops nailed my nuts to the cross a couple days ago, seven court summons for 'improperly equipped motorcycle' and a pile of paperwork issues. They're rabid about it here, it seems. Looks like I'm in *seriously* deep dung on this one, we must live in such a wonderfully flawless world for the judicial system to get so bent out of shape over a grown adult tinkering with his bicycle... It's great to know the nice officers are hard at work keeping our world perfect and ridding society of antisocial menaces like myself.

Had a great time rebuilding my engine and getting it to run nicely, but it looks like I won't be going any further on it...

Thanks for the fun three days China Girl, time to look for some action on someone else's street corner

D*mn cops

Ian

 

[LaLongueCarabine]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Wow, that really sucks! The Cops here ignore us completely, as long as we wear bike helmets. Last week we all three of us blew through a stop sign and the cop didn't even look at us.

Did find out though that we should have motorbike driving license here.

 

[Kcip]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Hey JohnnyCrash, how did you make out with your summons issues?

 

[JohnnyCrash]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

Hey JohnnyCrash, how did you make out with your summons issues?

It'll take a while, but the crown attorney just chiseled it down to one charge, driving with improper license.

I haven't used the bike since I got busted.

I have yet to go to court in November; hopefully, the judge will let it slide since the police destroyed my car when an officer ran a red light and clobbered me--my reason for building the bike. I wonder if the cop got a slap on the wrist or anything for destroying private and public property--because I certainly got a kick in the nutz for trying to find an alternative to the now-deceased car. Rust in , Corolla...

Ah, government... Parasites.

Ian

 

[borntofli]

Re: 66cc China Girl runs too rich at low throttle, can't adjust anymore!

I have-had 2 bikes w/ this same problem.... I lowered the float on both and it only helped 1....Now this bike runs smooth from idle to wot....

The other one not sure what the problem is... Will have to keep messing w/ it...