Cheap Chinese bike

[SMOKEU]

I bought a mini motocross bike as a non runner, it seems to be in an almost brand new condition but it won't start. Spark is good and compression is good. When the fuel tap it turned on it leaks fuel from the carb overflow. Possibly a stuck float?

[Ray LeCheminant]

I bought a mini motocross bike as a non runner, it seems to be in an almost brand new condition but it won't start. Spark is good and compression is good. When the fuel tap it turned on it leaks fuel from the carb overflow. Possibly a stuck float?

Stuck float
Block chinese fuel filter
Needle and seat clogged

1. Take it off
2. Clean it will with carb clean or similar
3. Replace fuel filter with quality one

Fire it up.....

These carbs are famous for this.....
:2thumbsup

[SMOKEU]

I don't know what I'm doing when it comes to opening carbs up, I'll have a go at it though and if I can't fix it ill send it off to a lawnmower shop to have it looked at.

[CookMySock]

I don't know what I'm doing when it comes to opening carbs up, I'll have a go at it though and if I can't fix it ill send it off to a lawnmower shop to have it looked at.Take it to the track and get some help. If you are going to race these things then you are going to have to learn about them. You will see very quickly that once you have the lid off them, there is little or nothing in there that is difficult.

Before you do anything though, go up town and buy a new spark plug and close the gap up a bit. I bet it just goes.

Steve

[SMOKEU]

I took the bowl part off the bottom of the carby and there is this round plastic thing in the shape of a donut that just sits there. On top of that there is a half round metal thing but I have no idea what they should be doing. I can't get the carby off because the screws are at such an awkward angle a normal screwdriver can't get them off.

[imdying]

Right, that round plastic thing is the float. When the bowl fills up with fuel, it floats to the top, and pushes a wee needle valve into a seat, which stops fuel entering the bowl. When it uses a bit of fuel, the float goes down with the fuel level, and the needle comes out of the seat and lets more fuel through. And repeat again again again....

If that needle valve gets a little crap in it, it doesn't stop fuel coming through when the bowl is full (because the dirt is stopping the needle from sealing against the seat), and eventually fuel comes starts coming out the over flow.

So you need to ensure that the needle and seat are in good condition, and that there's no crap in them. Scare crap out of it with a can of carb clean.

You will need to take it off to clean it effectively, so figure out how to do that next. If you can't reach with your regular screwdriver, go buy one better suited to the job at hand.

[Ivan]

I am getting the same problem with my bike and searched forum and this is the closest i can get to my problem.

I have stripped my carb pulled it right down cleaned it up put it back together and it just leaked like crazy so I guessed the float heights were wrong so I have bent the tabs to allow less fuel which stopped the leak the engine ran but then sucked the bowl and died so I re opened the float height but now I can get my engine to run a spit of ether up it and she fires then dies so it definatly has a fuel issue I was just wondering if anyone on here has any suggestions?

What are the europeon carbs like? might buy one of those and make a manfiold to suit or something

[SS90]

I am getting the same problem with my bike and searched forum and this is the closest i can get to my problem.

I have stripped my carb pulled it right down cleaned it up put it back together and it just leaked like crazy so I guessed the float heights were wrong so I have bent the tabs to allow less fuel which stopped the leak the engine ran but then sucked the bowl and died so I re opened the float height but now I can get my engine to run a spit of ether up it and she fires then dies so it definatly has a fuel issue I was just wondering if anyone on here has any suggestions?

What are the europeon carbs like? might buy one of those and make a manfiold to suit or something

I have a bit of experience with a brand of carb called "koso", which are a copy of a Kiehn (in every way except part quality), and available over here in Europe, and purchased by the truck load by customers.

Generally, they work ok. The main problem is, like you say carb flooding.

The problem seems to be in the machining of the float needle seat. I first suspected (when faced with this problem) that the material of the needle rubber was too low quality, so, as they are the same as a Kiehn, I fitted an original needle.

No real change.

In this particular "Koso" carb, the float needle seat is pressed into the carb, and as such not replaceable, that's nothing new, Japanese carbs are quite often like that, but it does represent a dilemma.

95% of the time, I have to experiment with the float height in order to stop the flooding at idle (the height at which this is effective is always different, sadly)

If a customer has this carb (and many do) I have to "remedy" it like that, and advise them to ensure they switch the fuel off when not in use (even for a minute)

Occasionally (actually, quite often) they inform me that it will often flood when they are sitting at idle for too long.

BUT FOR SOME STRANGE REASON THEY WANT TO KEEP THE DAMN THINGS!

In all seriousness if you can obtain one, the good old basic Dellorto PHBH (available in 20mm 21mm 24mm 25mm 28mm 30mm 32mm 36mm and 42mm) is a great piece of kit (ok from the seventies) but they are cheap (and granted not "flat slide", just "round slide", but really easy to set up and parts are available)

You can easily switch them from 4 stroke setting to 2 stroke setting just by changing the emulsion tube (that's if you need to!)

Oooopps, rambling a bit, but in my experience, I have found the needle seat to be the problem.

If it is "pressed in to the carb" you may have to explore the idea of cutting a piece of round steel to the correct angle of the seat, and "re cut" the seat angle with some fine valve grinding paste....... I have had success with that before.

[newmanz]

I don't know what I'm doing when it comes to opening carbs up, I'll have a go at it though and if I can't fix it ill send it off to a lawnmower shop to have it looked at.

For less than $40 you can buy a complete new carb, honestly, many knock off bikes are sold with damaged carbs, factory defective carbs.. my advice, =

#1 undo carb from engine
#2 throw carb as far as you can over the neighbors fence
#3 buy a new carb
#4 bolt on new carb
#5 enjoy your bike instead of hours of fitting, taking off, undoing, getting pissed off.. with a carb that may never have run properly the first day