New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 15, 2013 13:45:28 GMT -5
So im gonna jump right in to it. I am trying to replace my stock main jet. I purchased the complete set of replacement jets from ebay that run from 100 - 140 in size. www.ebay.com/itm/150cc-GY6-CVK-MAIN-JET-SET-FOR-CHINESE-SCOOTERS-ATVS-AND-KARTS-10-PC-SET-/161055682293?pt=Other_Vehicle_Parts&hash=item257faaaef5&vxp=mtr I'm having a problem determining the appropriate size for my scooter due to the fact that my stock jet does not have a marking of its size. I have tried a couple of different sizes but all tend to make my scooter run differently and not efficiently whether it be loss of speed or loss of idle. So far I understand that the size of the jet is determined by a number of different variables, for example the size and style of air filter. and other things that i just don't know about. So my first question is what is the best way to determine the appropriate main jet size for your scooter? I also would like to have a better understanding of how the carburetor works. I know that adjustments can be made to the carb by use of the Idle Speed Adjustment Screw:  and the Low Speed Mixture adjustment screw:  Which brings me my second question, what are the direct effects that these screws have on the carburetor? Scooter Thanks! |
|
Sophomore Rider
Currently Offline
Posts: 239
Likes: 1
Joined: Mar 13, 2013 9:13:17 GMT -5
|
Post by jeffery5568 on Aug 15, 2013 13:52:03 GMT -5
The only screws that really have an effect would be the idle screw which adjust the idle speed and the mixture screw which adjust the air fuel mixture its good for very fine tuning mostly at idle.
|
|
Sophomore Rider
Currently Offline
Posts: 239
Likes: 1
Joined: Mar 13, 2013 9:13:17 GMT -5
|
Post by jeffery5568 on Aug 15, 2013 13:53:53 GMT -5
As far as jets it depends on other mods you have done like air filter and exhaust. Scooters run lean from the factory so if yours is stock I would put a 110 in it and that should do well.
|
|
|
|
Post by scootnwinn on Aug 15, 2013 13:58:15 GMT -5
Wow? Why are you rejetting? You don't always need to. When you do you will definitely need to adjust the idle, fuel mix screw, and possibly the needle height. If the bike is running ok why would you open this can of worms. If it isn't we can help better if you described the issue your having. You don't necessarily need to rejet a stock bike...
|
|
New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 15, 2013 14:21:41 GMT -5
The only screws that really have an effect would be the idle screw which adjust the idle speed and the mixture screw which adjust the air fuel mixture its good for very fine tuning mostly at idle. Thank you for your response. What are the details to these screws. What do they do exactly for example blocking and opening to what or from what and what is it blocking be it air of gas. |
|
New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 15, 2013 14:23:04 GMT -5
As far as jets it depends on other mods you have done like air filter and exhaust. Scooters run lean from the factory so if yours is stock I would put a 110 in it and that should do well. Appreciate the response, i will try that size out and see how it does. As far as mods i have replaced the air filter to a smaller high performance filter. |
|
New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 15, 2013 14:24:51 GMT -5
Wow? Why are you rejetting? You don't always need to. When you do you will definitely need to adjust the idle, fuel mix screw, and possibly the needle height. If the bike is running ok why would you open this can of worms. If it isn't we can help better if you described the issue your having. You don't necessarily need to rejet a stock bike... Thank you for your warning, but i am doing this for the knowledge when I work on something I have to take it apart to understand how it works. This is my hobby so i like to dig deep... ;D |
|
|
|
Post by scootnwinn on Aug 15, 2013 14:27:16 GMT -5
Taking it a part is good but randomly changing jets for no reason can seize your engine...
|
|
|
|
Post by pmatulew on Aug 15, 2013 17:47:48 GMT -5
The idle speed screw is just a lower limit stop that holds the butterfly inlet valve open a little bit to maintain a given idle speed. At anything above idle it doesn't do anything.
The idle mixture screw depending on the manufacturer and the placement is either and air adjust or a fuel adjust. Either way you are fine tuning the low speed mixture. I believe that when the screw is on the downstream side it is a fuel adjust. Counterclockwise/richer. Clockwise/leaner.
At least you're asking first. I have a bad habit of taking things apart and then asking questions.
|
|
|
|
Post by ltdhpp on Aug 15, 2013 18:10:37 GMT -5
how does it run right now? have you done plug checks?
It's possible the one you have in it is fine. An air filter alone isn't a huge change anyway if your kept the stock exhaust. Mine ran good with just a filter with what I estimated was a 108 jet, which was in my carb when i got it. I say estimate because I don't have a pin gauge, but the next best thing is a torch tip cleaner set. With those you can at least compare what you've got with the other sizes that are identified by the kit.
Another significant adjustment is your main jet needle height. You can take of the carb's top cover and pull the spring and diaphragm/slide piece out. In the slide you will find the needle held into the slide usually with a small screw and plate. Remove this and the needle comes out, which will usually have several notches and a clip you can move around to change the height. Experiment with this first, and if it runs best at one extreme, then change jet size one step and repeat.
|
|
New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 16, 2013 10:42:02 GMT -5
The idle speed screw is just a lower limit stop that holds the butterfly inlet valve open a little bit to maintain a given idle speed. At anything above idle it doesn't do anything. The idle mixture screw depending on the manufacturer and the placement is either and air adjust or a fuel adjust. Either way you are fine tuning the low speed mixture. I believe that when the screw is on the downstream side it is a fuel adjust. Counterclockwise/richer. Clockwise/leaner. At least you're asking first. I have a bad habit of taking things apart and then asking questions. Thanks pmatulew, that's exactly what i was looking for. The idle speed mixture makes sense cause I can see it move when i adjust the screw. The low speed mixture on the other hand is where I start guessing. Counterclockwise/richer Clockwise/leaner does help me understand it better, i just don't know if it is gas or air. I do know my carb looks exactly like the one in the picture i posted and the mixture screw is in the same place. |
|
New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 16, 2013 10:53:56 GMT -5
how does it run right now? have you done plug checks? It's possible the one you have in it is fine. An air filter alone isn't a huge change anyway if your kept the stock exhaust. Mine ran good with just a filter with what I estimated was a 108 jet, which was in my carb when i got it. I say estimate because I don't have a pin gauge, but the next best thing is a torch tip cleaner set. With those you can at least compare what you've got with the other sizes that are identified by the kit. Another significant adjustment is your main jet needle height. You can take of the carb's top cover and pull the spring and diaphragm/slide piece out. In the slide you will find the needle held into the slide usually with a small screw and plate. Remove this and the needle comes out, which will usually have several notches and a clip you can move around to change the height. Experiment with this first, and if it runs best at one extreme, then change jet size one step and repeat. Thank you for your descriptive response, I will try this. Right now my scooter is running richer or so it seems to me. My ways of deducting are mostly made up, but it runs fine when Im driving but at idle sounds like it is flooding, the engine will slow down until it shuts off. I have also noticed that the exhaust is hotter then usual. so by adjusting the needle height am I controlling the gas flow or flow of air or is it both? Thanks again for your help, I like understanding how things work not just knowing how to fix a problem and you are helping me to achieve that.  |
|
|
|
Post by ltdhpp on Aug 16, 2013 11:00:39 GMT -5
The fuel/air screw on carb like ours opens/closes the idle fuel circuit so if you turn it counter clockwise it will let more fuel though (I think) and may cure your idle issue. the 'norm' on that is about 2 1/2 turns out from all the way in.
Adjusting the needle lets more or less fuel through the main jet, depending which way you go. Think of the needle as a tapered plug for the main jet. At idle, the slide is all the way down, so the needle plugs the jet. As you rev up, the slide lifts the needle to let the fuel flow you need to accelerate. The taper of the needle is why changing it's height changes flow - the more needle that's in the jet (the lower it is) the less fuel it lets out.
|
|
New Rider
Currently Offline
Posts: 15
Likes: 0
Joined: Mar 11, 2013 18:27:34 GMT -5
|
Post by derek on Aug 16, 2013 12:00:38 GMT -5
The fuel/air screw on carb like ours opens/closes the idle fuel circuit so if you turn it counter clockwise it will let more fuel though (I think) and may cure your idle issue. the 'norm' on that is about 2 1/2 turns out from all the way in. Adjusting the needle lets more or less fuel through the main jet, depending which way you go. Think of the needle as a tapered plug for the main jet. At idle, the slide is all the way down, so the needle plugs the jet. As you rev up, the slide lifts the needle to let the fuel flow you need to accelerate. The taper of the needle is why changing it's height changes flow - the more needle that's in the jet (the lower it is) the less fuel it lets out. Perfect! That makes alot of sense, i'm gonna take a look at it today and ill post what I find. Thanks again  |
|
