Post by motomech on Feb 27, 2008 2:55:35 GMT -5
the forum has moved
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These basic methods apply to carb cleaning, but also have relevance in trouble-shooting defective "made in China" carb.s(defective new Japanese carbs are unheard of).
The area we will focus on is the idle or low-speed circuit, but I will briefly touch on a couple things first.
Most of these scooters are still too new, but carb.s in which gas has sat. for a period of time, can become quite a smelly, green mess. The worst of them had their condition worsened by a leaky petcock or vac. gas valve that would allow the bowl to keep re-filling while the fuel was evaporating away. Cleaning all the parts can get quite laborious and in the end, one usually just scrapes away most of the residue with a sm. flat screwdriver and sm. wire(brass) brush.
It seems like everyone one has their favorite carb cleaner, but in most cases, any carb spray can will work. Really nasty units will need to be soaked and in a sm. %, need to be taken to the shop to be soaked and agitated. How to know? Well that's what we are getting to, but first;
Float levels- Some of the floats on these scooters are plastic, non-adjustable and rarely leak. What is a concern, is the ability of the float needle to stop the flow into the bowl. Simply connect a aux. fuel source and gently push the float up to see if the fuel stops. For adjustable style floats, the best way to check the float level is to w/ an aux. fuel source. Hold the carb in the position as is on the scooter, hold the bowl on and let it fill. It should end up about 2/3rd.s full. Bend the metal tang carefully to achive this.
This is all very straight forward, but the area that non-experts have trouble in, is the pilot(or idle or low-speed)circuit.
It is comprised of, very sm. diameter passageways drilled into the carb bodies during the machining process. These passageways are drilled from several angles and their intersections are perpendicular or even acute angles and precision in this process(including the removal any left over flashing) is absolutely critical for a smooth idle. I don't believe the non-Japanese manufacturers have this down pat and this is the reason the Japanese units are superior.
There are two entry/exit points in the low-speed circuit;
One metered orifice(jet) in the float bowl and one non-metered orifice located in the air stream. It is seen as a very sm. hole in the belmouth(air box side) of the carb.
There is also a mixture adjust screw, which on these carb.s regulates fuel(located on eng. side of carb.). With this screw removed. we have the the third orifice of three that we will focus our attention on.
One must make absolutely sure that this circuit is FREE and CLEAR and to do this, three things are needed, a sm. fine point scribe, cleaner spray and/or compressed air and good hearing.
Blocking off one hole with the scribe, spray though one other and look/hear for the cleaner/air exiting the remaining hole. Repeat for all possible combinations.
The low-speed jet must be clear as well, but due to the sm. size of these jets, it's hard to know for sure. Experience is needed here and if in doubt, buy a new one(one size larger would probably be right for most of the models here).
The mixture screw will sometimes have either a "blind plug" or a limiter cap. The blind plug is removed by drilling a Sm. shallow hole(don't drill though into the screw), installing a wood screw and pulling in out with ViceGrips. The limiter cap protrusion can be cut off with a Dremel tool) I have been known to use a hefty pair of sidecutters when in a hurry, but care is needed here as to not snap off the whole head.
When re-installing the screw, gently seat it and back it off 3 full turns. Once the eng. is warm and the idle set a little low, slowly turn the screw in till the idle drops. Then back it off 1/2 a turn and you will be in the ball park. On most stock eng.s, the screw will end up between 1 and 2 turns out. Never more than 3 turns out(it can fall out). If it wants to be less than 1(larger jet) or more than three turns out,(circuit still obscured) something is still wrong.
itistheride.boards.net/index.cgi
These basic methods apply to carb cleaning, but also have relevance in trouble-shooting defective "made in China" carb.s(defective new Japanese carbs are unheard of).
The area we will focus on is the idle or low-speed circuit, but I will briefly touch on a couple things first.
Most of these scooters are still too new, but carb.s in which gas has sat. for a period of time, can become quite a smelly, green mess. The worst of them had their condition worsened by a leaky petcock or vac. gas valve that would allow the bowl to keep re-filling while the fuel was evaporating away. Cleaning all the parts can get quite laborious and in the end, one usually just scrapes away most of the residue with a sm. flat screwdriver and sm. wire(brass) brush.
It seems like everyone one has their favorite carb cleaner, but in most cases, any carb spray can will work. Really nasty units will need to be soaked and in a sm. %, need to be taken to the shop to be soaked and agitated. How to know? Well that's what we are getting to, but first;
Float levels- Some of the floats on these scooters are plastic, non-adjustable and rarely leak. What is a concern, is the ability of the float needle to stop the flow into the bowl. Simply connect a aux. fuel source and gently push the float up to see if the fuel stops. For adjustable style floats, the best way to check the float level is to w/ an aux. fuel source. Hold the carb in the position as is on the scooter, hold the bowl on and let it fill. It should end up about 2/3rd.s full. Bend the metal tang carefully to achive this.
This is all very straight forward, but the area that non-experts have trouble in, is the pilot(or idle or low-speed)circuit.
It is comprised of, very sm. diameter passageways drilled into the carb bodies during the machining process. These passageways are drilled from several angles and their intersections are perpendicular or even acute angles and precision in this process(including the removal any left over flashing) is absolutely critical for a smooth idle. I don't believe the non-Japanese manufacturers have this down pat and this is the reason the Japanese units are superior.
There are two entry/exit points in the low-speed circuit;
One metered orifice(jet) in the float bowl and one non-metered orifice located in the air stream. It is seen as a very sm. hole in the belmouth(air box side) of the carb.
There is also a mixture adjust screw, which on these carb.s regulates fuel(located on eng. side of carb.). With this screw removed. we have the the third orifice of three that we will focus our attention on.
One must make absolutely sure that this circuit is FREE and CLEAR and to do this, three things are needed, a sm. fine point scribe, cleaner spray and/or compressed air and good hearing.
Blocking off one hole with the scribe, spray though one other and look/hear for the cleaner/air exiting the remaining hole. Repeat for all possible combinations.
The low-speed jet must be clear as well, but due to the sm. size of these jets, it's hard to know for sure. Experience is needed here and if in doubt, buy a new one(one size larger would probably be right for most of the models here).
The mixture screw will sometimes have either a "blind plug" or a limiter cap. The blind plug is removed by drilling a Sm. shallow hole(don't drill though into the screw), installing a wood screw and pulling in out with ViceGrips. The limiter cap protrusion can be cut off with a Dremel tool) I have been known to use a hefty pair of sidecutters when in a hurry, but care is needed here as to not snap off the whole head.
When re-installing the screw, gently seat it and back it off 3 full turns. Once the eng. is warm and the idle set a little low, slowly turn the screw in till the idle drops. Then back it off 1/2 a turn and you will be in the ball park. On most stock eng.s, the screw will end up between 1 and 2 turns out. Never more than 3 turns out(it can fall out). If it wants to be less than 1(larger jet) or more than three turns out,(circuit still obscured) something is still wrong.