Carb Cleaning 101

[motomech]

I've taken a look at the carb cleaning Wiki here and it seems to me that it's somewhat difficult to read though and misses out on a crucial point, namely, making sure that the low-speed circuit is free and clear.
For what it's worth, here's a short tutorial that might be considered an addendum, but not a replacement to the Wiki.
The area we will focus on is the idle or low-speed circuit, but I will briefly touch on a couple things first.
Carbs on scooters that have 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 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 work. Really nasty units will need to be soaked and with scooters that have sat a long time, 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- Most 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 fuel flow into the bowl. Simply connect a aux. fuel source and gently push the float up to see if the fuel stops. Most float needles[called seat needles] used with plastic non-adjustable floats have a spring-loaded plunger where they come into contact with the float tang. Make sure that these plungers move freely.
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 to their Chinese counterparts.
There are two entry/exit points in the low-speed circuit;
One metered orifice(the smaller of the two jets visible when looking at the bottom of the carb) 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 and it's these three holes 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[using the straw] and look/hear for the cleaner/air exiting the remaining hole. Repeat for all possible combinations. If, while checking these combination when spraying the carb cleaner in, it does not flow out, compressed air may clear the blockage. What's needed here, is the type of air nozzle with the rubber tip. Remember, air should flow in and out of all three of these holes.
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 speed 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 the engine wants to see the mixture screww more than 2 1/2 turns out, the low-speed mixture circuit is still obscured or a larger jet is needed to meet the engine requirements.
EDIT-On scooters the idle speed can be set according to RPM as listed in that model's service manual.
An alternative method involves raising the idle speed to the point where the drive wheel start to rotate and then back it off from there.

[abreen89]

I've taken a look at the carb cleaning Wiki here and it seems to me that it's somewhat difficult to read though and misses out on a crucial point, namely, making sure that the low-speed circuit is free and clear.
For what it's worth, here's a short tutorial that might be considered an addendum, but not a replacement to the Wiki.
The area we will focus on is the idle or low-speed circuit, but I will briefly touch on a couple things first.
Carbs on scooters that have 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 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 work. Really nasty units will need to be soaked and with scooters that have sat a long time, 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- Most 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 fuel flow into the bowl. Simply connect a aux. fuel source and gently push the float up to see if the fuel stops. Most float needles[called seat needles] used with plastic non-adjustable floats have a spring-loaded plunger where they come into contact with the float tang. Make sure that these plungers move freely.
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 to their Chinese counterparts.
There are two entry/exit points in the low-speed circuit;
One metered orifice(the smaller of the two jets visible when looking at the bottom of the carb) 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 and it's these three holes 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[using the straw] and look/hear for the cleaner/air exiting the remaining hole. Repeat for all possible combinations. If, while checking these combination when spraying the carb cleaner in, it does not flow out, compressed air may clear the blockage. What's needed here, is the type of air nozzle with the rubber tip. Remember, air should flow in and out of all three of these holes.
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 speed 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 the engine wants to see the mixture screww more than 2 1/2 turns out, the low-speed mixture circuit is still obscured or a larger jet is needed to meet the engine requirements.
EDIT-On scooters the idle speed can be set according to RPM as listed in that model's service manual.
An alternative method involves raising the idle speed to the point where the drive wheel start to rotate and then back it off from there.

did you see the step by step pictures??? http://hondaspree.net/wiki/index.php5?t ... ture_Guide

[motomech]

Yes I did, but as I stated in the first sentence, it completely glosses over the critical procedure of making sure the low-speed circuitry is clean.
It says; " And make sure everything is clean. Now take compressed air and blow it all out."
You can clean and polish the inards of a carb til the cows come home, bit if those pilot/idle passageways are not clean, the motor will never start and idle well.
The smaller the motor, the smaller the carb.
The smaller the carb, the smaller the internal passageways.
The smaller the passageways, the harder they are to get clean!
If the moderators think this contribution is if no value, they can remove it.

[abreen89]

Good Job I agree good instructions shouldn't assume u have any prior knowledge of the task being instructed.

[motomech]

Although I haven't yet read back though the repairs sections that far, it seemed to me there was not a high rate of success in cleaning these little carbs , hence many looking for new replacement units.
Really, in my experience, no matter how nasty the carb is, only about 1 in 10 should result in throw-a-ways. And even some of those could be saved by a shop with an agitating carb cleaning machine.

[mousewheels]

Thanks for the write-up. I agree, carb info is spread around. Getting a full write up together with pics would help out. Will work on integrating your write-up with existing + new pics this fall/winter...

[Dani50]

motomech, do you have to take carb apart and remove all the o-rings and gaskets before you soak it?

[swimmingfree]

motomech, do you have to take carb apart yes and remove all the o-rings and gaskets before you soak it? yes

you shood never put nothing but metal in carb cleaner..
swimmingfree