Topic: Emulsifier tube direction?

[BigBird]

Does the orientation of the emulsifier tubes other than up/down affect anything, and if so, which way angles forward?

Working on cb550f w 069A carbs

Thanks

[flybox1]

Yes, it does matter, the OPEN end with the waist band is inserted into the carb body first, like the top of the one pictured

[BigBird]

Thanks for the response. As I tried to state in the question I am aware of orientation of which way is up. I am asking if the tube should be place in a specific rotation, in relation to which way is forward on the bike.

My logic suggests that, for example under acceleration, the fuel would be forced backwards, and should influence the flow into the tube. Does anyone have a thought on wether the holes of the emulsifyer be facing forward/backwards or perpendicular to that?

[dbbrian350F]

I can't imagine that would matter nearly as much as getting all those little holes cleaned out. 

Like this

[Kenzo]

Thanks for the response. As I tried to state in the question I am aware of orientation of which way is up. I am asking if the tube should be place in a specific rotation, in relation to which way is forward on the bike.

My logic suggests that, for example under acceleration, the fuel would be forced backwards, and should influence the flow into the tube. Does anyone have a thought on wether the holes of the emulsifyer be facing forward/backwards or perpendicular to that?

If I'm not mistaken those holes provide air not fuel...correct?

Cheers,
Kenzo

[HondaMan]

Those holes aerate the fuel and help lift it up to the throat of the carb (at the top of the emulsifier tube). When the engine is running, this tube is immersed in fuel that was pushed up from the float bowl, because the air pressure in the float bowl is still and at higher pressure than the moving air in the carb throat. These little holes "bubble" air into the fuel column, air which is supplied from the bell-shaped area at the back of the carb: this air is at about 10-40% higher pressure than the air in the throat, but 90-60% of the pressure in the float bowl (depending on throttle opening). Thus...then the fuel gets pushed up the emulsifer tube by the bowl, it gets bubbled (aerated) by the air entering these little holes, so it can arrive at the mainjet in an almost steam-like state for the engine to suck up.

The holes nearest the top of these tubes aerate the low-speed operation. As the throttle opens more, the fuel level in this tybe drops accordingly, being limited by the mainjet, and aerates it about the same amount because fewer holes are then "under water", so to speak. At full throttle, this tube is nothing but bubbles of air in fast-moving fuel.

...and now you know how these carbs work! The idle circuit is identical, just smaller.

[jonda500]

Those holes aerate the fuel and help lift it up to the throat of the carb (at the top of the emulsifier tube). When the engine is running, this tube is immersed in fuel that was pushed up from the float bowl, because the air pressure in the float bowl is still and at higher pressure than the moving air in the carb throat. These little holes "bubble" air into the fuel column, air which is supplied from the bell-shaped area at the back of the carb: this air is at about 10-40% higher pressure than the air in the throat, but 90-60% of the pressure in the float bowl (depending on throttle opening). Thus...then the fuel gets pushed up the emulsifer tube by the bowl, it gets bubbled (aerated) by the air entering these little holes, so it can arrive at the "mainjet" in an almost steam-like state for the engine to suck up.

The holes nearest the top of these tubes aerate the low-speed operation. As the throttle opens more, the fuel level in this tybe drops accordingly, being limited by the mainjet, and aerates it about the same amount because fewer holes are then "under water", so to speak. At full throttle, this tube is nothing but bubbles of air in fast-moving fuel.

...and now you know how these carbs work! The idle circuit is identical, just smaller.

Don't you mean the fuel would arrive at the throat? (it's already been sucked up the main jet!)John

[mystic_1]

Thanks for the response. As I tried to state in the question I am aware of orientation of which way is up. I am asking if the tube should be place in a specific rotation, in relation to which way is forward on the bike.

My logic suggests that, for example under acceleration, the fuel would be forced backwards, and should influence the flow into the tube. Does anyone have a thought on wether the holes of the emulsifyer be facing forward/backwards or perpendicular to that?

You're over thinking things.  In such a small enclosed space, there's no where for the fuel to be forced TO, really, and even if fuel was pulled away from the front-facing holes, it will be pulled towards the rear-facing holes, so it's all a wash.

If it made any real difference, the parts would be keyed to only fit together one way.

mystic_1

[HondaMan]

Those holes aerate the fuel and help lift it up to the throat of the carb (at the top of the emulsifier tube). When the engine is running, this tube is immersed in fuel that was pushed up from the float bowl, because the air pressure in the float bowl is still and at higher pressure than the moving air in the carb throat. These little holes "bubble" air into the fuel column, air which is supplied from the bell-shaped area at the back of the carb: this air is at about 10-40% higher pressure than the air in the throat, but 90-60% of the pressure in the float bowl (depending on throttle opening). Thus...then the fuel gets pushed up the emulsifer tube by the bowl, it gets bubbled (aerated) by the air entering these little holes, so it can arrive at the "mainjet" in an almost steam-like state for the engine to suck up.

The holes nearest the top of these tubes aerate the low-speed operation. As the throttle opens more, the fuel level in this tybe drops accordingly, being limited by the mainjet, and aerates it about the same amount because fewer holes are then "under water", so to speak. At full throttle, this tube is nothing but bubbles of air in fast-moving fuel.

...and now you know how these carbs work! The idle circuit is identical, just smaller.

Don't you mean the fuel would arrive at the throat? (it's already been sucked up the main jet!)John

The "throat" here refers to the area under the front edge of the slide, back as far as the needle jet opening (above 1/8 throttle). The engine only sucks in the fuel that was squirted up the needle jet by the float bowl's positive pressure (relative to the lower pressure in the throat). Many people think about this 'backwards', as the engine doesn't really do anything but drink in the gas mist the carb puked up the needle jet!

[Don R]

 I had a lectron once with a clear float bowl, it was on a single cylinder but it was amazing to see the fuel foam up in the bowl when the engine revved up, it had a high speed jet too with a clear line on it. We ran a foam sleeve over the fuel pickup to try to keep it from sucking air.
 It would be amazing to see how the emulsion tube works in close up slow motion.

[Killer Canary]

Just curious; the top part of the emulsion tube which projects into the carb throat on my MT250 is flush with the carb body for half of it's diameter with only a180 degree skirt actually projecting into the carb body. This skirt broke off while I was removing the emulsion tube for cleaning.
What adverse effects can I expect from this?

[Kenzo]

Just curious; the top part of the emulsion tube which projects into the carb throat on my MT250 is flush with the carb body for half of it's diameter with only a180 degree skirt actually projecting into the carb body. This skirt broke off while I was removing the emulsion tube for cleaning.
What adverse effects can I expect from this?

SWAG, less than perfect or designed fuel delivery, enough to make a difference? Maybe, maybe not...

Basically the venturi effect of the air that moves over the top of the opening causes a low pressure and draws the fuel into the carb throat. The shape, size, position, etc...all determine the pressure differential and fuel flow.

Not familiar with that bike but the carb can probably be adjusted to compensate for the issue.

Cheers,
Kenzo

[grasscutter]

Don't the emulsion tubes have a centering tab?  They can only go in one way?

[Kenzo]

Don't the emulsion tubes have a centering tab?  They can only go in one way?

Look at the pics above...it can only be inserted and seated properly in one direction. The smaller end first(inserted from the bowl side) and when seated properly just flush or a mm so into the carb throat.

The original question was about the rotational orientation of the emulsion holes on the side of the tube.

Cheers,
Kenzo

[grasscutter]

Please forgive my ignorance specifically on the CB550 carbs.  I'm truly asking a question. 

That was my point with my question: If it only goes in one way (as previous commenters stated), then how do you adjust or change the 'hole orientation'? 

Don't the CB550 carbs have a 'centering tab'? 

Like this one:

[Duanob]

As said above it doesn't matter. The tiny emulsion holes only suck in air to mix with the fuel being sucked up through the main jet into the inside of the emulsion tube. In Honda 4's case there is no 'orientation' for the air holes. And that's not a 550 emulsion tube.

[grasscutter]

There's no centering slot.   Got it!

[HondaMan]

Please forgive my ignorance specifically on the CB550 carbs.  I'm truly asking a question. 

That was my point with my question: If it only goes in one way (as previous commenters stated), then how do you adjust or change the 'hole orientation'? 

Don't the CB550 carbs have a 'centering tab'? 

Like this one:

On carbs with 'direction-sensitive' emulsion tubes, there is usually another feature on those tubes that have to orient to something else in the carb. Sometimes, in Mikunis, this may be the "power vent" hole from the power jet, which puts its extra fuel up into the needle jet. The simpler OEM carbs in the SOHC4 bikes don't have this feature.

[HondaMan]

I had a lectron once with a clear float bowl, it was on a single cylinder but it was amazing to see the fuel foam up in the bowl when the engine revved up, it had a high speed jet too with a clear line on it. We ran a foam sleeve over the fuel pickup to try to keep it from sucking air.
 It would be amazing to see how the emulsion tube works in close up slow motion.

Yeah, the single-cylinder, single-carb setups like these can get real turbulent! The spitback during overlap cycle is the culprit, and with wide-duration cams it gets to be a nuisance. The 2-strokers suffer it much worse than the 4-strokers, too, because the crankcase pressures those carbs are feeding are like a ferris wheel with fins(!). This usually limits the upper end of the mixing speed to around 6500-7000 RPM without adding something like reed valves or rotary valves in strokers, just to get the carbs to still work.