Question about function of the emulsion tube

Turbota · #1 15th February 2005

I got a question for anyone here that has good understanding of the CV emulsion tube.

I know it is the main jet holder, but those very small holes drilled in the side of it must have a very good purpose.

I compared the stock emulsion tube from my 04 1200 with the DynoJet emulsion tube. The stock tube has 2 separate rows to 5 holes each, and 2 separate rows of 3 holes each, for a total of 16 holes drilled down the length of it.

The DynoJet tube only has 2 holes drilled in it. These holes are very small and no larger in diameter than the holes drilled in the stock emulsion tube.

Anyone really know what the function of these small holes is? ... Certainly DynoJet feels that there are too many holes on the stock tube since they only use 2 holes.

Thanks,

BTW ... Someone posted once that a stock H-D main jet won't screw into the DynoJet emulsion tube ... That's a fact! The threads are finer on the DynoJet main jets and emulsion tube than they are on the stock main jet and emulsion tube ... Can't combine the two parts.

IronMick · #2 16th February 2005

When the liquid fuel is drawn thru the emulsion tube it passes thru the holes and becomes a fine mist mixed with a certain amount of air then it can be burned by the spark. The holes create the mist.

I do not know why fewer would be better than many [?]. Someone else will chime in here for sure ...

xena · #3 16th February 2005

I bet Stevo knows the hows and whys. I'm interested as well.

stevo · #4 16th February 2005

This is a VERY advanced area I havn't delved into for many years.......I'll get back into it later when I start back on the development path when mine gets together at 88"

Basicly the emulsion tube in a CV is where fuel and air mix together to form an emulsion before exiting the carb and heading off down the intake tract....

OK ...CV basics 101

The low speed/idle circuit is independant of the main circuit... it gets by fuel thru the pilot jet and the air from the slow speed air jet in the front of the carb...
the fuel comes out of the small holes at the bottom of the carb venturi just behind the throttle plate....

As the throttle plate is opened further the main circiut comes into play...

fuel enters the bottom of the emulsion tube thru the main jet.....

Air enters thru the main air bleed jet in the front of the carby...

the air and fuel are mixed into an Emulsion in the emulsion tube before it passes up the tube past the needle jet and needle into the carb venturi and down the intake chasing after the idle circuit fuel....

the size, number and position of the holes in the emulsion tube effect the fuel delivery....

More holes = more air = leaner mixture
more holes at the top = leaner mixture at low speeds
More holes at the bottom = leaner mixture at hogh speeds

If you change emulsion tubes you need to put a matching needle in and it will also have an effect on the main jet size and quite often the pilot circuit thru the just off idle response

needles, needle jet, emulsion tube (size, position and amount of holes) main air bleed size and main jet are all closely linked......changing one can affect the others...and ALL have an affect on the fuel delivery to differing amount.

And we havn't even touched the slide yet

This is an area that is useful to understand with the S&S carb as by changing to an adjustable intermediate air jet it's possible to fine tune the mid range, an area that tends to be rich on S&S's

sportsterrific · #5 16th February 2005

Hey Stevo, thanks for the carb lesson. I just did my rejetting and when I pulled out my main jet, the emulsion tube came out with it. My dealer had given me a 170 main that wouldn't fit. When I went back to the shop, he realized he had given me a Dynojet main, and explained that the emulsion tube was different, but I didn't ask him for details. (I had to go back there to get some other stuff and they are literally 5 minutes from me so I wasn't too pissed off).
I, like probably 90% of us, find carbs a mystery, and basically did my rejetting following the instructions found on old XL forum. But you explained the function of the emulsion tube pretty well, and now I actually know what I was dealing with!

ed_in_az · #6 16th February 2005

Wow, Stevo, that was a great carb lesson.

Up until right now I guess I took messing with carbs on my bikes for granted. Now I can see more clearly how a subtle change can make a drastic difference. That's probably why I could never get my dual carbed Suzuki quite perfect. It was really close, ran well, but never perfect. I just got tired of pulling everything apart and changing jets, over, and over, and over. I'm glad the Sporty has only one carb.

cantolina · #7 16th February 2005

Quote:

Originally Posted by ed_in_az

Wow, Stevo, that was a great carb lesson.

Up until right now I guess I took messing with carbs on my bikes for granted. Now I can see more clearly how a subtle change can make a drastic difference. That's probably why I could never get my dual carbed Suzuki quite perfect. It was really close, ran well, but never perfect. I just got tired of pulling everything apart and changing jets, over, and over, and over. I'm glad the Sporty has only one carb.

Agreed...I have a 4 CARB! Yamaha Maxim 1200 sitting in storage for that very reason! lol

It will probably stay there till someone takes it off my hands...I'm not playin with it....

sportsterrific · #8 16th February 2005

I was talking about my carb with my metric-riding buddy last night. He used to have a V-max and he did carb work on it & it just never ran right after he rejetted. I can't imagine trying to properly jet and synchronize 4 carbs, especially tucked away in the 'V' like that.
Cheers to single carbs!

stevo · #9 16th February 2005

There's a damn sight more to it than what I just explained..... I've been doin this for years now and I'm still learning more almost every time I get a different vehicle to play with...

Ya need to understand the basics before ya go playing with things tho....or ya just flying blind and guesswork is no way to do anything

I do jap multis as well and yup it sure is easier to play with a Harley....

Most modern (pre fuel injection) jap multis are VERY fickle on the tuning circuits....

Putting a less restrictive air cleaner on (like a K&N), often leans the circuit out BUT it can cause rich spots as well due to subtleties in the harmonics, if the intake diameter is changed....
If you imagine a restrictive air cleaner is like patially putting your hand over the carb.....it will suck more fuel...so less restrictive = less suck = lean.....so ya often gotta put a bit more fuel in thru the whole circuit
Add a different exhaust system to the and you can have rich spots due to exhaust harmonics...and then ya gotta take fuel out in different areas..

And don't try playing with Jap mutlis untill ya get some vacuum gauges..... it's no different to a Harley....just gotta match 'em all......it just takes a LOT more time....and patience.

Turbota · #10 16th February 2005

Stevo ... Thanks for the education about the emulsion tube