I am doing an experiment with the stock carb.
I had the emulsion tube modifed to better atomize fuel.
It is working very good.
I then had 3 springs made at different rates to match the fuel delivery change.
One spring produced tons of torque but did not open all the way for good top end.
The second spring still has good torque and will rev out.
The 3rd spring definitely opens very fast. My problem is that it opens too fast
and even with the needle all the way up, it is alittle lean.
If I run a larger main the mid is great, but then I flood out at top.
If I can get more fuel in mid range and lean out at top this will be the best I have ever got the stock carb to perform.
Now I understand why MrHP says to keep the airbox lid on. To have great torque and to be able to get the slide to open
all the way you need negative pressure to raise the slide.
I am using a modified emulsion tube so as to raise more fuel and have the airbox lid off to get the most hp at top.
The #2 and 3 spring have the same force as the stock spring at rest, but has less tension when totally open. Thus to allow the slide to open all the way without negative pressure(air lid on).
Does anyone have a dynojet needle they do not use anymore so that I can
finish doing this experiment I started? I will be willing to buy, I just don't need the whole kit.

 

I messed around with the stock carb quite a bit and wanted to do alot of the things you are doing before I gave it up. I'd like to share some of my thoughts and findings.
Different years DS's have different spring rates, you can order a few to experiment with, ther'e just a couple bucks a piece. I thought of making a spring rate tester.
MrHP left the airbox lid on to help create a vacuum that would help lift the carb vacuum slide. This is like shoving a plug into the exhaust because you don't understand rejetting.
The K&N needle or (Dynojet) has awesome bottom end characteristics. I switched back and forth at least 5 times and could never get the stocker to perform like the K&N.
With a selection of stock needles you can flat file a D shape on the end to richen top end jetting, you could get creative and make your own needle profiles.
There used to be alot of talk of drilling out the air bleed holes in the bottom of the slide, this came from old posts where the same carbs was used on Harleys. Mikuni has chanded the size and amount of holes since then. I would try restricting the hole size to get more vacuum effect on the slide.
The biggest problem that I could see with the stock carb was the tendency of the slide to bounce at wide open throttle. I think more vaccum on the slide would help this.
How did you mod the emulsion tube? drill it for air bubbling or put something on the top to spread the fuel faster?

 

Well I hope I am reading your post correctly, mysteried. You mention MisterHP left the lid on to help create better vacuum and that you don't agree with this theory.

I would tend to agree with you, if that is your statement. The lid will have no effect on the vacuum inside the slider. The vacuum on the slider is determined by the amount of air flowing thru the carb. Air flowing past a hole will cause a vacuum inside the chamber the hole is connected to. The more air that flow thru the carb, the more vacuum it will create in the slider. Adding a restriction to the airflow (lid in place), will cause less air to move thru the carb, and prevent the slider from opening correctly. It might solve the problem of an incorrect mixture, but you are restricting the airflow, to fix a slider and needle problem. In the process of doing this you are restricting power output, especially at high RPM, when you need massive amounts of air as well as throttle response.

I personally am not a big fan of cutting the spring. You need to address the tension, not the length of the spring. By cutting it you are reducing the length and the tension. Has anyone tested the reaction of the slider with a cut spring? In cutting the spring you change the length and in doing so, might mess up the way the slider moves. With the spring shorter than normal, it might not have the right length and tension to hold the slider in the right place. This might cause it to move erratically and cause flat spots or strange mixture problems, since the needle is not designed to work with the modified spring. Most people will test the mods on the dyno, but they test it to see power output increase at full throttle. What they do not test is the way the slider reacts with a fixed throttle opening.

Another way you can change the way the slider reacts is by changing the hole size at the bottom of the slider. This will give you more or less vacuum. Bigger holes will cause the slider the react quicker and open larger, while smaller holes will tend to make it move slower and open less. There is a fine line between the right holes size and spring tension. With a big hole the slider will move quickly up and down. Great for drags, but it might cause other problems. The air flowing thru the carb is not a constant flow of air. You have air waves or pulses. These pulse move at very high speeds, but keep in mind that the speed and air volume varies and that it is not a constant. The slider relies on this airflow to determine how much it will open. A slider that reacts too quickly will cause the slider to move up and down during the intake process and will result in a flutter. This flutter is not good for the air intake. A slider with a smaller hole will move slower and might have a more constant opening, but it might be a smaller opening than the slider with a bigger hole. You need to find the right balance.

Think of it this way. The hole size is like a shock absorber, make it to weak (big hole) and it will cause the spring to bounce. Make it to small and it will take a long time to open correctly. The spring tension determines the pressure or the vacuum required to move the slider. Think of the slider as setting up your bikes suspension for whoops. You need to suspension to give you the right amount of travel (spring length and tension) and the right amount of damping and rebound (hole size). The needle is the last thing you need to worry about. All the needle has to do is give you the right fuel mixture for the slider opening and it should be the last thing you do when it comes to the way the slider works.

When you change the spring tension you need to confirm that the slider is opening up correctly under full throttle. I have never tried this, but you should be able to use a mirror and flashlight, maybe a video camera, while on a dyno, to look down the carb to see that the slider is opening 100% under full throttle. If it is not opening 100%, you are loosing airflow into the motor and need to try something different.

 

I cut the springs on both my DS's and my buddys DS and they have been like that for years with no problems. We switched back and forth from stock to cut and the perfomance way very noticable. I am a true beleiver in this no cost mod and would recommend it to anyone. My DS had a hard time doing a wheely by rolling on the throttle, know you hit the throttle and the front end just pops right up.

 

The reason I had special springs built was to control the slide flutter.
By having the spring equal to or even alittle stiffer at rest, controlled low speed flutter.
At high speed I wanted a spring with tension greatly reduced so it had minimum flutter.
The balance tube actually has a very important function. When the motor is going through the exhaust stroke,
the reversion of incoming air pressurizes in the snorkel, thus backs up in the balance tube and causes the slide to rise.
This effect along with a lower spring rate at high speed keeps the flutter to a minimum.
I drilled out the vacuum ports to allow the slide to come down as normal when off throttle.
The higher spring rate at rest with the better atomized fuel, generates a very high velocity at low speed that results in huge torque gains.
You can floor the throttle at idle and have instant throttle response.
Because of the very high velocity I then, when under drag conditions, have a lean spot in mid range.
That is why I need a diffent needle to calibrate the fuel requirements of this experiment.
The emulsion tube atomizes very good for bottom and half way thru mid, then just before going completely into the main jet range, has a flat spot.
By the way, I want to thank all for having this review at this high level. Great responses.
That is how we think outside the envelope and develop new theories that may make us DS lovers unique.

 

Freez, that is one informative post you have going on. I shouldn't say that I know for sure what MrHP was thinking but I am sure that restricting airflow to an engine can't be a good thing. I just happen to believe there is more to be had from the stock carb. Alot of people jumped on the TM45 and Lectron bandwagons without fully delving into what could be done with the stocker.
I considered restricting the hose size of the cv vent or even putting a one way valve in, only partly operational of course, to stop some of the wot slide flutter.
While I'm sure my carb could be tuned better, I couldn't find any more stock DS's to beat me and lost interest. A few other helpful items were a custom intake tube and port matching the intake and the exhaust gaskets, and advancing the timing at the pick up.
Oldmanracing, what did you do to the E-tube? Have you considered your own needle profiles? Possibly even taking a little off the tip and file it to a point? Wouldn't that put you into the main sooner?

 

1st of all, do not restrict the CV vent. Some people have a misunderstanding about how that vent works. Some people believe that if you remove the vent pipe and open it up that the carb will not work. It is actually the opposite of what will happen. I did lots of work on the raptor, but the DS uses a similar carb and is made by the same company.

If you restrict the vent you slow down the reaction time of the slider. This might fix your flutter problem, but it will mess up your acceleration. What we found on the dyno is that smaller holes will reduce HP and torque output during full throttle acceleration. Especially between 3000 and 5000 RPM. Open the vent to the max and you gain very good acceleration and a good power increase during the acceleration process.

The slider works on vacuum. Above the slider you have a diaphragm and a chamber where the vacuum is generated. This vacuum “sucks” the slider up (opens the carb to flow more air). The vent feeds an area / passage under the diaphragm of the slider. When the vacuum above the slider pulls the slider up, the chamber underneath needs to fill up with air. Restricting this air will cause the slider to reacts slower. You might fix a flutter, but in the process you are also slowing down how quickly the carb can open when you hit the throttle wide open.

The best is the install a little breather filter onto the vent hole. For you that don't know this, the Predator uses the exact same carb as the DS and it uses this breather principle. On the DS and the Raptor the vents connect to the rubber intake between the carb and the air filter. In both cases the hole is 90 degrees to the flow of air into the carb. 90 degree flowing air will create a vacuum inside the hole leading to the vent, plus if you run with a restrictive filter or the lid in place more vacuum is generated inside the vent passage. This means that you will end up with a vacuum under the slider diaphragm. In the end you have two vacuums competing with each other. One above the diaphragm and the other underneath it. This can also be a source for the flutter, because the vacuum under the slider will try and pull the slider closed.

Try removing the vent hose and see how this affects the performance. You might find you gain some throttle response and acceleration in the process.