We need to get the DS on a Air/Fuel analyser to see what happens at the top end. Why do you guys find that the motor ref out better with the lid on. The only reason I can think about is to little or to much fuel. In theory the open lid should add more flow. With the lid on, you are restricting the airflow, or.... it reaches a tuned state, where a resonation actually adds a bit more flow, that you don’t get without the lid on.

I would be amazed if it does the resonation bit, since the air cleaner inside the airbox, will tend to absorb the resonations. Resonator boxes have a clean/empty box, with the air cleaner at the intake snorkel to the airbox.

 

Freez and OMR,

When I started modifying the intake and exhaust on my DS, the first thing I had to do was change the gearing. With the choked stock setup, the quad did not have the midrange to pull higher gearing, it would bog and fall off the pipe if you weren't wide open on the throttle. Even still, with 20" tires, I managed to pull 78mph (on GPS) out of my 2002 Baja. When I first started modifying the exhaust, as Freez stated, the quad would rev through the first two gears as fast as I could shift it. I then changed to 17/38 gearing and this helped in the bottom three gears, but there seemed to be a big jump to fourth and fifth, like it couldn't pull it. It was geared for 88mph, but all I could get out of it was 81 on GPS. After changing to DJ needle and main jets, this thing again revs like it was geared back to stock. It pulls so hard that for the endurance racing I plan on doing, I'm wondering if I should be dropping a tooth or more off the back sprocket. I haven't even done the mods to the vacuum tube or slide and the thing hits so hard in the midrange that the backend wants to pass the front in the corners. I'm running 20" Razor II's in the back, almost new condition, very heavy tire. I will use the GPS this weekend to test if I am indeed able to do 88mph, my gut says I am because I was on the rev limiter testing on the road yesterday.

OMR, doesn't a 14 tooth front sprocket pretty much eliminate the first two gears in your tranny. I found that I had to shift way too much, especially if your son is motocrossing his quad.

Freez, I will be trying the vacuum tube mod first, as you suggested. Then I will change the vacuum tube back and do the slide mod, see which one makes a better difference. Then of course, do them both together.

 

Some more Maintenace suggestions

DS Float Maintenance and Pilot Cleaning

1- If you have inconsistent main jet setting, float height adjustment may be the problem. If you find your jetting always rich, that is, after a trail ride the plug
looks gas soaked, and black is the color on end of plug and porcelain is dark brown; adjustment to the float is required.
I feel that the factory spec is a little on the rich side. The spec is 10mm(.394).
Trying to bend the tab and hit this dimension is like hitting a moving target.
I have found more consistent results using this procedure:
With float bowl cover removed, turn carb upside down.
Note that the floats are formed with a crowned end surface. How can you take a measurement off a surface that is not flat - You can’t.
But there is a edge just below this crown that is straight.
I take a first measurement to this edge, at the pinned end. Write down reading
I take a second reading to this edge, at the unpinned end. Write down reading.
Subtract second reading from first reading.
My Spec: 0 to 3/32(.090) That is - The second reading should be equal to first reading or lower to as much as 3/32(.09).
I have used this spec for 3 years and have not had inconsistent readings or plugs fouling out.
If you are doing power testing runs and find that top end is inconsistent. That is, sometimes strong and sometimes flat. Float height is the issue.


2- Pilot Cleaning
If your motor starts hard or not at all. Pilot circuit is dirty or clogged.
Remove pilot screw, be careful not to loose small spring and washer.
With a air compressor, that has a rubber tipped nozzle, blow air into the
orifice that the pilot screw was removed from. Spray alittle carb cleaner
into orifice and blowout again. Gas has a tendency to dry-up and leave deposits
around the pilot air/fuel passage. Try to clean twice a year or when having starting problems.

 

Just to add on to what OMR was saying.

Float level is critical and should be checked before you do any jetting. With it out of spec, your jetting will be off.

I do most of my work on raptors, and the float level from the factory is wrong on all raptors. They are about 3mm to high. By setting them up as per the carb manual, I gain about 2 to 3HP. Yes, nearly 10% more power, by adjust the float level alone and not touching a single jet or the needle clip position.

It also gives the bike about 500 RPM more on the top end before the HP start dropping and before you need to change gears. The extra HP gain, and 500 more RPM, makes a big difference on how quick the bike accelerates. On a drag strip, this alone can add 2 to 3 bike lengths easy.

Anyway, the DS uses the same make carb as the raptors. The best way to check the float level is to use the clear tube method.

Look at the overflow fitting at the bottom of the carb. You will see it has a little pipe going towards the swing arm and it is a little screw, you can turn, to let out the fuel from the float bowl.

Now remove the drain pipe, and take it to a hardware/pet shop and ask them for a clear plastic tube, of the same inner diameter. They use them on fish tanks and so on. Make it about a foot or so long, the size does not have to be exact, but not shorter than a foot in length.

Go home and install this clear tube in the place of the drain pipe. Make sure it fits nice and snug, and point the other end of the clear tube, up. Try to keep the open end of the pipe as high above the float bowl and carb mating surface as possible, but make sure there is no dent or blockage from the pipe bending. I usually find a place I can hook the clear tube onto the carb and leave it there with the open end towards the sky.

Open the screw at the bottom of the float bowl, with your fuel pep **** open to allow fuel to go to the carb. The bike must be switched off. Fuel will start filling the clear tube and stop just above the split on the float bowl. If you see any bubbles in the clear tube, tap it lightly till they are all gone.

Now press the clear tube against the side of the carb and measure the fuel high from the carb and float bowl split or mating surface to the lower end of the fuel level “bubble” in the tube. It must be EXACTLY 4.5mm or 0.18" above the split. I state again... EXACTLY.. no 1mm higher or lower, EXACTLY! Make a mark on the carb itself to show you exactly where this 4.5mm is. If it is off, take your time to remove the carb, bend the tang on the float and repeat the process till you get this perfect. You will have to do very small changes to the tang. Even a light touch on the float, can throw the level off.

The clear tube is 100% accurate. Not all floats and fuel density are equal. I have found that on the dual carb on raptors, I have to bend the floats differently to balance the carbs. Racing fuel also sometimes require more bending on the tang, than normal fuel. The clear tube method will make sure the float level is perfect on your carb, no matter what float, of fuel you are running. Once you have it perfect, redo your jetting, and stick to the brand of fuel you did this test with.

You can do this test, without removing anything from the DS and only takes a few second to check it.

 

Any new updates on the stock carb mods?? I just tonight installed my Dyno Jet needle and main jet. Going to start with the tube mods first before I decide to re-drill the slide..also need to get a small filter for the balance tube..any suggestions?

 

We use a small filter that came from Unifilter.
It is installed on the end of the clear tube.
Measure the ID of tube and ask local dealer to look up
small male inlet filter. They are only 1 1/2od x 2 long(roughly).
We zip tied it. Measure the od of elbow and ask dealer for a
small vinyl cap. My son calls them mini condoms. You can use the clamp that
held the clear tube to elbow for the cap.
The filter comes with a clamp to install it.

Drilling the slide is a major step in improving
overall performance. I know that many people are thinking that they will be
damaging their slide and that they are expensive to replace.
There is a product called JB Weld that can be used to refill the two extra vacuum ports,
if you want to put back in stock condition. Around $3
When I first drilled the extra ports, I noticed only a small improvement, but I started with
only drilling 1/16". But I did notice that my top speed was greatly improved.
I then drilled to 3/32" and then I really felt the hit in mid and top.
By watching the tach I could see no hesitation from 5500 to 7000rpm.
From 7000 to 8000 it would show signs of going flat. I thought it was normal
and that I was over the hp peak.
To find out for sure that larger ports would help, I drilled to 1/8".
My son thought I had lost my mine, but I told him that we could always refill with JB Weld.
We assembled and my son took a ride, the look on his face said it all.
7000 to 8000rpm came to life.
Because I was trying to find a way to run without the lid, we always did a run with lid-on and then lid-off.
Till I drilled to this size, I could not get the performance at high rpm's, especially with lid-off.

I am still trying to find a way to run without the lid-on. There is more bottom power with lid-off, but
upper mid and top are way better with lid-on. I bought some turbulators and will see if they help top end with lid-off. Weather has been against me. Only have weekends to test.

Do the Mods has I have posted and you will never go back to stock.
As I find improvements , I will add to lists.

 

Freez and OMR,
Guys your information has been awesome. Right now I am really happy with how it is running. The dyno jet is dialed in. I will try the balance tube mod next, just have to find this filter. If that goes well then I will get the drill out [img]i/expressions/face-icon-small-wink.gif[/img]

 

Oldman, I've been keeping up with this and have applied 60% of your suggestions, but out here in the desert water is not a concern near as much as weight. Alot of us run with no air box whatsoever, much less with just the lid off. We're needing you help in that area. I live at 2200 elevation, travel to Dumont frequently, sometimes down to 800ft. Any immediate suggestions concerning these issues?
Considerable gains with what I've applied, but it seems the air box is an issue with your area of testing. What about for us desert dwellers?

 

Additional Carb Mods - Lid-Off or No Airbox

CV carbs have one major inherit problem.
Air flow threw the carb must be straight, uni-directional and constant velocity.

Air entering the carb cannot be swirling or tumbling.
Three problems are generated.

First issue is fact for all carbs - HIGH TURBULENCE CAUSES LOW VELOCITY.
CV carbs are designed to control velocity going into motor. If the air going into the carb
is not controlled, the effectiveness of the carb to control velocity from the carb to the motor is greatly reduced.

Second issue - If air is not controlled, the air passing threw the venturi will have fluctuating negative pressure, causing bad slide control and fuel delivery. Also,
when the turbulent air hits the butterfly the velocity will be lowered more and the end result is reduced total power.

Third issue - Airbox resonance does not occur unless air pressure threw airbox and carb have high inertia. Lid must be on and air controlled. Resonance is caused by spiking the natural frequency of the airbox system. Like ringing the bell.

Now you can understand why I have had more success with running with the lid-on.
I am trying to work around the inherit design of the CV carb.

Future things to try:
Lid-off -
The biggest issue with the air entering with the lid-off, is the lip around the
opening that holds the rubber gasket that the lid rests on. When air hits this lip it automatically causes the air to tumble. I have purchased a airbox so that I can grind off this lip, and see if high rpm performance is improved. Remember my only complaint with lid-off was that at high rpm the motor does not pull. This tumbling air gets to be a major problem from high mid to top rpm.

I have attached a couple of sites that have products to control turbulent air.
These are just for informational and understanding why turbulence hurts power.
I am not recommending these products for the cv carb application.

Example 1
Example 2


No Air Box/Open Filter -
If you live where there is not a water issue, this may be worth trying.
I live where water is everywhere. So I may try this only as a experiment next summer.
This is a high volume system. Velocity control is strictly by the motor/carb.
Turbulence has to be controlled going into the intake tube. That is, because the DS is a large cc machine, trying to control the turbulence just before the carb, as Scaryfast does,
is too late. I would install a horizontal divider where the filter is mounted, going into the intake tube. I think this would control the tumbling air and then as the air travels threw
the tapered intake tube, velocity would greatly increase. The air would be going straight
and thus would past threw the butterfly valve without disruption of the air velocity.
I think this is worth trying. Anyone who tries this, please let us know your results.

My mods to carb are good for all applications, just remember that needle height and main jetting will have to be adjusted accordingly.

Aceisback - Do you want to volunteer!!

 

OMR

Will your inlet tube mod (9" shorter out of sump pump hose) work w/ the TM45 carb? Also planning on using a MODIFIED lid from EHS to cutdown on debris & some moisture in airbox. I have activated A/P on it & it was setup w/ a K&N direct carb mount.
Prior owner only ran on sand, but I want to be able to also run in mts. Couple weeks ago made a couple of stream crossings & so I am alittle leary of running this way.
Also, oil breather line had a filter mounted directly to it at engine fitting pt. Obviously, this was VERY close to water, so I have run it back to snorkel left side between airbox & carb, where it was B4. It was suggested to just run that hose further up frame to a highpt under tank.

Ant suggestions?? (I realize that you haven't done tests w/ this carb etc. , butlooking for input anyway)

KenS