Freeze you must be fast typer

made good reading though and i can see what you said about the flow makes sense. I am an industrial diesel mechanic myself so know the principalls of combustion are straight forward.
i am just thinking out loud here but do you (any of you ) think that it would be posible to mod the stock carb so that it could have the slide pulled open by a cable instead of the cable adjusting the stop position. Then the vacum would no longer be an issue.

Im thinking lock the current cable stop full open and mod the carb top and slide to accept a cable fitting, I will have a look next time i have my carb open to and see if it is possible. Any of you guys who have a stock carb lying in the garage feel free to check this out.

 

I personally love CV carbs. Why, because they are able to match the mixture and throttle opening to the demands of the motor. With Fuel injection, the computer works out air flow and adjusts the fuel delivery to give you the best mixture. The CV carb has the same ability.

The carb will supply fuel according to the demands of the motor. While you ride at constant speed, the CV carb will change opening according to the load on the motor. As the load on the motor change, so does the vacuum and air intake demands and the slider moves up or down to supply the right amount of air and fuel.

With a CV carb you can be putting along at idle and you can crank open the throttle to full, without the carb, over or under supply fuel delivery. This will give you very good acceleration and throttle response. Even at full throttle the slider might be half open at low RPM, thus reducing oversupply of fuel delivery and it makes sure the mixture is almost always correct.

The problem with slider carbs is that they can cause very bad mixtures when you change throttle position, especially cranking it full open at low RPM. I see it on the dyno each time I set up an YFZ. When you crack the throttle open, the fuel mixture goes way wrong. It can go very rich or very lean. The carb has a little pump that forces fuel into the airflow. Force to little in there and its way lean, since the fuel coming up thru the main jet and needle has not matched the demand of the air flowing thru the carb opening. If you squirt too much fuel into the intake the mixture is way rich. This is normally the case. The problem is caused by a massive air flow opening and lots of fuel going into a motor that is not ready for it. The rich or lean conduction will rob power big time. Setting this pump up to give you the right mixture is another story. Once the RPM gets higher the motor can handle the bad mixtures a little better and you don't get such bad effects from the incorrect mixtures. A carb working on a slider is in my opinion a bit crude. Fuel delivery can be very bad when you change throttle position very often. They now add electronics to the slider carbs to get it running a bit better. Throttle position sensors helps the motor to adjust to the fuel delivery changes of the slider carb.

If you modify the CV carb into a cable operated carb, you are going to need the extra fuel delivery when you crank the throttle open.

 

sorry man. I would not have posted it had I known you were eye ballin it.

 

I have a question to those of you that ride a DS and have a buddy with a Predator.

Can you check if the holes in the sliders are the same size and shape between the carb in the DS and the one in the Predator? It’s the same carb, but they might be using a different slider and spring.

If there is a difference it might be worth trying the predator slider to see what it does on the DS? If it works great, you might just be able to buy a predator slider and spring, maybe even the needle to give you that extra bit of kick over the stock DS configuration.

I forgot to add the last way to increase the slider opening. I mentioned this before, but this might be another way to increase airflow into the motor.

Since there is a vacuum, small without a lid and large with the lid in place, between the carb and the air cleaner, it might be possible to get the slider to open a bit larger by removing the breather hose of the carb and connect it to its own little filter. PS, block the hole in the rubber intake. The slider is opened by the vacuum above the slider diaphragm and the normal setup will cause a vacuum under the slider diaphragm by means of the vent being connected to the air intake hose between the carb and air cleaner. The more vacuum above the slider diaphragm the larger it will open. If you take the vacuum underneath the slider away, then the slider should be able to use the same vacuum to open much larger.

Since you are running less vacuum inside the intake, thanks to the open airbox, the less vacuum under the diagram the more the slider will open, since the two vacuums are not competing against each other. With some luck we might be able to get the same slider openings as with stock setup and this means we can use the stock needle even if you are running no lid. Anyone going to test it this weekend? I will try it in my buddies DS tomorrow.

 

I was hopeing no one would spot that with the description,
looks like it will get more expensive now [img]i/expressions/face-icon-small-sad.gif[/img][img]i/expressions/face-icon-small-wink.gif[/img][/quote]
Busmechanic
sorry man. I would not have posted it had I known you were eye ballin it.[/quote]

No problem man its a free market, I new some sharp eyed bargain huntin ds owners would sniff it out

[img]i/expressions/face-icon-small-smile.gif[/img]

 

Freez

Ok i think i understand now (at last) I was thinking that there was sufficiant vacum to try and open the slide all the way even at low rpm/ throttle positions and it would always be pulling against the stop which is controled by the throttle cable. What you are saying is that regardless of me having the throttle pinned open if there is not enough vacum as the rpms are down, the slide will not open to the full position until the rpm and air flow are high enough to give sufficiant vacum. so the vacum actualy controls the slide position not the rider.

thats a clever piece of engeneering and i can see why they are such a bitch to tune

Do i now understand this ? Please correct me if im wrong

 

Yes you have the right idea. The slider takes some time to open. Generally it happens very quickly in the lower gears, but it is slower than the throttle butterfly that works of the throttle cable.

When you are in 5th gear for example and just cruising around 2000 to 3000 RPM and you hit the throttle wide open, the slider might take a few seconds to open to max, since the rpm and airflow is not sufficient to open it fully right from the word go. It will open larger as the RPM picks up and the airflow increase.

I mentioned this before in another post, but think of the slider and spring as a shock absorber.

Airflow into the carb is not a constant. The air actually comes in waves or pulses. These pulses start out slow, then speed up and will slow down again. At some RPMs these pulses can bunch up and actually cause a positive pressure in the intake or even a vacuum. So, try to picture this in your mind, think of the airflow as bumps or whoops. The slider (Shock absorber) is there to try and limit the up and downwards travel and also to dampen the shock movement. The spring tension determines the force (vacuum) needed to push the slider up (compress the shock). The holes in the slider acts like a damper to limit the time taken to open and close. The bigger the holes the quicker it can open and close. The smaller the holes the longer it takes to open and close. Exactly like a shock.
Make the spring to soft or the holes to big, the quicker the slider reacts to throttle changes. But, there is a limit. At lower RPM this slider might start to vibrate since it is able to change very quickly to airflow changes. This is not good for airflow. You need to find a balance between quick reaction time and limit slider vibration.

Like I said, think of it like dialling in your rear suspension. You need to find the right balance to get the bike stable over the whoops.

Hopes this makes sense.

PS. You can actually give this a try. The bike will run without the slider spring. You will get instant throttle opening, but the bike might not accelerate very well. The mixtures will be wrong, but you can still give it a go. It will not damage anything, so see what it does.

 

taking the spring out might cause backfiring through the carb when you try this. the 2000 DSs spring was to light as mine was, upon chopping the throttle the bike would backfire through the carb. What I found out through these fourms is the slide spring wasnt strong enough the slide wasnt closing all the way causing gas to be let in the cylinder causing the back fire. I went to the 2001 spring and the prob. was gone. but one could try it for fun. but Iwould run it to long like that.

 

Yes please don't get me wrong. I was just saying that you can run the DS without the slider spring to prove the point. It should not be done for long and the quad anyways run better with the spring in place. I found this out, when I accidentally forgot to put the spring back after we jetted the carb on the DS. Run like hell when the throttle was wide open, but had flat spots when you where cruising.

 

Been there done that as well, on my way to a 1.5 hr away riding area.