Most of what i hear is tuning one carb is easier and, faster. I would say it would be equally as easy if they came up with a different carb design for the duals. Make something that you could changes the jetting and, needles while they are still in the bike. These carb designs have been around forever. Only place i really see progress is lacking.

I'm no carb engineer but, why not design a carb that can be adjusted by (for instance) sliding out a jet from the side and, sliding in a new one. Have it so they are quick change or, even done by a easy to get to dial for "all" the carb settings!

I guess the easiest way is just plain old fuel injection with a small computer for control. Every car has one now and, i'm sure it couldn't be to much $ in R&D. They'd make us pay for it though!!!

 

Yes it is. We're having a hard time finding a dyno.[img]i/expressions/face-icon-small-disgusted.gif[/img] You would think in that in the northern half of LA county that wouln't be a problem.
I'm glad to hear you got yours running good, I know it was giving you fits.

 

try Luttig Performance regarding the Dyno. They may have one or know where one is.

 

Freez you get too deep for me, but you have a ton of great info, i prefer to take it to the hill, and i will put my single Lectron top end against any duel set up....this crab rips and i havent really fine tuned it[img]i/expressions/face-icon-small-happy.gif[/img]

 

Just one more here from Duncan.

"First on Duncan’s list of mods is the DRI 740cc National kit. This includes stainless exhaust, head porting, valve job, HD valves, big-bore sleeve (installed), high-compression piston and cam. Machining the cases is required, too.

Next up is the single Edelbrock carb, to replace the stock dual carbs, which can be a headache to jet. Why Yamaha went with dual carbs on the Raptor is a mystery to Duncan. “They don’t carburet as well and are more expensive than a single carb. Weird,” he says. "
rnuts





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Here is the big problem with the comparison between the single and double carb theory.

Have anyone ever thought that the problem with the dual setup might not be the carbs themselves. Maybe the combination of intake and breather pipes and the design of the airbox is the problem. Changing to a snuggle carb gets rid of the pipe work and the airbox and people rave about the increase in power.

MAYBE if you get rid of the pipe work on the dual carbs you might get the same power increase, maybe more than a single carb. The sixsixt adaptor gets rid of the airbox and people claim a very good power increase. He used the same old duel carbs. Now I am running the L&N adaptor and I have nothing if the pipes and the airbox on the carbs. I am not claiming the one is better than the other, but lots of people, including myself had problems with low RPM stutter when I run the open lid. I am not sure if that stutter is still there with the sixsixt kit. The stutter is caused by the intake pipes between the carb and the airbox. These pipes might be tuned to operate at a certain RPM, but removing the lid off the airbox, put them out of tune. This is why they cause negative pressure waves inside the pipe and this in turn messes with the slider on the CV carbs.

So maybe the pipes are to blame for the lower RPM output. I am running the spark pipe, with the L&A adaptor and a dynojet kit. This gave me a 49.5HP run with stock tires. This HP was also achieved with the exhaust piped partly blocked to measure the air to fuel ratio. Getting close to 50HP on a stock motor and using the dual carbs is nothing bad. I am going to run this bike next weekend on the dyno with slick tires and no blockage on the exhaust and I believe I will break more than 50HP. This is all with stock carbs.

What is a single carb going to do more for me?

When you change it to a 686 or bigger, then yes, you will have to rethink the carbs.

Now to the single carb. There is no off the shelf adaptor than work perfectly for the single carbs. Sixsixt said he had to modify the intake he got to make it flow better.

The raptor has 3 intake ports, with a big blockage between the 1 and the last two ports. The ports also curve a bit .Adding a adaptor that splits the air into two, then passes into another port area where it is split into 3 is even worse.

The last two ports have a single feed. Meaning that if you split the air the 1st time from the single carb, you have to make sure the flow into the duel port feed will be higher that the "single" port feed. If the split or port side on the adaptor is 50/50 you are feeding 50% into a single port, which is much smaller that the intake and can become a flow restrictor and 50% for the other two ports, where they might be getting the wrong mixture and flow. The dual carbs are set up differently, and feeding a 50.50 split might cause mixture problems. You might never see it, because one side of the gas might be to rich and the other side to lean. This might cause bad burn and loss of power. Some people also make their own adaptors, without any idea what it does to the air flow.

These port and feeds need to be designed by experts, It’s not just a port. Its way more than that. Get it wrong and say bye bye to power.

 

Freez I have to disagree with this:

The last two ports have a single feed. Meaning that if you split the air the 1st time from the single carb, you have to make sure the flow into the duel port feed will be higher that the "single" port feed. If the split or port side on the adaptor is 50/50 you are feeding 50% into a single port, which is much smaller that the intake and can become a flow restrictor and 50% for the other two ports, where they might be getting the wrong mixture and flow. The dual carbs are set up differently, and feeding a 50.50 split might cause mixture problems. You might never see it, because one side of the gas might be to rich and the other side to lean. This might cause bad burn and loss of power. Some people also make their own adaptors, without any idea what it does to the air flow.

1) There is a crossover port in the head from the single valve port to the dual valve port.

2) The air would not be split 50/50. You would need a runner going almost all the way up to the needle to do that and have no crossover port in the head. The velocity may increase on the dual side a little more tho due to the two valves demanding more air then the single port.

3) The A/F mixture is made at the carb, the path it takes to the combustion chamber is not going to change that. The dual carb set up would have that problem tho. When jetting dual carbs how do you know one isn't a little rich and the other a little lean? And then trying to ballance them both to be the same at all throttle positions is an even bigger problem. That's what causes more stumbling problems with the duals then the intake tubes.

A dual set up may produce a little more power if tuned perfectly but a single can be tuned way easier and as you know from working on the dyno the tuning can make a big difference. The Lectron carb is also more effective at atomizing the fuel which gives it an edge over other dual set ups.

We're not sure that this is going to be a better set up then dual FCRs but unless someone tries it you'll never know. It would be nice to dyno each set up (single, FCRs and stock modded) on the same bike and see.

 

Yes that would be the way to go, If you got the time and the carbs setup, that would be very interesting to see.

I dont know about pulling off single carbs and putting on duals for the DS but I do know Bigbaja has a single carb on his DS and that thing rips. Also, talk to Mario, he is running single carbs as the last time I seen him and his DS is the fastest I have seen so far but Bigbaja maybe very close to him now.

I do like my dual FCR's and from what info I got from Edlebrock as well I wont be using them on a drag bike.

 

Answer to sixsixt's response

1) There is a crossover port in the head from the single valve port to the dual valve port.

That is correct, but the restriction of the flow is before the crossover point. The port size of the single valve at the head is smaller than the two valve port size. So you can have as big a crossover as you like, the two ports will need more air. If you have a 50/50 split you are feeding a small port with a larger intake and on the other side you are feeding two valves with the same size intake as the single port. Now I know you are going to say that its the same set-up with the dual carbs, as they are the same size, but there is a difference. With a single carb all the ports suck air thru the same passage (single carb). With a 50/50 split manifold, the speed of the incoming air will cause the flow to split into two parts. If the split is right in the middle and 50/50, that’s what the air will do. 50/50 it will split due to the speed of the flow. Remember that the air is flowing at extremely high speed and acts more like a liquid. Fast flowing “liquid” does not turn that easy. You can prove this very easily. Take a flat peace of metal and place it inline with the exhaust flow. Start turning it into the flow and feel the pressure it starts creating. This plate test also gives the air other places to go to when it changes direction, but inside a port it can only go in one direction, DOWN the restrictive port. When the valves open, the vacuum starts out small and the single port is not a restriction. When the valves are fully open, the small port might be a restriction and cause the high speed air, that cannot turn so easy, to cramp up, while on the other side of the head it might have a lower pressure. The cramped air will try to flow over to the low pressure side, but in order to do so it has to slow down, stop dead and turn around. This might cause very strange or reverse flow. On the DS, you do not have this problem, as it has two intake ports of the same size. The raptor head is just not made for a single carb. If it was it either had to use two intake port with the same size, or have a single port like the YFZ to breath from the carb. Splitting air is bad for performance

With dual carbs, you do not have a single intake and splitting of the air. Since the two carbs each have their own intake, there is no "accidental" flow into the single port intake. Remember that the restriction is before the existing crossover in the head. The single intake port might suck less air than the dual port, but the flow of air will be directed directly into the port and no overflow or bunched up air will take place.

2) The air would not be split 50/50. You would need a runner going almost all the way up to the needle to do that and have no crossover port in the head. The velocity may increase on the dual side a little more tho due to the two valves demanding more air then the single port.

You are right about the velocity difference between the ports, but as I explained, air moves at extremely high speeds inside the head. It’s like fast flowing water and it takes time for it to change direction. If the air is flowing into the wrong passage and it cannot escape, its not that easy to just flow over to the other port. The sheer speed and the air behind it causes a restriction and cramping the air into a small port where it needs time to escape.

3) The A/F mixture is made at the carb, the path it takes to the combustion chamber is not going to change that. The dual carb set up would have that problem tho. When jetting dual carbs how do you know one isn't a little rich and the other a little lean? And then trying to ballance them both to be the same at all throttle positions is an even bigger problem. That's what causes more stumbling problems with the duals then the intake tubes.

I agree with you about the mixture, but as the air moves along the intake and it splits up or changes direction, the heavier fuel droplets will not be able to change direction at the same speed as the thinner air. This might cause the fuel to drop out of the air and cause lean conditions. The air between the ports might end up with different amounts of fuel as it enters the cylinder, even thought they started out the same.

The more turns you add to the intake port, the more you will change the time for the fuel and air to pass thru the port. Each time you change the air direction you might slow it down or speed it up. On an aircraft wing the curve on top of the wing will cause the air over the wing to speed up and the air below it, will keep its speed. If the bend is to tight, the air will slow down due to drag and cause turbulence. If this happens inside a port, it causes bad flow. Now if you go back to the wing theory, as the valves open the air will not start flowing thru the ports at the same time. This is because none of the intakes are the same length and the turns can change the speed also.

Duel carbs have a much more direct flow into the head. Less turbulence and the length of the ports are also more similar and the air speed is more constant, as there is less turns.

Again, this is all airflow theory and like you said, we would need to test this on a dyno to prove the outcome.

PS. Here is a tip for the duel carbs. Remove the breather pipes on the stock carbs and install a breather filter to each one. It helps bottom end power and on the dyno will give about 1 to 3 HP more. It does not add to top end power.

I know some people with disagree, but lets keep this of later. If you understand why I say this, you will get a step closer at producing more HP with the stock carbs.

 

Freez you use to many ifs and mights in your argument. Look at the picture of the intake on my page. You'll see that the carb sits off to one side, it does not split 50/50.

Fuel droplets in the mixture that would get sepperated from the air would not burn very well if at all, the fuel needs to be atomized to burn well. In fact gas in a liquid state does not burn at all. If you have a carb that produces droplets and doesn't atomize the fuel you need to find a different carb.

Quote Freez "You might never see it, because one side of the gas might be to rich and the other side to lean. This might cause bad burn and loss of power.

So please tell me how you know that one carb isn't a little rich and the other a little lean with a dual setup on the raptor.please [img]i/expressions/face-icon-small-smile.gif[/img]

Another quote "When the valves are fully open, the small port might be a restriction and cause the high speed air, that cannot turn so easy, to cramp up, while on the other side of the head it might have a lower pressure. The cramped air will try to flow over to the low pressure side, but in order to do so it has to slow down, stop dead and turn around. This might cause very strange or reverse flow."

Not with the crossover port there.