I didn't create this, so the credit goes to Freez!
"It’s my 1st post, so I hope you guys find this useful. I have spent years messing about with the carbs on the 660 raptors, and I picked up a few tricks in the process. The basics on how to set up the carbs have been posted, so I am not going to explain more on that. What I will tell you is how to set up the stock carbs to release some hidden HP, and make that rappy go like it has never gone before.
This post is a modified version of my post on another forum, so some of you might have seen this before.
So, let's get started.
You need to remove the front plastics, and the fuel tank. This should be a 10 minute job, and a great explanation can be found in the stick section of this forum.
Before you start you need to decide if you are going to run with the airbox lid on, or off. The carb settings are different for both options.
If you are going to run with the stock air cleaner or an air cleaner without the billet adaptor, you need to run with the lid on. It keeps the air cleaner in place.
Now if you are wondering what the best setup is for running with the airbox lid on, here is what you need to do. Remove that stupid rubber snorkel, and throw it away. No matter how you modify it, it drops power output, so just get rid of it. I have proven this on like 50 raptors, using my own dyno, so just take my word for it. Next, remove the lid and you will find there is two “tubes” underneath. Cut all the plastic “tubes” open, so you end up with no tunes at all.
If you are worried about water or mud getting into the airbox stop here.
If not, and you need the lid to hold the stock air cleaner in place, you can cut about 3 to 4, 2 “ holes into the lid to get air in there. Try and space the holes evenly to create even airflow around the air cleaner.
Then, if you want to do this correctly, get yourself a jet kit. I prefer the Dynojet kits and I have proven it on my dyno that the Dynojet needles work best with the no airbox lid setup. The GYT-R and stock needle either supply too much or too little fuel.
Again, have a look at the carb sticky to see how to install the jet kit.
Now, this is something you can try and experiment with, but my dyno seems to indicate the following works well. If you run with the lid on, use the Dynojet slider springs, but if you run without the lid, use the stock slide springs.
Install the Dynojet needles as per the kit instructions. You might want to experiment with the clip positions, Maybe 1 clip higher or lower is better, but the instructions are generally quite close.
Next, drain the fuel from the carbs and remove them. I did not take the throttle cable out. It is possible to work with the cables attached. Below is a picture of the carbs upside down. You will notice a clear tube on the one carb. It will be used for checking the fuel level at a later stage. You need to move the clear tube from the one to the other carb to check both float/fuel levels. Keep in mind that they will only be used when the carbs are mounted back on the motor.
Remove the float bowl. You have 4 screws on each bowl. Take note, these screws are very soft and strip very easy. Use a nice big screwdriver that fits the screw perfectly. To small and they will strip. A good tip is to support the carbs, insert the screw driver, and with a hammer, give the screw driver 2 to 3 nice firm taps. This usually helps the screws to loosen up, before you start removing them. Another good tip is to get new steel screws if you can, and throw those damn stock screws away. Also take special care when you tighten them later. The picture next to it shows different coloured arrows.
The red arrows are for the fuel mixture. Turn them in until they are seated. NOT TO TIGHT. Then turn them out 3 times. (I used the Dynojet stage 2 kit settings. It might be different for other jets)
For a modified lid, get yourself size 25 pilot jets, and run them around 3 turns out. If you run without the lid, I found that the 27.5 pilot jets are required, also using 3. to 3.5 turns out.
The Blue arrows point to the floats. More later.
The green arrows are pointing at the main jets. More later.
The yellow arrows are the air or pilot jets.
Install the main jet as per the Dynojet instructions. Again, look at the carb sticky to see how this is done.
Now to check the float levels. THIS IS THE KEY TO RELEASING THE FULL POTENSIAL OF THE RAPTOR POWER.
To give you a base point you can use the method the Yamaha manual recommends. With the carbs hanging at 90 degrees with the openings that connects to the motor facing down. Move the carbs between the 90 degree position and upright and look at what the floats are doing. When the carbs are the right way up, the floats are hanging fully opened. When you start turning the carbs to face 90 degrees down, you will notice the floats move and suddenly pause. It will pause for a little while, but if you keep turning it to make the openings face down to the ground, they will move again. You need to find where they pause, and keep it there. This position is where the floats touch the needle valve pin, but not compress the needle valve spring. Measure between the split (place where the float bowl and carb comes together) and the of the float shoulder. It should measure around 14 to 16 mm. The image is showing you how to hold the carb in the right position. It shows 13mm, in the picture, so try make them slightly larger.
The floats on ALL stock raptors are out, and needs to be adjusted. It is set to low at the factory. If you need to adjust the level, you need to take the floats off. There is one screw that holds it in place. Remove it and off comes the floats. A small little needle valve will be dangling on the float. Take care of it. The picture below shows it apart.
With the floats off, you will notice a small little metal thingy at the back of the floats called a tang. You need to bend it to get the right float level. Bending it down towards the bottom of the float will lift the float level. Bending it towards the top of the floats will lower the float level. Generally you can bend it lower, then put it back in the carb, check if it is measure14 to 16mm. If not start the process again, till you get it more or less correct. Do small amounts of bending at a time. The tang is very sensitive.
Once you are done, you might run into a small problem. The floats might not open fully, and you might find that the motor sucks the carbs dry. With the float bowls on, turn the carbs upright, and hold them in the normal mounting position. Now blow into the pipe that connects to the fuel tank. You should be able to blow air easily through the fuel pipe. If you turn the carbs back to the 90 degree angle, it should stop flowing air. Also try holding one float closed at a time and do the same process, making sure both carbs flow air when you blow on the fuel hose. Don’t press to hard, or you might have to readjust that levels again. If it does not flow air, or it is hard to blow thru the fuel pipe, you have a problem. You need to mod the floats. It should flow easy, but keep in mind there is only a small little hole. If you are not sure how well it should flow, take one float off, and remove the needle valve. Now close the remaining float by turning the carb upside down and blow on the fuel pipe. It should now flow air easy and you can get a feeling for how it flows.
The below picture shows the float level mod. Take a small little file or sharp knife and file/cut down the little plastic stopper at the back of the float. DON’T shorten it, just take a 45 degree angle off it. Take little chunks of at a time. Take note it should look like the float below. The screwdriver is pointing at the little stopper.
After this mod it should open real easy and you should have no problem blowing air thru the fuel intake pipe when the carbs are the right way up.
Try not to cut them too far, so that the floats lie on the bottom of the float bowl. Remember do this very carefully, and little bits at a time.
When this is done and the floats are set correctly, put the carbs back together. Take note not to tighten the screws to much. When the carbs are all back together and you need to putt them back. I found that I struggled with the rubber intakes on the head. To prevent it from struggling to go back in, make sure the clamp screws are loose all the way. Then dip your finger in same fuel and rub it inside the intake, See below. With the fuel still wet, the carbs will slide in real easy.
Now to check the float with the carbs in place. You don’t have to tighten the clamps on the rubber intakes to check the float levels. Do that once the level is correct.
1st put the fuel tank back, again don’t worry about tightening it up. Connect the fuel hose from the carbs to the fuel tank and open the little tap. The fuel should now flow into the carbs. Check for leaks. If none, you check the floats using a clear tube. The size of the clear tube must just fit the little drain hole on the bottom of the carb. I showed you before where this pipe connects. The picture below shows you the clear pipe and the screwdriver is pointing to a small screw on the bottom. Point the clear tube up and above the section where the carb and float bowl joins. Open it up and you should see fuel run into the pipe.
When the fuel stops flowing, tap the pipe a little to make sure there is no air bubbles trapped inside it. Push the pipe against the carb and the fuel level should be EXACTLY 3mm between the carb and the float bowl. Check both carbs. You will have to move the clear tube and go to both side of the bike to check the two carbs. Don't try checking it from the same side. See picture. PS. my finger is not pointing at the fuel level, it is only holding the pipe in place. The RED arrow is the place you need to use to check the float level against.
If it is not exactly at 3mm, close the fuel supply, drain the carbs and start again. I cannot stress enough how important it is to get it exactly at 3mm. 4 or 2mm is not going to cut it. Keep adjusting the float tang, till you get this right. Less than a 1mm adjustment is mostly what you need to get this right.
Then, if you like to go a step further, and release even more hidden horsepower. Remove the carbs, and feel inside those rubber intakes. You will feel that they are not matched to the intake ports. Get a Dremel tool, with a 80 grid sanding drum, and open those rubber boots up, so that they match the intake ports perfectly. Do this in stages, and with caution, and take your time, I you mess this up you will need new intake boots. Once done, clean them very well with fuel, and install them back where they came from, followed by the carbs.
Now when you are happy with the results, tighten up all the clamps, put it all back together and make sure there is no bolts and nuts left.
One last thing. You will gain about 10% more power with this mod, and about 15 to 20% more if you remove the lid in the process, and run a high flow air cleaner. Throttle response will be much better, and you will feel the extra power. It also helps the bike to hold its power peak further into the RPM range, and you can stay in a gear longer, before having to select the next one.
I have done this to about 50 different 660’s, and they all show good power gains. A stock raptor picks up 2 to 3 HP from the float level mod and intake boot matching alone. It works even better when you add a better exhaust and air cleaner to complement this mod.
Try this, and you will not believe the difference it makes.
It will wake up that rappy of yours, and give it a whole new level of power."
