In this video we’ll explain the function of
the needle in your carburetor and also the proper way to adjust it. This process will slightly vary for each carburetor, so always refer to your service manual for proper procedures and specifications. In most cases you can adjust this with the carb left on the machine. Keep in mind some machines will require different steps than what’s shown in this video, so be sure to refer to your service manual. Today we’ll be using a Keihin FCR carburetor which is found on most modern day four strokes that aren’t fuel injected, but we’ll also
show how to remove the needle from a Keihin PWK carburetor which is found on popular two stroke applications. We’re just going to need our service manual and a few standard tools to complete this job. The needle primarily regulates fuel flow between 1/8 and 3/4 throttle. It’s essentially a tapered rod that’s connected to the throttle slide. As the slide opens the needle is pulled upward, and since it’s tapered, as it rises with the slide the opening in the needle jet gradually
increases, allowing more and more fuel to flow through. The needle has a clip with different slot positions that allows it to be lowered and raised in relation to the carb slide. This gives an overall leaner or richer mixture. Raising the clip up a notch drops the needle down causing a leaner mixture. Lowering the clip raises the needle causing
a richer condition. Some regulated street bikes have fixed needles and therefore can not be adjusted, but most off-road machines will allow this adjustment. The first thing you need to do is get access to the top of the carburetor. We do that by first removing the seat from the machine. After that we can remove the tank. Once that’s out of the way we’re going to blow off all the dust and dirt to prevent anything from dropping into the carburetor while we have it open. On this bike it’s necessary to remove both top motor mounts to access the top of the carburetor. So we’ll go ahead and do that. There are five bolts that hold these in. Once those are out we can pull those out of the way. Doing that gives us the room we need to get to the carburetor. Next, we’ll take a hex key wrench and remove the two bolts holding the valve lever housing cover on. When both those bolts are out just go ahead and remove that top cover. Under that you’ll see the top of the slide and your throttle shaft assembly. In the top of the slide is a plug which we’re going to remove with the hex key wrench. Go ahead and break that free, and then back that plug out. Attached to that plug is a small spring and
small brass collar. Make sure not to lose any of these parts. We’ll need a small pair of needle nose pliers to reach down and pull the needle from the carburetor. To get the needle out of the PWK carburetor, simply remove the two bolts holding the throttle valve housing assembly cover on. Once those are out that cover will pop off. Go ahead and gently pull the slide assembly up and out of the carburetor. You can now see the needle coming out of the bottom of the slide. Now the spring needs to be compressed in order to create enough slack to slide the cable down and out of the holder and remove it from the slide assembly. Next, we need to remove the holder from the inside of the slide. We’re using a socket to do this. Once that holder has been removed the needle should just come right out of the top of the slide. Now we can just start making adjustments. With the needle out you can see the small clip used to adjust the needle position. Now is a good time to refer to your service
manual to see what the stock setting is for the clip position. Usually it’s somewhere in the middle, and as you can see this one’s sitting in the third slot from the top. To remove the clip from the needle simply position the open end of the clip face down on a hard surface, and using a little downward pressure the clip will pop right off. To put it back on place the clip into the desired groove on the needle, and again using a hard surface, use downward pressure to seat the clip into the groove. After that, drop the needle back down into the slide of the carburetor and reinstall that top retainer plug. Go ahead and snug that plug down. Now we can reinstall the valve lever housing cover and the two Allen head bolts that hold that on. We’re going to want to tighten both these bolts down as well. After that, we can reinstall the top motor mount, the fuel tank, and finally the seat. Rocky Mountain carries a huge variety of OEM and aftermarket carburetor parts for your motorcycle, ATV, and side by side. Be sure to check out our website for a complete list of parts and accessories for your machine. Thanks for watching.