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How To Adjust The Needle in Your Motorcycle or ATV Carburetor

How To Adjust The Needle in Your Motorcycle or ATV Carburetor

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.

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31 thoughts on “How To Adjust The Needle in Your Motorcycle or ATV Carburetor

  1. I am using 50:1 on trails. my spark plugs are getting ruined all the time. They told me to move the pin on the needle so less oil gets to the top end. I dont know if I move the clip down or up. Thank you.

  2. Ok so i have a four wheeler and the carburetor needle is not pulling up or down. At this point i think its my throttle. What do u think is wrong with it? Any suggestion will help

  3. Great video. Would using 2 year old oil/fuel mix contribute to fouling plugs? I have a 1999 Husky WR125 and it was fouling plugs all day today. It was over 90 degrees with high humidity and the fuel was old.  I was thinking of adjusting the needle, cleaning the air filter and replacing the fuel.

  4. My yfz 450 is back firing mid to full throttle on deceleration it's bored to a 501 I'm running a 180 main and 48 pilot 2nd clip from the top and 3 turns out why any idea what I should to to get rid of that back fire I have been told it's to rish but also been to its to lean any ideas thanks

  5. my yfz has gutted exhaust I feel like it not running right. a buddy of my dads said that I could running with too much air,I blew my head gasket,so if anybody know anything reply to me please. thank you

  6. My 2005 YZ450F is backfiring. it idles fine, so the pilot jet is correct. But once i open the throttle and let it off the backfiring starts. Should i move the needle richer or leaner?. Thanks in advance. 😊

  7. Question I have a yz426f and in mid throttle it sputters. It this caused by to rich or do I gotta move a clip to lean it?

  8. I have a flat cr like this and I have that electric solenoid that's like a main jet shut off or something and I think it quite do you have any videos on that don't want to pull it out till I know what I'm doing it's got those tamper-proof Torx keys and I wanna know what I'm getting into before I pull it off it's just a swap a new one and let me know because I think it quit whenever I rev the bike without the choke on it just dies out clean carburetor everything else works good Jets and you don't write everything worked great till I think the solenoid just quit.

  9. Hi I have a question I just rebuilt my carb and when I’m running I’m ok but when I try to give it gas it try’s to die only when I lean the gas in does it take off when it’s ideling it’s ok but why I pump the gas it try’s to die help me please 88 warrior 350

  10. if someone is here to know why their bike eats too much fuel then you need to see if this needle has scratches on it . i saw my needle with scratches on one side, so i got it that the fuel goes more then air into the carburetor process because the needle had scratches on the tip

  11. Hey partner great video, I've got popping on deceleration on my 450 and
    was told the hot start might not be closing all the way, I never use it
    or need it can I just pull that off and plag that hole with a bolt of
    some sort? Thank you