2009 WR450F Newbie Carburetor Questions


I have a recently broke in 2009 WR450F. I’ve done the grey wire mod, throttle stop mod, and replaced the stock tail pipe with a larger diameter Yamaha tail pipe.

The last time I had the bike out it over heated (I was on a steep rocky trail). I’m a newbie, so I’m guessing my crappy technique contributed to the problem, but after doing some reading on this forum I believe I need to make some changes to the carburetor.

To be honest with you I’m not much of a mechanic. What I know about the bike I’ve learned from this forum, my manual, and from talking to a few friends. I’ll apologize in advance if I repeat a question that has already been asked, or if you are just annoyed with my ignorance.

Here is what I think I know, please correct me if I’m wrong. Due to the mods I’ve made, and the elevation at which I ride, I need to re jet the carburetor. I will need to look at the jetting tutorial here on the forum to get an idea of what size jetting I need to use, according to my elevation. I’ll need to purchase a jetting kit, adjustable fuel mixture screw, and a needle kit (JD Needle Kit). I’ll start with following the procedure I found here for “Selecting the Correct Pilot Jet and Setting the Fuel Screw”.

Ok so here’s what I don’t know. While following the procedure for selecting the correct pilot jet and adjusting the fuel screw, do I need to be at the elevation I’ll be riding in? Also, this procedure refers to the settings in the book. My book lists no settings, or a procedure to adjust the fuel screw. In the jetting tutorial, the author recommends a JD needle kit, which I couldn’t find on the JD site, does it exist?. So here is probably the most newb-ish question. I see in the jetting database all different size jets. I took a look at the JD jetting kit for my bike and it doesn’t list various sizes, just that it accommodates elevations from 0 to 12000 feet. I’m assuming it comes with an assortment of sizes, right?

Am I leaving anything out? I would like to thank you in advance for the help. This is a great forum, I’ve learned a lot already from you. Any other help would be appreciated.

Thanks, Hutta

The JD jetting kit is a complete kit. It comes with an assortment of jets that will work over a large elevation/temperature range. And the kit comes with a chart to help you pick the correct jetting for your intended riding area. I made my first voyage to Baja last winter, and used his chart to get the jetting dialed in, all the while living here in Montana!!! To me, that is worth the cost of the kit alone!!!

Along with jetting, I highly recommend a high pressure radiator cap (30psi) to replace the stocker. This will allow much higher temperatures before boiling over. Your still using the catch tank, right?


You can also install a cooling fan to help when you are moving so slow. I bought a computer fan from Radio Shack for about $18. It is the perfect size. I mounted it on the upper back side of the right radiator, just used zip ties threaded through the radiator fins, only needed two on the top and one on the bottom. I'm just using a toggle switch, but a temp switch would be better.

Hi guys, thanks for the responses.

It sounds like the JD kit is the way to go then, the chart would be very useful. How about the needle kit, ever heard of such a thing? I will start looking for a new radiator cap as well. Are there any disadvantages to going with the higher rated cap? Seems like a good thing to me, if it keeps your coolant from dumping on the ground. I am using the catch tank, but in the heat of the moment I didn't even think to look at it when it happened. By the time it occurred to me to look, after 10 or 15 minutes of letting the bike cool, it was empty. So I'm assuming it was full, and dumped the excess on the ground? How was Baja, any problems with your bike? I'm hoping to get familiar enough with my bike to take a long trip like that one of these days, sounds like a lot of fun!

I've also been thinking about installing a radiator fan. I was eye balling it last night, and was wondering if I could get one to fit. It looks pretty tight between the tank and radiator. Do you use the stock tank? I'm using the stock tank for now, but I'm considering moving up in size. I'm guessing the clearance would be pretty close to the same for most of the after market tanks?

Thanks again guys, I appreciate your help.


I have a stock tank and an Acerbis 3.3 gallon. I can't remember if I've had the stock one on since adding the fan, but I'm pretty sure it fits too. The fan is only about 1" thick and about the size of a slice of white bread (5x5" I guess).

You don't need a kit. You need a $6 main jet, which is a 165 for your bike if you live anywhere from sea level to 2,000 feet. that's plenty rich for slow hot tight trail riding.

Ok great, that is the tank I was looking at. I'll have to head to radio shack and check out some fans. Are they pretty durable? I'd worry about them failing if they get dusty or dirty. At that price though I guess it's not too much of an issue.

You think a main jet would do the trick? I think the elevation is about 2000 feet where I ride, but we climbed maybe another 1000 feet or so I think. Are you familiar with Harris Park in Milton Freewater, OR? I'm not exactly sure what the elevation is there, but that is where I was when she over heated.

Thanks guys.

A 162 is a good starting point, them.

There is no such thing as good jetting for 0-12000 feet.

You change the main jet for every 2,000 feet or 25 degrees. That is super impractical for most people, so you try to get it close, and these bikes are very forgiving of incorrect jetting.

Thanks for all your help guys. I'll give it a try!

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