Dirt Rider Magazine

2strokevirgin

i have a 1998 kx250 k5 kawasaki you know the deal. anyways i need to know what premix ratios i need to use for cruising my bike at long high speeds like for travel on roads at least a good 15 miles at 50mph. idk how many rpms. its got a fresh rebuild on top and a fmf gold pipe series with a fmf shorty pipe.

will riding this bike like this affect it even if i maintain it????

all answers appreciated.

BleedMarshall

A great ratio is 32:1, and then adjust from there if need be, but that should get you going fine. As for what speeds/distances cause more wear and tear...both. The harder and faster you ride, and thus the longer you ride in overall hours, will wear a bike out faster. Racers wear a top end, for example, far quicker than a weekend warrior would due to more hours on the bike. However, proper maintenance is the key to the longevity of any engine no matter how you use it. Keep it maintained and you will be fine for at least 100 hours.

2strokevirgin

awesome thank you very much !

NZrider

IMO the best thing you can do to make sustained high speed running safe is richen the jetting in the area of sustained use. so more than likely you'll be cruising with quite alot of throttle (maybe 75%) so you'll need to richen the needle or if possible get a needle with a steeper taper so it gets richer the more you throttle on.

PaulB14

When I used to race in the desert I would richen it by installing a larger main jet. In addition to running a bit richer I would also reach down and occasionally pull the choke lever up while running wide open for longer than a mile at a time. And yes, it is harder on the top end to run wide open for long distances. But since you are only running around 50 mph you can ease the throttle on and off as you travel and shouldn't have to run wide open much. I agree with NZrider that the 32:1 mixture should work fine. But having said that, I would race with a 40:1 to 50:1 mixture (depending on the temperature) during a race because it would help to keep the engine running cooler.

2strokevirgin

awesome but what im confused on now NZ and paul is how do i get a different jet ??

BleedMarshall

What do you mean "how"? I assume you mean how to buy a new one. Several places sell differing jets, both pilot and main, so you can change them out. Try RockyMountainATV/MC, Motosport, and CheapCycleParts. All are .com sites.

PaulB14

To know which jet you should get, first remove the main jet that is in there to see what size it is (the size is stamped on the jet body). I always have extra jets on hand, usually 1 size bigger and 2 sizes smaller, because I have a lot of elevation changes for different rides or races. If you are going to be staying at only 1 elevation then just 1 size bigger may be all you need.

2strokevirgin

well like how do i get em out? ive cleaned them before but i never new they ere removable

PaulB14

The main jet can be accessed through the bottom of the carburetor. Remove the bowl. The main jet is the 6mm hex head brass screw with the hole in the center. I'll post a couple pictures from my bike here:

In the above picture, the main jet is noted by the arrow. The pilot jet is also visible here, it is the slotted brass screw just to the left of the main jet, sunk in the carburetor. I would not change your pilot jet since it only controls the very bottom of the throttle. With my carburetor I can also get to the main and pilot jets simply by removing the drain plug on the bottom of the bowl (next picture):

PaulB14

Your carburetor may look different than mine but they are all pretty similar. If you are going to start working on your bike I would highly recommend that you obtain a service manual.

2strokevirgin

awesome! and yeah a manual would help lol.

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