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yz250 smoking - jetting??


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I have a 03yz250 which has ran great since i got it in the spring, since i got it, it has progressively been smoking alot more and the spray of 2 stoke oil on my fender has gotten bigger. I just put a piston and rings in it thinking it was that, but it smokes just as much. Im thinking it might have to do with the jetting. IT has a fmf sst wit ha turbine core 2 silencer, and the main jet size is 178, i run it at a 40:1 mixing ratio, any suggestions to keep the smoke down? ive been starting to feel like a dick when i leave people in a cloud of smoke at the track

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Clutch side crank seal is bad, so transmission oil gets into the cylinder and causes lots of spooge despite good jetting. You can replace both clutch and flywheel side seals without splitting the bottom end. Drill a small hole in the rubber-covered bronze seal, screw in a small screw, pull on the screw to remove the seal.

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thanks, that actually makes a lot of since because when i went to change my tranny oil last week there was almost no oil in it and the oil that was in it was completely black. Im having trouble picturing where u want me to drill the hole though, and once i get it out, how do i get a new one back in?

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They mean when you are removing the old seal, you may have to drill into the outside of the seal itself with a small bit, put a screw in it and use that to work it out. This is a very delicate process as the shiny crank bearings are just behind the seal so only need to just get through the metal seal wall (1/16th inch?). One trick is to use built up duct tape on the drill bit to act as a stop and possibly also on the screw if you wanna be extra careful.

I didn't even have to drill the right side crank oil seal on a 1997 yz250. Just used a flat blade screwdrive to gently work it out. Used the old seal and a socket to drive the new one in.

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The ONLY way to get that seal out without splitting the cases is to drill a hole like everyone else is saying. There is no way to grab the seal and pull it out without doing so.

I used drywall screws because of the large head and large threads, they worked perfectly. By the way you can pull all you want but unless your super man that seal aint coming out. You need a slide hammer or improvise to make one, it's the only way.

I did both clutch side and flywheel side seals 3 weeks ago.

Also, you need to have a flywheel puller to do the flywheel side.

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At first I thought it would be easy, but it was alot of work and took about an hour and a half.

Remove the pipe, then remove the powervalve cover and disconnect the power valve cover. Remove the rear brake pedal and drain the coolant, disconnect the water pump hose. Remove all perimiter clutch case bolts, including the one on the water pump edge and the top and I believe the bottom clutch cover bolts. You do not have to remove the clutch cover, it can stay with the clutch case.

You may have to lightly tap the clutch case with a rubber hammer to loosen it, but tap LIGHTLY it shouldn't be too hard. Pull it straight off as there is the power valve shaft and water pump shaft that come out of their respected bearings. Using a piece of aluminum that is flat, wedge it inbetween the gear on the basket and the primary gear sprocket and loosen the 14mm nut that holds the primary drive gear in place.

Remove the pressure plate bolts for the clutch then pressure plate, then friction/steel discs.

Using a flat headed screw driver and a hammer, flaten the lock washer tabs around the clutch hub nut. Using a clutch holding tool attach to the inner hub and have it rest on the bottom of the right peg so that the hub will not move when removing the bolt. Use a breaker bar about 2 feet long and a deep 29mm socket, remove the clutch nut.

Pull out the inner hub, washers, bushings and double roller bearing along with the basket.

Remove the primary drive gear and water pump/power valve drive gear from the shaft to expose the seal with retaining tabs. Remove the tabs.

Use the trick I mentioned above to remove the seal.

Remember to use loctite (blue) on the bolts for the seal retaining tabs, if they vibrate out cause you didn't use loctite your clutch side is toast.

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