bought a used 03 yz450f, anything i should check?

so i recently bought my boss' old 03 yz450f. this is my first dirtbike (have street/track bike), and as far as maintenance for dirtbikes goes, i have no idea what to to check on. whats some routine stuff to check for? how much should the chain sag for instance?

on its first 30+minute run yesterday, the pipe was popping alot which im guessing means its running rich cus the pipe was popping the extra fuel, is that right?

also, what are some essential stuff i should buy for it?. its basically stock besides being rejetted for the desert and a pipe. im guessin the onyl thing it will be used for is desert riding and a few times at the track.

ok ok last question, should i take the dirt msf? i took the street one a few years back and i found it geared toward someone whos never ridden a motorcycle in their life.

anyways, here she is, sporting a 50 tooth in the back (pre-installed), as if it wouldnt try to rip my arms off with the stocker :banghead:


The first thing to do would be to check the valve clearances, just to get a base benchmark of where they are. Don't be surprised if they don't need to be adjusted.

If the popping in the exhaust is on decel, it's due either to a lean idle condition, or an air leak in the exhaust. Usually the leak will be at the midpipe joint, or the head. Pipes like the FMF that have no clamp at the midpipe will sometimes do this no matter what you do, at least to some extent. Check the exhaust first, before you try to "cover up" the problem by making the idle richer than it needs to be. If the exhaust is OK, set up the idle so that the bike runs right, and if it still pops some, don't worry about it.

Maintenance is pretty much confined to keeping it lubed and keeping the air filter clean. Change the oil every 10 hours or less and clean the filter or replace it (depending on the filter type) each time. An occasional check on the valves, and they are otherwise "turn-key". The chain adjustment is spec'ed at 1 5/8 - 1 3/4" at the rear chain slider bolt on top of the swing arm.

The two things that "have to" be modified on a stone-stock '03 are the grabby, chattering clutch, and the complete lack of rotating mass in the engine. The GYT-R clutch kit and pressure plate (Hinson parts) will straighten out the clutch. Most people find the engine more manageable with a 5 or 6 oz GYT-R or Dr. D flywheel.

Be suprised if the valves need adjusted! This is not a honda man.

Basically the YZ is a race bike. You should inspect everything just like a new bike, but be ready to buy some new bearings. Great EVERY bearing in the bike. STeering, wheels, linkage, swingarm. Grease the brake pins. Check the valves, clean and adjust the carb, clean lube and adjust the cables including the hotstart plunger in the carb.

The stock clutch is pretty bad. LIke said, use the GYTR kit. Solves the issue.

FIrst thing I did is I could not ride with the stock springs. To soft. The bike had some heavier springs and installed them. Got the bike to corner. Then had the front forks revalved. Good mod for sure!

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