The 2003 Yamaha YZ450F is a big-bore, air-cooled two-stroke motorcycle. It was first introduced in 2001 and was the replacement for the 2000 model year YZ450F. The engine displacement has remained at 450cc since then. It uses an overhead camshaft with four valves per cylinder and a 4 valve/cylinder head configuration to create power output of 35 PS (29 kW) @ 8500 rpm and 25 lb·ft (35 Nm) @ 7200 rpm with a compression ratio of 9.7:1.
Look more closely. The first two, from left to right, are joined with a horizontal bar, forming the previously mentioned "H". The third vertical line is the "I", and the TDC mark.
Put the bike in 4th or 5th gear, and place a board across the swing arm, through the spokes, so it lays across both sides of the arm as near the rim as possible. Then crank the sprocket off. It's a right hand thread, so turn it counter-clockwise to loosen.
Turn both the air screw and throttle screw inward until they LIGHTLY seat. Now back each one outward one and one half turns. This is the factory setting. I am going to give you a web site where you can download a free PDF factory service manual for a YZ450FR. I believe the model is a bit different but the carbs are the same.
Go to this site and you can download a free PDF service manual. The site may take up to 25 seconds to fully load the list of manuals. It is worth the wait. www.carlsalter.com/motorcycle-manuals.asp The service procedures are there in detail and a lot of diagrams and photos. Don't mess with the pilot screw unless you have to, Part #11 in the diagram. Can I get a Very Helpful" rating out of this?
the screws on the carb are for idle speed , and air mixture, the air mixture it underneath,but it really only affects mixture at idle speed.
you may need to try raising the slide needle, or go up a size in the main jet, do one at a time and keep notes about the changes and results
It should be the small plug up near the steering head with the dip stick, you need a small funnel, use only motorcycle oil, car oil can cause clutch slip.They hold about 1.1 litres . you then need to start it for a couple of minutes then check with the dip stick
Depends on the type of carb, but you must remove needle and there is a sir-clip with slots on the top of the needle. it can be poped off and moved up and down on needle. may have 5 different spots on it. Factory setting will be the center slot. This will enrich the mix or lean it out.
Needle adjustment
Make sure everything is connected and there is a good fuse in place. To test the coil you'll want a Ohms meter and a Volt meter as well as the service manual! Make sure the readings on the meters match the ones in the service manual. Cheers!
