2007 Yamaha yZ 450 F - Answered Questions & Fixed issues

Two thinks i can think of are cleaning the spark plug. and/or adjusting the idle screw on the side of the carburator untill the engine sounds normal.

it has one on the oil filler plug if you have no sight glass on the side of you crank case cover. if your missing the dip stick simply buy a new dipstick. or you could check the amount of oil necessary for your bike (750-950ml) usually and drain your fluid and replace the oil with new fluid. measure it out in a measuring glass made for liquid. then your reassured you have full oil if your worried. be reminded tho that the oil lubricates your ****** as well as your wet clutch so either way oil is quite vital

If you just doing periodic oil change then 1000ml if you are changing oil filter aswell then 1100ml
regards Jamie

Question edited for clarity and add maker. Question moved to model category. You may find the casting broken inside the crankcase, but as there is a 'Kick Start Kit' for this bike, it makes me think that they know there is a problem with it. https://www.google.com/search?q=2008+yamaha+yz450f+kickstart+kit ..

Even when I run my bike pipe is so hot cant ride safely as I have to lift my leg out of the way bc pipe is burning hot. Without touching it already have burn scars on my leg.

It could be the pump getting a little old and sticking. Is this an external pump or one in the tank? The pumps generally work on some sort of demand or pressure system. Is this injected or carbs?

Sounds like the carb floats are sticking. Allowing more fuel to enter the combustion chambers than can be burned off. Have the carbs checked/services asap. The air/fuel ratio must be right for the engine to perform at peak performance. Hope you are changing that oil too! Good luck

Does the decompression valve operate when the lever is moved? As the engine turns over easily with the plug out, but not with it in, I would have to suspect the decomp valve,

the is few possibilities with this issue but my first thoughts would be leaking intake valves or maybe one has stuck open or they might just be worn out allowing compression to blow back through carbie, My next thoughts would be are all the breather hoses on the carbie clear and free of blockage maybe one has melted from heat or got blocked from mud debree etc? Check valve clearance or get leak down test done would be my first recommendations.Cheers... Motoxpartsonline.com

ok buddy try this you will see on the carb a little screw try fiddling with this screw if it makes no difference get back to me its the air mixture screw in pic below

Carburation! If the air/ fuel mixture is not carefully adjusted by the choke system after warmup it will do just what you describe...check it out!

It clamps around the cv.Just give it a good yank and it should pop right out.Yes they just pop out. Pull as straight as you can and give it a good **** and it should come out.

.Procedure is easy enough.
1. Remove wheel.
2. Remove axle nut.
3. Take a-arms loose at the 4 mounting points on the inside.
4. Slide axle hub and assembly off axle.
5. Give the axle a good tug and it will pull out of the differential.-------- In terms of pulling apart the CV joint...once you take off the clips does it seperate easy? ------- To pull the axle out of the diff, you need to put your two hands on the outside cv, and yank it a couple times. The inside cv has a clip that will not let the goods come out of the inside cv cup. You really have to pull on the axle sometimes to get it out. Use the plunging side as a way to gain momentum: push it in then pull it out as hard as you can and it should come out. I've replaced several axles on 700s and 660s and 450s and doing so does no harm to the axle.

Yes, you have to take the axle out, because the inside cv is the only side with the clips. Theres the clip on the outer edge of the cv, pull that out, then the axle and bearings come out of the cv. Then on the end of the axle, theres a clip the holds the bearings and the cage on. That slides off, and you can now replace the outside boot. On the boots, you might be able to re-use the bands, but you may want to get new ones because the old ones might not clamp hard enough. Its a straight forward project.

Auto zone or napa sells the bands that you can tighten. the bands that are on the oem stuff need a special hand tool. ----- Be careful when pulling on the axle, since the inner joint is a plunge joint and you could cause damage if you just reef on the thing. once you get the axle out place it in the vice. you should buy a brass punch for dissembling the outer CV joint. give it a good whack and it should pop off.You can use a tack hammer ,you can buy at home depot for $7.00.-------- Also for more details, click the link below:--- http://www.ahwooga.com/atvcvboots/yamaha.html --------- This will help.Thanks.Helpmech.

This can happen if the fuel tap leaks , and the engine fills with fuel.
kick it over with the plug out, and ignition off , and see if petrol blows out the plug hole.
it may take 20-30 fast kicks to clear it

OK to check oil level you have a little dip stick on the left hand side on the frame of bike just in front of the fuel tank to check this dip stick you need to start the bike and idle only (not rev up or ride) and you idle the motor for 2-3 minutes with the bike in upright position. then turn off motor keep in up right position and remove dip stick - wipe the stick clean then insert dip stick back in its hole (without screwing in) then remove it to see oil levels.
a good quality 20w-40 weight oil (motor bike specific) is a good choice but pretty much any decent oil from your motorcycle shop would be OK just discuss it with them when you purchase it I not sure what country you from but where I live our Yamaha shops sell Yamalube and this is perfect a bit pricey but for our favourate toy, it is worth it!
To fill the oil there is another plug on left hand side again at the front end of the motor you will see it is the only plug there that can be opened with fingers - you will need a funnel to fill cleanly as is pretty difficult to pour into it with out spilling otherwise?
Your bike holds only 1.2 liters (1200ml) of oil in total so if you not changing oil filter and completely emptying then oil lines, only add up to 1 liter for a simple oil dump and refill.
Hint for the day with oil is - On a MX bike the more often you replace the oil the longer it will last before needing repair I would always recommend changing oil either once a month or every 3 hours of riding use which ever comes first !
I am often told I am over cautious with this oil change strategy but I also have YZ450f 05 and a 2003 model and I have never had to rebuild because of break down or fault with motor
Maybe this is coincidental ? but then again - Maybe not ??
good luck hope this helps a little
regards Jamie

I'm assuming the 450F oil system is the same as the 250F... all I do is drain through 3 spots - the bolt near the shifter, the frame bolt, and the filter cover. The only time I removed the "Y" shaped oil line thingie was when I put rings in my bike and decided to tear a bunch of stuff apart. I also removed the oil strainer in the frame at that time and had to have Red break loose the frame oil strainer bolt for me. He just used a big wrench and twisted it loose. To my surprise, I found pieces of tree/stick like stuff in the frame strainer.

For filters... I immediately went with a Scotts stainless steel filter. Yeah it's $80, but it'll be the last filter you buy as you can easily clean and reuse it. I figured the stock paper filters don't last too long, cost $10 to replace, and you have to worry about always having a spare.

0.7~0.8mm (0.028~0.031in) - On a 2004 at least.As noted here:http://m.bobbitt.home.comcast.net/~m.bobbitt/yz426fm/yz426fm.html

clean carboretur,carbonize your muffler

The most common answer you will receive for this question is more than likely check and clean your pilot jet and pilot circuit with compressed air and new pilot jet ideally. I must confess in most cases this does apply except the last 3 rebuilds I have done on 400, 426 and a 450 YZ exactly the same problem where hard to start and when started only wanted to run with choke on they all ended up being leaking intake valves
Best option if you can is clean pilot circuit replace pilot jet - Then double check your valve clearances (sometimes to tight can leave the intake valves hanging open when meant to be closed) then if still no joy, Do a leak down test or get your local shop to do leak down test - The leak down test will save you a lot of frustration diagnosing internal issues. Just to clarify don't pay too much attention to the percentage loss of the test just do the test to confirm if there is a leak or not.
good luck - Regards Jamie

The high and low reving can mean it is too lean which will also explain the ovrheating.
clean the carb
check the valve clearances
check for air leaks on intake manifold.
if you have non standard exhaust it may need rejetting

there should be a dip stick, depending on the model there are a couple of places it could be, up on the frame or hanging off the fill cap, yours may have broken off.
They hold aprox 1.1 litres, but you may need to buy a dip stick.