How do the 04 yz450f's start?

4 replies to this topic
  • saucebox

Posted May 29, 2004 - 12:50 PM


Please help me I just bought an 04 yz450 and its my first 4 stroke. The second day I had it out the kick starter broke on the first kick but it started on the first kick also. broke the gear inside and chipped the case so Yamaha warrantied it and had to put new case halves in my motor. 3 weeks later I finally got my bike back and there were bolts missing and hose clamps not tightend down and I was VERY angry with my dealer. I got it started after several kicks and rode it around for 5-10 minutes then shut it off.. about an hour later I started it back up and it was idling warming up a little and it died and I havent got it to start ever since? Are they really that hard to start or did the dealer do that poor of a job that my motor doesnt want to run now? Any info would surely be appriciated.

  • aford541

Posted May 29, 2004 - 02:12 PM


Mine starts really good, there is a technique to starting them like there was on 426 that helps a little. On mine I push the kick starter down easy till the motor gets near top dead center which is where the kick starter begins to get harder to push then I just kick it good and it fires first kick almost always when it is below 50 degrees out I turn the throttle twice to pump some fuel into the motor if it is below 70 I just turn the throttle once. My bike starts first kick almost always unless some knucklehead turns the throttle while it is hot.
I think what helps the most is an adjustable fuel screw and having it tuned correctly I use the Zip Ty racing adjustable fuel screw but there are others that are good but tuning it is the trick I turn mine in slowly till it pops on deceleration then go out .25 of a turn then it should not pop on deceleration.
I think the manual gives some good advice on starting procedures also. We had a Honda that was so rich on the fuel screw that it would only start with the hot start on.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted May 29, 2004 - 06:43 PM


You need to learn what your bike likes as far as when to choke or prime, when not to, and how much throttle to give the bike while cranking.

Any good sized four stroke is best started with the engine positioned just past top dead center after the compression stroke. With the newer ones like yours and mine, this is a lot simpler to accomplish because the auto-decompression system takes the guess work (and skill) out of that part of it. You just turn the crank until it feels like it hits compression. That's not really compression, though, because the auto comp release opened the exhaust valve as the engine went past that point and allowed it to close just after top. What you feel is the engine pulling against the vacuum created by the piston starting down in a sealed cykinder. Return the crank to the top and give it a smooth, swift kick all the way through and will cycle through to the next compression stroke and fire up.

What to do with the throttle is the most important part. When you watch a lot of 2 stroke people start a bike, you can see them rolling the throttle open as they kick the bike over. That's the thing you never want to do with your 450. Your bike has an accelerator pump in the carb, and each twist of the grip squirts a fair amount of gas into the intake. That can be useful when it's cold, but not when it's warmed up.

People are usually advised not to open the throttle at all when starting the big YZ. That is not always good advice. My '03 will almost never start like that. It likes the throttle opened just off idle and usually starts with one kick when I do that. The key is to learn to hold the throttle in whatever position and kick the bike through without moving the twist grip. It can be a difficult to acquire skill.

Mine generally works like this:
Dead cold, first start of the day, 3 full twists on the throttle, choke on, open the throttle just over idle. One kick.

Warm (like I just rode it 10-30 minutes ago) One or two kicks at idle, don't prime or choke.

If I just stalled it, I usually try one kick just off idle, no hot start. If that doesn't do it, I use the hot start and try to see where it wants the throttle (idle or somewhere close)

It can get tricky if the bike gets dropped, because it can get flooded. Get the gas turned off first if it's going to take a while to get the bike upright. To clear a flooded engine, pull the hot start lever and open the throttle wide open and hold it there while you turn the engine through slowly 3-5 times. The engine will draw only air through the intake because there won't be enough air flow at cranking speeds to pull fuel through the jets. After that, try letting the throttle back closed, or close to it and see if it will start with the hot start.

Once you get used to it, the bike should be really pretty easy to get lit up most of the time. Just have to learn how to let it tell you what it wants.

Do get that idle fuel screw properly adjusted, too.

  • Baycrosser

Posted May 30, 2004 - 08:51 AM


Well mine is brand new too and only ridden now for about 5 hours.
And what should I say? It starts always very good.
But I dont use the trottle before starting it and my dealer told me you should`nt
I also realy dont care where the dead spot is, only kick in and here we go
I love that :thumbsup: :lol:
So I realy can`t tell any negative until yet about starting a 04 YZ450F :awww: :lol:

  • saucebox

Posted May 30, 2004 - 10:32 AM


thanks for all your info guys. yesterday i hooked it behind the pickup and pulled it down the street a few blocks and it still wouldnt start up.. back fired constantly but wouldnt run. I've come to the conclusion that the dealer messed something up when they put the motor back together... which doesnt surprise me seeing they forgot to tighten 2 hose clamps and put a nut on the motor mount and a few other bolts. They're definately gonna catch hell on tues. when i get to give them a call. I'll have had it 4 weeks tues. and it spent 3 of those weeks in the shop and now its back and i still cant ride it... gonna have to give yamaha a call and see about extending this 30 day warranty thats gonna be up in about 4 days....

my guess is that they have the cam timing off.. but seeing its brand new and still under warranty i'm not gonna be out there wrenching on it. i did have it running the day i got it back from getting fixed and it seemed like it didnt have quite as much power as it used to either... before it would pull the tire up in 4th gear like it was nothing and i couldnt even get it off the ground on the pavement.. hopefully i can get a completely new motor from yamaha because the thought of them idiots opening up my motor really scares me seeing what they did to this one...

Related Content


Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

yz400f throttle bog by yz400fmaniac

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • * * * * *
  • Hot  28 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Help with 2000 yz426 by weekend woods racer

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  36 replies

YZ450F 03 Sparks driving me crazy by SirAttard

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.