Still having problems starting the YZ450!!

I'm ready to give up. My 426 really spoiled me. First or second kick every time no matter how many times it flipped, how cold it was, or what ever....This 450 takes 10-20 kicks when it is cold. Here is what I have tried:

1. 2-3 twistes on the throttle, no choke and kick. Tries to start but still takes 10-20 kicks to start.

2. no twists, no choke and kick. 10-20 kicks to start.

3. The above two with the choke and kick. 10-20 kicks to start.

4. Hot start pulled (again this is all when cold)5-10 kicks to start.

The air filter is spottless along with the airbox tubes (not sure what they are called), the carb was cleaned ( brand new, it wasn't dirty or clogged ). At a fast idol, I tunned the fuel screw out 2 1/4 turns. The plug is greyish tan. No backfiring occures on deacceleration. At 1 3/4 -2 turns out on the fuel screw, the bike would run lean and backfire. All other jets and settings are factory.

Even when the bike is hot, starting it is very inconsistant. Most of the time it starts up within a couple of kicks then sometimes it takes 10-20. Once running, the bike rips!!

I live in south Florida, humidity is high along with the temp. Any help would be greatly appreciated!!! :)

Some one will come along and give you better instuctions than this but I think you need a smaller pilot jet. Anytime you run your fuel screw at more than 2 turns out you run the risk of losing it. Drop down one size on your pilot jet and maybe someone can tell you what air jet to run because I don't know. If that doesn't work it might be something electrical, but I can't help you at all when it comes to that.


The 250F guys are having CDi problems...wonder if yours may be bad as well?


How many hours on the bike? Replace the spark plug, replace old fuel in cans with fresh fuel, clean air filter and adjust the fuel/air mixture screw. Normally, the bike will start within three kicks when the temperature is above 50 degrees. When the temperature is below 50 degrees it may take 10-15 kicks to start. When it is warm the hot start isn't always needed. Kick once or twice without the hot start, then if it doesn't start use the hot start.


It might be worth checking the valve clearance,especially if it's erratic starting. It's possible they might have been a little off from the factory. Not likely on the yzf's but it can cause the problems you describe. Worth a check and a minor adjustment if needed.

If the bike would start in 2-3 kicks in warm weather if you went to the next size up pilot when cold it should start in 2-3 kicks also. As of yesterday I experimented with every pilot from 48,45,42 & 40. The bike would start well with any of them! I am going to a 38. I just switched to the EJP needle and have to change everything else. But I will get there soon (this weekend). I am sure it will rip again!


If you make the pilot circuit rich, will it effect the 0 - 1/8 throttle when warm?


So bottom line, do you guys think the bike is too rich? Is this why I can start the bike easier when I pull the hot start (warm or cold)?? Doesn't the hot start lean out the carb??

So go down one size on the pilot jet.

Check the valve clearance.

Maybe, go down one on the needle clip.

Does this sound right??

I am not the most knowledgable person, but doesn't the choke richen the mixture, to make it start easier because the gas will stick to the cylinder wall because of condinsation. Now if that is the cause and the bike is running that rich, wouldn't the bike run like CRRRAAAPP spitting and sputtering while running. I think its the valves.

No where in your starting methods do you mention NO twists of the throttle and choke ON. First stop twisting the throttle, 2-3 twists is MOST CERTAINLY flooding that carb/motor. Second if it's cold the thing will not be easy to start with the choke off.

Here is how I start my 450 and from the first start, until now I have not ever kicked more than 3 times:

COLD: choke on, kick NO THROTTLE TWISTS AT ALL (unless I let it run with the petcock off at the end of a ride, then I twist ONCE to prime the carb)

HOT: Choke off, and kick. I don't even use my hotstart lever, it starts without it

HOT and if I stalled it: choke off, kick. Again I don't use the hotstart lever.

Of course also follow the advice of others and make sure that your plug and all has been changed properly.

Oh by the way you need a richer pilot jet, you shouldn't be more than 2 turns out on your fuel screw.


I know you have your 426... but.....

did you slap on afreshly oil air filter and start it? or have you started your bike after you just washed it? If you answer yes to any of the two questions.

You might have clogged the slow jet. Time to clean all the carb jets.

No problems in So-Cal EVER (99 400YZF, 02-250F, 03-450F)

btw, i am having problems starting my Red Machine? any helpful ideas? to much compression I think........


Yeh, In all the frustration, I just forgot to add that part about not giving it any twists. I did that too. Like I said, it seems the only way it will start is by pulling the hot start lever in. So you think I should go up one size on the pilot jet? Here's the bad thing about owning a two stroke and a four stroke. I start confusing myself on what does what. :)


No, I sold my 426 to get the 450. The 450 is 10 times the bike, if only I can get the starting thing under control....

Whenever I have tried to start my 450 with the choke on it won't start until I pull the hot start once and let off then kick it and it starts right up? I'm like you nothing, but 2 strokers before and I am still learning the basics of a 4 stroker. Going to take my bike over to a seasoned 4 stroker and he will set it up for me and school me in the process.I know I use the hot start more than what's needed, but hey it starts! Then the fun begins. I bought the power now, but am going to have this guy instal it so it all jetted right. Wouldn't trade the 450's hit or raw power for anything. This bikes a blast!!!!!!!!!!!!!!. JUST PIN IT!

03 450, works frame guards, acerbis, power now

Once you get the knack this will work all the time.

It's 30 degrees out bike hasn't started for 2 days.

Turn gas on,Choke, Hot start pulled in,

No twisting throttle.Dont just flat out try to kick the snot out of it,,That wont work.

Try this technique, Just try it.

Kick half way down,then up,

then one full kick in one fluid motion all the way down.

It's kinda like a pre-prime kick.

If that doesn't work then try the other clues that are posted.. But I think it'll work. :)

It works for the Baby-F every time,even when I dump it.

Sometimes after it's warm I dont even have to kick a full kick to get it lit,just half.

See Ya,

If you are having to pull the hot start to start it even when the motor is cold it needs to be leaner. Go down 1-2 sizes with your pilot and it should resemble what you are doing now with the hot start. The power now is a simple installation. You shouldnt have to have anyone install it. Jetting is a little bit of a time consuming process but once you understand it,the knowledge is invaluable. It shouldnt take you but 10-15 minutes even if you have to pull the carb off after you do it a few times. You can remove the carb with out removing any body work or the seat.

I start my 250F the same way I started my 96 CR250 after it has been sitting for a week (in the garage).

I turn on the petcock, pull out the choke, lean it over until fuel runs out of the carb overflow, and kick it with NO THROTTLE.

Usually starts 1st or 2nd kick everytime.

Try that before you go messing with the jets.

Let us know if that works.

Have you changed your plug? I just fouled a plug last night that had only .6 hours on it. ( Yamaha hour meter helps with maintenance intervals) I took it out and it had spark. I guess just not enough to spark the fuel. I installed an new plug and one kick later it was running. Might be a cheap fix for all your headaches.

fatmancantfly, now that you mention it, the stock plug that came in my bike lasted about 2 rides.

It crapped out before we could start our 3rd ride. Couldn't get the bike started.

Been using SPLITFIRES ever since with no problems.

I had to go up a size on the PJ and richen up the clip because of a new exhaust,because of popping,crackling,backfiring. :)

Sometimes I dont even have to kick it hard at all,just fall on the lever a few times real slow and it'll start. :D (cold) I'm confused.

As to jetting this bike?

It sure is alot easier than the Red one, IMO.

Access,I mean.

Thanks Fastest1, for your info.

I was alittle confused cause everyone around here was richening their PJ's by 2 sizes except me.

I just always started my bike with the Hot Start pulled. :D

Maybe I should try it without. I dont think I have.

I'm going to check it out now.

And what's the benefits of the Power Now thing? and why?

Thanks in advance. :D

See Ya.

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