YZ450F Starting problem

I know that you have discussed this in the past but mine is different.

For starters I live in Tampa,FL but I drove to Tennessee to get the bike. So I am not sure if the stock settings on the pilot screw is different.

When I first got the bike I already did my share of asking how should I start this four-stroke (I have always had 2-strokes) and everyone told my not to use the throttle at all. Even keep my hand on the handlebars not the throttle when I kick it. Which I tried.

Here is the deal. If I stall it or drop it, I have a terrible time getting it started. Here is how I do get it to start though when I can. I Hold the throttle wide open. You guys are going to think I am crazy, but I swear that when I try the regular way of starting and when it does not work (Which it usually does not) I slowly turn the throttle to almost wide open and usually within a few kicks it will start (but it does burble at the beginning, then it comes around and starts). However there are times when it will not start at all. When the bike is cold or not real hot it will start. I think this is telling me that I am running to rich in the bottom. What do you think? I think I might need to mess with the pilot screw (which on a two stroke we call them air screws) which according to my manual it works backwards than normal. I race harescrambles and it is just killing me in my times and energy out on the track.

Please give me some advise. And what gas is everyone running? Would that make a difference? I am using 93 Octane from the pump.

Thank you,


I didn't see you mention pulling the hot start lever.

Yes, I pull the hot start everytime when it is hot.

Adjust your fuel screw IN until you get slight popping on deceleration (if the idle hangs then you went too far). Then you should be lean enough to start pretty easy when hot. I adjust my fuel screw almost every time I ride, depending on the current temperatures.

And by the way, opening the throttle all the way while starting is essentially leaning out the start/pilot circuit. So you are right on the money with your technique!

Is the fuel screw and the pilot screw the same thing? My manuel says that you turn the pilot screw in to lean and out to richen. Waz up?

What gas should I run?

Sorry - typo'd that reply. :)

The fuel screw and the pilot screw are the same thing. OUT is richer and IN is leaner.

I do that all the time! I edited my post above to reflect the correct behavior.

BTW - I run premium pump gas and have never had a problem here in Houston. I buy from a high volume station so I assume it's always fresh. But if I ever start having jetting or fuel problems I'll switch to a race fuel.

Anyone else ever open the throttle and kick their bike, I just went and tried it, it blows right throught the stroke like it has no compression, that was wierd. It runs like a raped ape though.

Depends on which side of the slide the screw is on. I forget which one is called what, but the screw on air box side controls the amount of air that hits the pilot jet and the carbs with it on the engine side controls the amount of fuel through the pilot jet. I might be backwards but I know that is the reason you are used to calling it the air screw. Someone correct me if I'm wrong!

As for starting with the throttle wide open, my 426 will not even try to start like that. Best thing to do when it's flooded and the hot start button wont work is to turn the gas off and pull the compression release in and kick the bike over several times to help get the excess gas out. On my old XR, the only way to get it started after dumping it was to hold the throttle wide open but it didn't have the throttle position sensor or the accelerator pump.

As for starting with the throttle wide open, my 426 will not even try to start like that.

Man - I should just start over. :)

I didn't really mean to encourage that. Just that by letting in more air , he was on the right track.

Maybe I just need to log off for tonight - LOL!

I knew what ya meant, I was just explaining myself about how much it helped on bikes before they got high tech. Time for me to sign off as well... I'm rambling. :)


It's got to be jetting. My 450 in Orlando starts every time on the first kick. No matter what the conditions it starts on the first kick. That is one thing I really do love about this bike.


So can most of you guys start your bike in gear? Like first gear?

A 2 smokes air screw regulates how much air enters the pilot circuit, where the fuel screw on the yamaha's regulates fuel. Simple. Dont be shy about using it. It works wonders quickly. Get a Kouba fuel screw makes it much more convenient. Motoman's site show how to make an extension cheaply. Good Luck, it is jetting that is your problem. Gas can also be a problem, do they use oxygenated fuel in your area? If so go to race gas or some other source than the oxygenated fuel as it runs like crap.


Can you start yours in gear?

I start my bike in gear almost every time I start it except for the first start of the day.

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