Hard to start and stalls easily

This is my first post on TT and also my first few weeks with a 450F. I came off of a YZ125 to this bike and man, what a difference! I am very knowledgeable about two strokes, but have a few questions about the thumpers. My bike has the stock headpipe and the rest is a FMF Ti4. The bike has been rejetted with the FMF supplied jet kit, and the bike runs like nobody's business, but is really hard to start and likes to stall pretty easily off idle.

The idle speed seems right, but the bike is really hard to cold start even with the choke on. I am not touching the throttle at all, so I don't think it is flooding. I have even tried just a little blip of the throttle before starting to allow the accelerator pump to put fuel in the carb. Any help that you guys can give me would be really appreciated. I think it might be running a little rich, but am not sure.


2 words


fuel screw (adjust)

I have read alot about the 450's needing a flywheel, so I am sure that I will be ordering one. When started, the bike puts out a little black smoke at first, which would make me think it is rich. I could be wrong, just need other's opinions! How much should I adjust and which way? What I am really concerned about is just getting the darn thing to start a little easier!

if its rich now turn in the screw a half turn,its hard to get to you might think about investing in a zip-ty a/f screw which you just turn by hand. these bikes are very temp. and altitude sensitive and need adjustment frequently,its well worth the $20 :cry:

I have a 426 and I always have to prime it with 2 full twists of throttle when I first start it for the day. After that I NEVER touch it again. My buddy just got and 03 450 and he has troulbe getting it started the first time. We think we may know why. Prior to this he rode a YZ400F which since it does not have and automatic decompression release forces you to find TDC. Then pull the release and nudge it past before you give it a solid kick. Well, it seems he was getting lazy on the 450 and just kicking it over and over. Like you would on a 125, incedentally. When he got sufficiently tired and pissed, I gave it a try. It was not intentional but he noticed that I was finding TDC (habit?) and nudging it past before kicking it. In aobut 5 kicks I had it running. With a 125 you may have been making quick stabs at it but with the 450, you need a good solid kick all the way through the stroke of the kick starter. I think you jetting is probably close enough that it is not affecting the strating. Once it is running, you should notice the occastional pop on decel but not much more. If there is absolutely none of that, you may be a bit rich on the fuel screw but I am not going to promise that is the case.

Most guys think the 450s are more or less a mindless affair to get started but I have to dissagree. You can't just kick and kick. Find TDC is still the most reliable method for getting it to start every time. My 426 is more reliable in this regard than and 450 I have seen but then it does force me to use this method.

They are not hard to start, just very different from a 125.

Oh yeah, I stalled the heck outta his 450 until he put an 8ox flywheel weight on it. Definitely go that route, it will help alot.

Thanks alot guys, I really appreciate all of the help. I think it would be safe to say that I have been trying to start it like a 2-stroke. Bad habits I guess. Which way does the fuel screw go to lean it out? Is it clockwise or counter-clockwise? I have the manual and I need to read up more on it. I couldn't exactly find the fuel screw either. Where the heck is it? I know that makes me sound like an idiot, but this carb is alot different from the 2-strokes.

And as a general principle, would you need to run leaner or richer with cooler air. I live in Fort Worth, Tx, and it just got about 20 degrees cooler in about a week. The last time I rode on a track it was 90 degrees, so if this bike is really temp. sensitive, I would figure that I need to change it. Any ideas?

The fuel screw is on the bottom of the carb. You have to rotate the carb to get to it. This is a pay. ZipTy racing and others make a replacemnt fuel screw you can adjust with your fingers. You can also buy a realy stubby flat head screw driver to get to it as well.

Colder air is more dense and there for requires that you richen the mixture.

If it is too lean it will pop on deceleration and have a hanging idle (takes a while to return to the lowest RPM after a blip). It will also be hard to start when cold.

Does it have decel pop or hanging idle?

How do you set the fuel needle? If the bike is idling and you turn it in or out what are we looking for?

What range are we looking at? 1.5 out to 2.5?

Is the Bike New or Used?

If Used one of the issues for hard starting could be the Carb needs to be cleaned. And or the valves may need adjusting, if Used.

Hard starting four strok

:cry: never heard of it :cry:

It does take a little to get used to in starting these beasts.

Here is a good place to learn the drill

Full Proof Starting

I know you have a 450 but the same dynamics used for the 450 as well

The bike doesn't have a hanging idle, it cleanly returns to original idle speed. It does pop on deceleration though. I guess I was wrong and actually need to richen it up a little.

Thanks John, that was a lot of help. The bike is used, but the valves were adjusted about 10 hours ago. It is a really clean bike that had very low hours on it. It could be possible that I just need to take apart the carb. and give it a good cleaning. Not sure how to do that very well, but I guess I will learn as I go!

A little popping on decel is OK, as long as it doesn't have a hanging idle.

Sounds to me like it just needs a half turn out on the fuel screw. I would try that first. If it's still hard to start when cold, then give it one or two blips of the throttle.

My YZF hates a blip of the throttle and instantly fouls if I do that.

My CRF on the other hand WANTS me to blip the throttle at least once sometimes twice (when cold outside). Even with the jetting pretty well dialed.

Go figure.

Also - John_Lorenz's suggestion of a cleaning of the carb is good. Just don't put the slide plate back in upside down or it will run like crap.

i had the same problem with mine just pull the choke first then turn on the fuel and twist the throttle all the way and release two times then kick it. do not give it any more gas it should start on the first or second kick hope it helps. :cry:

FMF jet kit, oh boy. They are never real good on their jetting specs for most bikes and quads.

Anyways, you should look into the JD jetting kit. If you have the bike jetted right on, it is very easy to start. I have to use the choke and blip the throttle twice when cold, first kick when hot. Also make sure you have a clean plug, that really helps with starting.

Be sure you have the adjustable fuel screw, makes fine tuning the carb very simple. That is a must have $25 item!

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