2005 YZ450f wont start..

Had it running a couple weeks ago when I bought it but it was very hard to start and didnt run very good. Now after I got new jets in it it wont start. How do I check the timing? Any other ideas?

Why did you re-jet it? What did you change it to?

I rejetted it because I had the carb taken apart to clean it and I thought it may be why it wasn't running so good.

I changed it to 48 pilot and 170 main because that's what the guy at the shop told me to do. Our elevation here is 500ft

Your jetting doesn't sound far off. How many turns on the fuel screw? I would set it at 1.5 turns out and give it another try. The rough runing was most likely junk in the carb. If you got it all back together corectly it should fire up. With the engine cold, fuel on, pull the choke, twist the throttle 2 times (pumps a little fuel in the engine), close the throttle, and kick it over. If nothing else is wrong it should start in a few kicks.

That sounds a bit on the rich side to me, try using the hot start to start it cold. If it fires up quicker with the hot start you it's jetted too rich.

I will take your tips and try again tonight. The dealer actually told me 175 and 48 on the jets but they were out of 175. I was running 45 and 165 before. It probably sounds rich because my elevation is a lot lower than many members on here I think.

Like I said, it was running before but not real good and it was still a bitch to get it to start.

I bought the thing about a month ago. Never had a 4 stroke before but I couldn't pass up the deal...paid 1000 bucks for the thing. Previous owner said it had a new top end in it last fall and it hadnt been ridden since and it may not run real good because it was sucking too much air because it didn't have an air filter. And that the top end hadn't really been broke in yet.

I put a brand new air filter on it. Put a brand new plug in it (the old one wasn't bad). Checked the valve clearances and they were all good. Checked timing while I was in there and it looked good.

Tore the carb apart. Cleaned it. Put new jets in it. Didn't check the needle...thinking I should tonight and see if it's on stock setting. Screw is 1.5 turns out.

Not sure where else to go with it. Really want to ride it this weekend. If I can get it running, it might just need a good ride.

Any ideas? I'm gonna go back at it tonight.

I was running 45 and 165 before. It probably sounds rich because my elevation is a lot lower than many members on here I think.
I run 45/165 in my '06 as my summer jetting (45/168 winter) at altitudes ranging from 3700 down to -80 (not a typo). The 48 is a bit rich. The 175 is just ridiculous. However, I don't think that would keep it from cold starting.


Took the bike down to St. Joe State Park in Missouri last weekend and took my 1993 Husqvarna 360 as a backup.

Ended up riding the 360 most of the time.

Here's the deal now. The 450 will start first kick cold. Starts great. Now my problem is that throughout the middle RPMs the bike will bog real bad. Runs great at idle and runs great when you're riding the hell out of it, but anywhere in between that she wants to bog. Also after you've ridden it and it sits a while, it doesn't want to start back up. I'm mainly concerned about the bogging right now so I can at least get it running good to sell.

Possibly leak jet problem? Where should I go from here?

If you had the slide out, check the vacuum release plate on the back (engine side) of the slide. It's a common mistake to replace it upside down. The "square" edge with the hole in it needs to be on the bottom. People tend to reinstall it with the round edge down because it looks right, but it's not. Check the picture in the manual.

Also check the AP, if the bike sat for a while the jet could be clogged and not squirting fuel. I ran into that issue with my bike, solved what I thought were jetting issues.

I'm having the same problems with my bike... I have a 05 Yamaha YZ450F that will not turn over. It started with a bog/hesitation & pop sounds than shuts off completely. Values checked 100% and are good. Air filter checked and good. Fresh gas & oil, new spark plug, added a new fuel screw, cleaned carb 100%. Far as the top/bottom end is concerned in my opinion I believe they're all good because I don't ride it everyday or every week. I have a rebuild carb kit coming this week which I will install it just in case. Do you all think I'm over looking something that needs attention? Maybe the float is stuck or something like that!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now