2014 yz450f w/ 14 hours running bad

This bike was running perfect. The first problem I noticed occurred on a ride last saturday. After about 30 minutes on the track the bike felt like it misfired. I continued to ride and it happened two more times. I pulled off the track and changed the spark plug and the bike seemed to run ok for 20 minutes and I went home. My next ride was on Wednesday and the bike started fine and ran fine during its initial warm up then when I put it in gear to take off it died. I kicked it about 8 times and it would not start. I pulled the cold start button and it fired up. When I pushed in the cold start and tried to go the bike died. I was able to get the bike running and made about two laps but it felt underpowered. I pulled off the track and with the bike in neutral and running I noticed that it was not reving

I took the bike home drained the gas and put new gas in the bike. It starts fine and has good throttle response when cold but after it runs for a few minutes the throttle response becomes slow and it's not running as smooth as it should. So I've put a new plug in and new gas. Cheched the coolant level and it's normal. I change the oil and air filter after every ride. I have not checked the valve clearance but it runs normal when it's cold so I'm not thinking that's the problem. If anyone has an idea what the problem could be I would appreciate hearing from you. Thanks.

What does the spark plug look like? Also have you got a GYTR tuner you can plug into it to see if it gives you any fault messages? sounds like fuel pump or an electrical connection is loose.

Any codes on the tuner? Are you running one of those fuel tank vent caps? They've been known to stick and prevent the fuel tank pressure from equalizing. This causes a vacuum within the tank and the pump can't provide adequate pressure. Usually resulting in the symptoms you describe.

Check the timing. Seen a few jump a few teeth.

I rode the bike around my property last night to verify I have a problem. The bike starts easy with the cold start out. It runs perfect during warm up. I rode it around for a few minutes and it ran great. I stopped and put the bike in neutral and the throttle response was horrible. It was very slow to build rpm, it backfired through the intake and died. I was able to restart the bike but it was running pretty bad.

This bike is 100% stock.

The spark plug looked good when I changed it.

I don't have a tuner.

When I looked in my manual it talks about a FI diagnostic tool. I Google it and as far as I can tell it no longer available.

I called the local dealer and they can run a diagnostic for me. I would buy the gytr tuner if it had the diagnostic capabilities I'm looking for but I'm keeping the bike stock and don't feel like I need to change the stock map.

I'm going to check the valves and look for any loose connections this morning. Thanks for your comments.

The tuner does have limited diagnostic capabilities.  It can pull trouble codes, but it does not have the ability to run tests on the system components. 


The FI diagnostic tool used in the shop by technicians should be available as well, but that will be somewhat more expensive.

Checked valves. Intake measures between .003 and .004 (.089mm) the spec is .13 to .20mm. The exhaust valves were between .007 and .008 (.19mm) the spec is .20 to .25mm. So I will adjust valves and see if that fixes it.

Thanks for the help. I adjusted the valves and runs excellent.

That's crazy. my valves are still in spec at 48 hrs.

That's crazy. my valves are still in spec at 48 hrs.

Whats even crazier is my valves are still dead on at nearly 140 hours. 

Whats even crazier is my valves are still dead on at nearly 140 hours.

well that's great news for us!! Glad there holding up great.

Whats even crazier is my valves are still dead on at nearly 140 hours. 


That's good to see.  What kind of air filter/oil/oil filter are you running?

That's good to see. What kind of air filter/oil/oil filter are you running?

I run Amsoil 10w-40 and the cheap RMATV Nuetron oil filters. Change it on average at 6-7 hours. Air filters are stock and GYTR. I just clean them as needed, no set interval. Honestly don't think I'll buy the GYTR next time, they seem to let a bit more crap through. My 2012 had the same routine and only needed 1 minor valve adjustment in 170+ hours before I sold it.

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