Cold motor?

Just got a 2006 yz450, I've noticed the bike stalls out if I pin the throttle from idle when the engine has only been running for a few minutes, the issue seems to go away once theo motor is real hot, and I don't really ever need to do that on a 450, but still I think it shouldn't stall...what can cause this?

Assume it's not a jetting issue or bad gas

if you pin the throttle with a cold engine it's going to stall's normal.... Also pinning the throttle when a engine is cold could also lead to some damage.....

If the motor runs well @ operating temp, and starts well don't screw with it. A properly tuned carb motor will never run well cold and even newer injected motors run poorly cold. OPERATING TEMP is the key.

I'm not at all certain why people expect the bike to be able to tolerate that, but the engine responded in a normal way.  In fact, if properly jetted, you should be able to shut the engine down from a warm idle in neutral by slamming the throttle wide open instantly.


The thumper gets one intake stroke every two revolutions.  As it sits at idle, the vacuum of the intake stroke pulling against the closed throttle slide lifts fuel up through the pilot jet to enter the airstream.  If the throttle is opened in any reasonably normal manner, the vacuum drops of considerably, but the combination of the squirt from the accelerator pump and the cut away in the slide help boost the main circuit into operation and keep the engine running as it transitions from the pilot circuit to the main.  If the throttle is opened to WOT in a snap, the vacuum simply falls to zero, and not much of anything goes anywhere.  The accelerator pump squirts, but the slide cut out has no opportunity to assist the startup of fuel into the main circuit, and the engine gags and dies.


100% normal.

I figured, still getting used to this 4 stroke thing.  so different from my ole smoker!

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