2012 YZ450f hard to start after warm

The ol bike fires up just fine from a cold engine but after 10 mins it is very hard to start. Sometimes when I'm trying to start it, I can hear what sounds like the piston rattling.. is this typical? I have 25 hours on it. I am new to the four stroke engine.. Any suggestions? Thanks

Stock mapping? Starting can be a problem if you remap it.

You should not give it any throttle when starting, but sometimes when it is warm I find craking it a bit gets it done (I am using MXA's recomended map). Make sure you are on the compression stroke. Set it up to where you just start to feel compresison and then relase the kick started so you can give it a solid kick from the top with compression just beginning.

Edited by BBrown626

My 2011 has been a bitch to start when warm, but seems to be getting better. It still has less than 20 hours on it but has gotten better since new. Last weekend when the engine was HOT from riding tight single track with long hillclimbs and some stationary idling it started the best ever. I'm hoping it's a sign that it was just tight from the factory and a really good heat cycle is loosening things up.

I think I am currently running the drivability? map.

Stock mapping? Starting can be a problem if you remap it.

You should not give it any throttle when starting, but sometimes when it is warm I find craking it a bit gets it done (I am using MXA's recomended map). Make sure you are on the compression stroke. Set it up to where you just start to feel compresison and then relase the kick started so you can give it a solid kick from the top with compression just beginning.

I have not messed with any mapping. I keep hearing about that but need to do more research.

Do you think that I need to check the valve clearance?

my 2012 is hard to start when hot sometimes as well. I have found "as others suggested" to make sure I kick at the top of the compression stroke and it normally fires. Alot of times I find pulling the Cold start/Idle nob out usually make it fire right up.

If you need to pull the choke out when starting, after it has warmed up, you are too lean on the bottom end. Normally I'd just say go up a pilot jet size, or adjust your fuel screw, but it sounds like you need re-map your bike.

The cold start knob on an EFI YZ450 IS NOT a choke or an enrichment valve. It simply adds air, the same as opening the throttle slightly. A lot of people have reported that their bike starts better when warm if they use it.

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