Help, 16' yz450 won't start when hot.

[Lucero10x]

7 hrs on  bike.

Valves are in spec.

Also, has a pop at mid throttle.

Bought the GYTR tool and installed mxa mapping for the 16, however, their map only suggested fuel setting changes. No faults codes showing. Still mid throttle pop.

Took it to dealer they said maybe starting procedure, charged me 50 bucks and their advice on procedure is not effective, in my situation. (crack throttle slightly and kick). I should have just sent them the fifty bucks in the mail and saved my time and effort.

 

I'm kinda lost. I dropped out of a race a couple weeks ago because it wouldn't start after stalling. pushed it all the way to the truck and it started 20 minutes later once cooled.

 

Any ideas? Thanks, guys.

[Lucero10x]

I've been running 100 octane racing fuel from my local Rebel station and I am going to drain it, replace it with good ole' 91 and see if that helps (maybe the 100 octane is old in the well). I've been searching for acceleration popping and it sounds like fuel quality may be a common thread.

[MtuSmoker]

Had the same issue with my fx during a race last weekend. If I stalled the thing wouldn't start unless i let it cool down for a bit. Found that pulling the high idle knob out helped.

[grayracer513]

Had the same issue with my fx during a race last weekend. If I stalled the thing wouldn't start unless i let it cool down for a bit. Found that pulling the high idle knob out helped.

 

This has been mentioned before.  Remember that the "cold start" knob IS NOT a choke, and will not cause a rich mixture by itself.  When cold, the EFI system does the mixture enrichment.  The cold start knob is just an bleed for extra air to enter, and it can be useful in restarting a hot bike, same as the hot start knob on the older bikes.

[Lucero10x]

the cold start knob doesn't even help. My 15' never had any issue hot starting so I am pretty frustrated. Could I have got it hot and burned a valve or something. It never really had any signs of getting real hot, but I have run it damn hard.

[HORSEPOWER35]

Since you had the 15 yz 450 I'm sure you are aware of the starting procedure. Just to remind you, idle must be set properly. Put bike in neutral, find TDC and give her a smooth kick with no gas. Yes it will start sometimes if you stray from this procedure but if you want consistent starting stick to the procedure. It's not a very efficient way to start your bike during a race but I have found if you stray from the this procedure the bike becomes very hard to start.

[grayracer513]

Put bike in neutral, find TDC Compression and give her a smooth kick with no gas.

 

Fixed

[Lucero10x]

Changed the fuel. Seems to have helped. Real test will come at the WORCS race Saturday. Thanks, guys.

[motohead13]

The efi system adjusts for cold/hot starting on its own. Probably a bad sensor.

[Piney Woods]

The efi system adjusts for cold/hot starting on its own. Probably a bad sensor.

I am getting ready to buy my first efi 4stk, what is needed to find a bad sensor?

[motohead13]

I am getting ready to buy my first efi 4stk, what is needed to find a bad sensor?

Its just trial and error