HELP! 2010 YZ450 sputterd and died. Will not restart, very confusing!

Hi guys,

I have a big problem with my 2010 YZ450f and was wondering if anyone could give me some insight on the matter. I have been a proponent to FI on motocross bikes... but right now I am changing my thoughts!!

FYI, the bike has 72 hrs total. I replaced the piston last season @50 hrs and have since put 22 hrs on the replacement stock piston.

Second ride of the season, started without issue (second kick) after 3 laps on the track.. riding slow in first gear to the truck the bike sputters and dies. Kicks over fine, but would not restart. As a note, during my first ride of the season the bike died while idling warming up, was hard to restart but did eventually and ran fine afterwards for about a 1.5 hr ride with no issues.

This is what I have done/checked so far:

Checked spark- good (replaced plug anyway)

Checked ECU- good (swapped from running bike)

Check ed Fuel pump – good (swapped from running bike)

Checked fuel injector- good (swapped from running bike)

Checked FI capacitor- good (swapped from running bike)

Check ed rectifier/regulator- good (swapped from running bike)

Checked ac magneto- good (resistance checks)

Checked tps- good (resistance checks)

Checked valve clearance and cam timing - good.

On the FI tuner no error codes show up.

When I pull the plug, it seems dry to the touch... ie it is not getting fuel and makes sense why it died on the way to truck but cannot figure out why.

Basically where I am at would be to buy the FI diagnostic tool and see what code it gives me because I basically ripped apart an entire running bike aside from changing the wiring harness to no avail. FYI when the other bike was put back together it runs fine.

Any suggestions other than the FI diagnostic unit?

Edited by Davey762

bad throttle boddy?

clogged fuel path?

Is there an injector pulse? How about coil, is there visible spark? Since u say plug is dry, i would check for pulse at injector, and if it pulsing, check to see if something clogged in line.

Throttle body? I dont know... thats one thing I never tried to swap out but can you explain why you think it could be that? A new injector didn't do the trick and the TPS sensor checked out ok so I'm thinking the throttle body is ok.

What is the pulse going to the injector? IE, Ac or DC volts? mV??

In the old days, if the plug looked dry, the first thing we would do is squirt a bit of fuel into the mouth of the carb with an old Plochman's Mustard bottle...It would rule out a lot of things. This will narrow down the search you have exhaustedly tried (good process, by the way) by swapping out known good parts with the suspect ones. If you are having a fuel delivery problem, this will confirm. Hold the throttle wide open give it a shot of fuel, and kick it over to see if it will fire..If it does, then dies, work on finding which part of your fuel system is not cooperating....If that doesn't help, at least you will know to look elsewhere...Is their a fuel screen/filter that is plugged..? If the fuel pump is working, you should be able to disconnect the fuel line from the injector, and look for fuel to appear when you kick it over...

Make sure the tank vent tube isn't clogged.

Usually pulse is checked visually using noid light, which is basically an led or low power light bulb that flashes when engine turned over. I will see if I can find proper voltage, ect. They used to sell those lights cheap at auto parts store but doubt they will plug up to yz harness but might make one work.

Also, what about spark, visual spark at plug or tester?

Did u ever find the problem? Just curious in case i ever run into same problem.

Hi, I'm following up on this string to see if this problem was ever resolved and the bike fixed? My son has a 2010 YZ450F that has the exact same problem that is decribed with this one. I have also done the same checks as below and also purchased new ECU, fuel pump, and injector. Still won't run. Bike was running perfect. My son finished his first moto, turned it off, and when went to restart for second moto it would not start. Any ideas?

Hi guys, apologize on the delay!

What happened was my head gasket had failed and one of the layers of the gasket tore off and got wound up between my exhaust and intake valve causing it not to run. I dont have a pic of the damage on me right now but I will try to find one for you guys.

Thanks!

Hi guys, apologize on the delay!

What happened was my head gasket had failed and one of the layers of the gasket tore off and got wound up between my exhaust and intake valve causing it not to run. I dont have a pic of the damage on me right now but I will try to find one for you guys.

Thanks!

Why in the world would you change the piston at 50 hours in the first place?? These aren't Hondas

Why in the world would you change the piston at 50 hours in the first place?? These aren't Hondas

I hear ya! If I hadn't opened it up in the first place there likely wouldn't have been a problem. I was just trying to be preventative with my maintenance instead of reactive. I ride a lot of sand here which always is harder on the engine, so I was just trying to save for a mechanical failure.

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