2011 YZ450F - Only bump starts

Having an issue trying to diagnose new to me 2011.

I have a 2010 which has now issues.

 

When I bought the 2011, went through and replaced timing chain. Put it back together and kick started ok. Sat through winter, now it will only bump start. I had both bikes side by side today doing some work. Swapped coils as I had an issue with my 2010 couple of years ago. Still no luck. Bump only. When it starts, it runs well. Stop and immediately try to kick - no go.

 

Checked timing again, spot on.

 

A little stumped as to what to look at next.

 

BTW  no codes with programmer. Bike has 60 hrs on it.

 

Thanks

 

kjh

 

 

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Is the valve clearance correct?

Valve clearances were all in spec. I checked when I changes the chain.

Plugged injector or fuel filter?

Edited by billygildark5007

I cleaned my injector with the same symptoms that you have and it made it better. Still need to buy one

Thanks for input. I will check injector this weekend. Look at fuel flow.

Clean all the electrical connections also as that's all it took for mine when it was having problems.

Update. Got a chance to look at it today. Cleaned all connectors. Rechecked valve clearances.

Checked out the injector. Put a rag under the throttle body, it did get wet with fuel after a few pushes on the kick starter. Put in injector cleaner and ran it around the yard and let it idle.

 

No matter what - still no kick start. Only starts by bumping.

 

A little frustrated.

 

What am I missing?

 

thanks

kjh

Did you check the spark when using the kick start by pulling the plug?

What it sounds like to me is a check valve problem in the fuel pump.  The injector needs fuel pressure at about 45 psi to fire.  That's why it frequently takes more than one kick to start them.  Fuel pressure may not be high enough yet when the injector pulse comes, but gets built up by the end of the kick.  Then the next kick the pressure is high enough, and it starts.

 

Something has to hold the pressure you raised on the first kick, or it won't start on the second one, either.  That's a simple one-way valve called a check valve.  If, as I am almost certain, the system has one, it's in the fuel pump assembly.  You can test it if you can get a pressure gauge connected to the thing somehow.  Pressure should rise on the first kick and stay elevated for at least a minute.

If you think its fuel, shoot some starting fluid in it and see in it starts no need to hook up a gauge to the fuel pump yet. 

Update.

Swapped fuel tank/pump from my 2010. No difference.

Took out the injector - cleaned.

Cleaned stator connectors

Check plug -spark ok

 

Still only bump starts - no kick.

When started - runs well.

 

Pushed to back for garage for day.

 

Any suggestions what to look at next.

 

Swap ECU?

This morning swapped ECUs but still no difference.

leak down test ? had an older bike that would not start by kicking it because of low compression but after a good push down the trail it would fire. 

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