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Recently bought a 2011 kx450, first time owning a 4-stroke, efi for that matter. The bike has a tough time starting, with the idle advancer pulled out I can kick and kick forever and it wont start, it'll even backfire after 10-20 kicks. Ive tried without the idler and the only way it starts is with a throttle blip, even then im taking my chances because it will either start, kickback, or backfire. The guy before put on a full fmf system with no re-tune as far as I know. I really don't think its the valves because it runs fine other than that. It also runs pretty damn hot after 2-3 minutes of warming up. Ive checked the plug and its brown for the most part except for a little white at the electrode. Would a full fmf system really screw with starting that much or am I missing something? 

 

Would a bad sensor cause this either?

Even after its been warmed up it will start hard again.

Edited by Walker Leonhardt

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You need to check your valve clearences.

Hard cold starting is a typical intake valve closing issue.

The fuel pump filter, the FI nozzle, all need to be clean as new to run like new.

 

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Ill be sure to check them out soon, was hopeing it was the exhaust but oh well, never checked valves before or adjusted them but from what ive read its not too hard. It even starts hard with bump starting it down a hill, if that helps comfirm that its the valves

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9 hours ago, Walker Leonhardt said:

Ill be sure to check them out soon, was hopeing it was the exhaust but oh well, never checked valves before or adjusted them but from what ive read its not too hard. It even starts hard with bump starting it down a hill, if that helps comfirm that its the valves

You cannot neglect the valve train. 

The valve faces mushroom out, and close up the clearances.  

If you shim it, you must keep an eye on it, as you should only shim it once, then the next time it gets hard to start you will need to have the head rebuilt.

Don't ignore this, as the valves can and will break. Change your timing chain and tenioner when you do the head.

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8 hours ago, Walker Leonhardt said:

By head rebuild do you mean like the top end or the actual valves themselves? Again im new to valves as ive only ever owned and worked on 2 stroke machines. 

The head is above the top end: valves etc

Don't guess! Buy a factory oem service manual and follow the recommended mantainence.........

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I always do, I just bought the bike a week ago. Guy told me it was all good to go and ready to ride, even started it in 2 kicks in front of me. Soon as I got it home it started acting up so I got screwed. Ive only started it a couple times but stopped as soon as I realized it could be the valves. Thank you for the help

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14 hours ago, Walker Leonhardt said:

I always do, I just bought the bike a week ago. Guy told me it was all good to go and ready to ride, even started it in 2 kicks in front of me. Soon as I got it home it started acting up so I got screwed. Ive only started it a couple times but stopped as soon as I realized it could be the valves. Thank you for the help

If your starting procedure is a bit off, it will be hard to start.

You must clear the cylinder if it does not start in 6 kicks or so.

Never use any throttle when starting. Zero.

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