FE570 2012 cold start issue

Hello, so ive bought a fe570 already with this issue. There are days when the bike just wont start or you have to spin the starter for 20+seconds with tons of backfiring and gasoline smell out the exhaust. If you pour a little amount of gas down the airbox hole she starts right away. When the bike is on, everything is fine and works as should, full power and everything. Hot starts dont seem to be an issue. Just cold starts, especially now when there 16degrees celsius. One weird thing i noticed, but i have no idea if it is normal, if you spin the engine and put your hand behind the exhaust, theres the normal air pressure wave from the exhaust stroke but right after you can feel a tiny bit of suction back in the engine. Ive setup the TPS to 0.620v and im sadly running out of ideas.
Any help would be much appreciated. Thank you!

Forgot to mention. Bike has close to 400hours, with no engine work that i know of. Everythings stock besides me doing valves. Even with this many hours the bike runs amazingly, just those pesky cold starts

And here a video of it being stone cold. I couldnt even get it start this time. After spraying brake cleaner in the airbox it started right away and was fine

rikschipp said:

Have you checked valve clearances lately? Could be riding valves or possibly carbon buildup on valve seats. With that many hours, particularly as you seem to be using it on the road, which they were never designed for, it could be using a bit of oil- the first thing to wear is the oil rings.
Also check your battery when it trying to start- if it's dying, they will drop voltage when cold, which upsets the ECU as it's not getting correct voltage, causing weak spark. It sounds a bit slow tuning over.

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Yes, ive done valves ans they are ok. No oil usage because i measured, so thats why im thinking it is an electrical issue. But the battery thing i will check. I have a second lead acid thats new. In the husaberg i have a lithium battery from the previous owner. And i bought it for a supermoto conversion but the owner before had it just as an enduro bike. It has seen tarmac for the last 20hours. Carbon buildup could be but that will wait for winter when im planning on disassembling the whole bike because of a frame paintjob. Then i will check the topend.
Thank you for the reply!

So i tried a new battery, and sadly didnt solve the problem. Starter was turning with full power, voltage wasnt going down. Still clueless

So after going for a little cruise, the bike wouldnt start atthe gas station. It wont idle at all, itll just die. It also looses power when i give more than half throttle and at full throttle it just dies as if it had no spark. Less than half throttle it goes as it should but more and it sputters, dies like it lost spark. Im totally clueless whats going on.

rikschipp said:

Could be fuel issue, more likely a filter, check them all and clean out injector- remember to open with ~5v! Read all threads re fuel filters/ injector/ fuel pump. Also if you adjusted TPS check it's clean including connectors.

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I tried everything. None of those things affected it, even new injector. But i came up with a theory why it isnt starting. The starter seems to turn quite slowly when cold and i think it is taking too much power and because of that the cdi is sending out a weak spark, therefore not starting on regular gas. With any kind of starting spray in the airbox it goes right away, and most importantly when you push start the bike, it starts perfectly even when stone cold 10degrees celsius. Im thinking the starter is bad or somekind of gear that is connected to the starter that has too much drag when cold. Not really sure how it looks ike inside.