Cycle from Fukuoka to Kyoto

I am arriving at Fukuoka on the 28th of June and I am thinking to cycle and camp from Fukuoka to Kyoto. But is the weater good for cycling and camping in July? And is it possible to buy a second hand bike in Fukuoka as a foreigner? Any other advices? Thank you!

Are you used to high humidity with summer temperature? You are talking about something like 650 km, so maybe 7 days or so assuming you go 100km per day? In this heat, I would not recommend it. It is the rainy season now (and into July), so the temperature can be high and the humidity is extremely high. It feels like moving through water when we go outside.

Also you need to do some research beforehand if you want to camp, looking for camping grounds along the way.

1-A)
http://www.jma.go.jp/en/week/
http://www.jma.go.jp/en/yoho/
1-B)
Recommend legal camp sites.
http://www.autocamp.or.jp/?page_id=5
But very rural area possible mostly. (Ask locals or Police station/box)

2)
Buying possible but not so easy to find good one for long touring.(Ask locals)
used/2nd hand : 中古(ちゅうこ)/chuu-ko
cycle/bike : 自転車(じてんしゃ)/ji-ten-sya

3)
Traffic law/rules :
http://jpninfo.com/24112
http://expatsguide.jp/travel-transportation/on-the-road/riding-a-bicyc...
https://www.youtube.com/watch?v=MurfsFk8CZ4

Only "Kanmon kaikyo" tunnel need 20Y(20円).
https://en.wikipedia.org/wiki/Kanmon_Straits
http://voyapon.com/kanmon-tunnel-honshu-kyushu/
http://www.geocities.jp/desert9130/DSCF3223.JPG

4)
If enough time.
http://www.go-shimanami.jp/global/english/

A secondhand bike? You're not prepared for a trip that long with a decent bike? I would not recommend attempting such a thing without planning it out first.