2010 TE450 slow cranking when starting

Hi guys, I have searched a fair bit on the net but haven't found a solution yet. My Husky has been brilliant over the years and never had an issue until now (aprox 2000miles on the clock) . When trying to start on the button it cranks slowly or just won't crank, battery is good and I have had a look at the sprag clutch and that is intact and looks in good condition. It will start if I pull the manual decompressor in it starts which is confusing me hence posting here. Has anyone has similar problems?

Valve adjustment. Think one needs to be a bit looser. Probably searchable.