engine starts but idle is rough keeps stalling,if you hold revs it continually backfires through air intake.Have recently renewed cambelt,it ran perfecly last season but developed the problem this year.Could it be bad fuel?
It could be bad fuel but that's easily remedied -- change it! Add some SeaFoam to clean things up. I would take a look at cam timing. It may be the belt was not properly tensioned and has jumped a cog. It happens!