Can any one help me ?

my van was really bad and had top end rattle, so changed cam and started to run better, then i think it sliped a tooth or 2 cos start to run shite again, last night, sorted timing out again and it fired up but over reving and couldnt controll it, could only controll it by screwin a screw on meatering head,
went back out tonight to fire it up and wouldnt fire ?
theres fuel getting through and theres a spark?
Olny thing is which its never done b4, the Flap on the meatering head is flaping (opening and closing fast) when i turn it over??

any ideas cheers,

ERST motor by the way