small backfire

[dwayne]

After my van failed on Co emissions I changed all filters plugs and leads cleaned carbs and the little Carb filter. Then I warmed her up and turned in the mixture screw till it sort of misfired then out till revs picked up then half turn more out ran sweet yesterday just got to work van ran sweet again but had two small pops when doing about 75 and dropping the revs right off. Guess I need to wind it out a bit, but why does it happen? Not enough fuel to fire
properly?

[Mocki]

too lean mixture. Normally the symptoms of a air leak.

[kevtherev]

Mixture should be reset using a gas anyliser.
Like what the MOT used to check it

If your still popping then you have a leak. ..
maybe vacuum pipes

[Mocki]

zorst leak will also cause popping on over run.......

[dwayne]

Thanks Steve and kev , I guess its too lean a mixture cause that's what I was playing with lm gourmet to wind it out half a turn and see what happens on the way home