Turn the idle mixtures out 1/2 a turn each, popping is usualy a sign its lean on the idle circuit

do your 40's use a spring to hold the chokes in place. this where i had problems, the chokes would move around and loose vacum/venturi effect and ruuning lean. make sure all parts are in good order.

Popping sound has also been a problem on my lower range, Is it a to lean setup ?

Very good friend of mine became the Australian offroad buggy champion [mid nineties from memory] with a very hot A15 on twin 45's fed by a mechanical fuel pump. The pump is up to the job. Saying that though, i also run a holley blue in my track car.

benny

Benny, what do you think that 450ml/minute would support power wise on a build A-series with 40's? some of our tracks have a hell of a long main straight (over 1.5km... I automaticaly went to a holley pump and holley 1-4psi regulator but I would not mind going back to mechanical because the sound of a holley makes a person mental when driving round town.

I would check the float level on both carbs, also the synchronisation between both carbs. The std mechanical pump is up to the job. .

i see...i still using the mechanical pump..do i have to use an electric pump to support my dcoes...so my tuning n jetting is not correct is it??need to make it richer a bit??

backfire /popping sound usually indicates a lean mixture condition...

maybe the fuel pumps not supplying enough fuel?????, or incorrect tune

a pop out of your carby??? could it be timing????