flat spot

van has had timing done and valve clearance done but still get flat spots ,got a solex 34 pi ct 3 on 1600 engine with aftermarket airfilter . now when i removed air filter van run better , so is it a air mixture problem or what ?

I really don't know what else to try????? Here's the spec: Engines a new mexico 1600 AD jobby with a max of 800 miles on it. It's in my bus which is a 1968 westy. It has brand new everything; 34ICT's with wank EMPI manifolds but a decent CSP bellcrank linkage, coil, leads, condenser, points...