Ya tighten the sec. spring down it will open later,
of course you can use a wire to tie it closed if
you dont want it opening up.
There also is a bendable tab by the throttle linkage that
can be bent to open the sec. sooner or later (careful not to over bend),
this tab is a manual linkage adjustment (not a vacuum adjustment)
and can make the sec. open at a lower or higher rpm.
In fact you can use a tach to have them open in your desired power curve.
Sure seems like one of the most important areas of the Q-jst is tunning the secondaries,
with rods, hangers, air flaps, springs, pull off, accelerator pump, there is a lot to balance.