On a friends sbc he has a Holley 4 barrel with vacuum secondaries that open only about 10-15% at max pedal. What should I look for to remedy this and allow them to open to what I believe should be alot more? It's like he is running a 2 barrel. The linkage operates freely and by hand everything moves thru full closed to full open. I am not familiar with this style carb. Thank you.