too high compression?

Thanks for that. Believe it or not, I understood everything you stated as I became a student of EGR and am no longer afraid of it nor will it automatically go into the bin when I run across one. I'm pretty certain this particular system is all venturi velocity related as the sense line is high in the carb, probably not affected by manifold vacuum. Ill have to test my theory of 'early opening equals knock' on Sunday when I get some down time. Trying to think: there is an idle, 1500 RPM and 2500 RPM load test on the rollers for CA smog. It surely gets opened at 1500 and should not be open at 2500 load test ( IIRC there is an electric engine speed sense valve that closes the vacuum source to amplifier at higher engine speeds) as they set the throttle and then load the rollers to simulate a pull. They watch to see if the motor goes under a certain RPM when loaded at a constant throttle position. I know this as I failed this one when my fuel pump was crapping out and making the carb go lean. Guy could not figure it out so he just stopped the test, took the hit (can only have a certain number of aborts in a month) and told me to go elsewhere as this truck was not testable. Pretty much if its got a carb, they will tell you to go elswehere, too much work and too high a failure rate.