Most common cause of secondaries not opening

[TA301]

E4ME carb with MCS. Secondaries don't open under load/acceleration. Is the butterfly valves tension set screw the culprit? I don't like that my TA is acting as if it has 2 barrels.

[b_hill_86]

I’m no expert and going from memory but the set screw would be one thing along with the vacuum brake/pull-off.

[Wallington]

Don't test them by reving in garage, they will never open. Only open under load when driving, seems you know that but it commonly comes up. Could be adjustment like Brian mentioned based on the choke and secondary pull-offs. The small arm catches the secondaries rod and prevents them opening until choke is fully off, like starting car and roaring down road when cold, secondaries are prevented from opening. What's MCS? I'm not sure any electrical settings prevent it in the same way, I'm not familiar with the computer versions. Everything runs off vacuum, if something blocked somewhere it won't get the signal that the pedal is planted and the vacuum has dropped. But I'd imagine the secondary pull-off would know.

[Oldsschool79]

Seems to be a common problem. Everyone had all the important checks named. Don't overlook the electric choke. There is a lockout until the choke stove heats.  I had a choke stove actually melt the tab inside and it only moved the primary butterfly, not the lock out.   
Hope this helped. 

[Wallington]

As mentioned, this pic shows the small arm that fouls the secondaries until the choke is fully off, then it drops away and they 'unlock' and able to open if needed.

https://www.hotrodders.com/attachments/hppp_0311_06_z-rochester_quadrajet_carburetor-removed_choke_spring-jpg.276849/

[b_hill_86]

I was thinking of this and recalled a small issue I had that didn’t fully prevent the flaps from opening but I guess it could and in my case it caused them to hang up a bit. What I’m referring to is a small rod that the tension spring rides on. Mine developed a small indentation for lack of a better word that caused the spring to hang up. When I had the carb apart I had to polish that little rod to get the spring to move smoothly.

[TA301]

Thank you for the answers. I made adjustments to the electric choke. The lockout rod would not release with the engine hot. I will let you guys know when I test drive the car.