Base setting for throttle angle

[Pav8427]

I am setting up a 17058253 for a friend. I cant seem to find in the book or here any reference to a good base setting for when the secondary throttle plates should start to open. Is there a prefered angle that the primaries should be at when the linkage should contact or start opening the secondaries?

[Cliff Ruggles]

The opening point is determined by which linkage is being used.   Some Q-jets used on trucks and larger CID applications have linkage that provides a later opening point.....Cliff

[Pav8427]

As it sits now with pri/sec set at 90, I have 62* from  base plate. Its going on a .06 over 67 Pontiac 400 w/4sp. I'm told a 268 comp cam and 67 factory intake. The motor was built quite a few years ago,so I am guessing one of the early 268 cams. # 143 heads.  Not sure of what gears.

[Frank400]

   I play mostly with M4MV Qjets, and usually see between 43 and 48 degrees of primary travel before the secondary crack open.  Last year I rebushed a baseplate for a friend's 7042270 (1972 455 HO) and the primary traveled 42.5 degrees before the secondary cracked open.

   hope this helps,

      Frank.

[Pav8427]

Thank you. That does help. There doesnt seem to be much discussion on this subject 'out there'. Is there a proper term related to this setting/adjustment? Any search of quadrajet secondary anything most always pertains to air valve adjustment. Kind of like reading Cliffs book. The more you read it, the more you learn. (And retain)

[Cliff Ruggles]

Doubt if you'll see too much reading on the subject as for the most part the range of adjustment is very limited and there are only two options for the approximate starting point......Cliff

[Pav8427]

Cliff, since this is a somewhat tunable feature. Do you think for this application, what I have will be usable? Or would you suggest a few degrees more or less?

[Cliff Ruggles]

Having a later opening point is most advantageous for towing and possibly Marine applications with big CID engines. 

For most other applications it's really nothing to worry about. 

My daily driver (1974 Ventura) has a 455 engine in it and I have PLENTY of available throttle on the primary side for "normal" driving w/o the secondaries and my carb has the more common linkage that opens them earlier.......Cliff

[Pav8427]

Sounds good. I will leave it where its at. Thanks.

[Frank400]

In my opinion, it does not matter much on a street car.  What I mean by there is I'm either cruising in town up to maybe 40 mph, on the primaries, either cruising on the highway between let's say 55 and 70, still on the primaries, and when I go on the secondaries, I smash it to full throttle and it takes a fraction of a second for my foot to go to the floor, so it doesn't really matter if the secondaries open after 35, 45, 55, or even 60 degrees of primary travel.

   On a boat or a truck carrying heavy loads, that's an entirely different story...

     Frank.