Vacuum Secondary vs Mechanical Secondary Carburetors - Summit Racing Quick Flicks

Learn the basic differences between mechanical secondaries and vacuum secondaries on carburetors. This video includes a brief description of how the secondaries operate and insights as to which style is right for your vehicle.

[SummitRacing]

There are many things that can cause an idle to smell rich, as well as many things that can cause stumbles and hesitations. Please give us a call on the technical hotline and we can discuss the matter further! 1-330-630-0240 Thanks for watching!

[SummitRacing]

Let us know if you have any questions. We would be happy to help!

[SummitRacing]

A vacuum secondary carburetor opens the secondary air valves just a little slower than a manual secondary carburetor. Sometimes this is called a “progressive” opening. This provides a smoother transition of power when accelerating away from a stop. Please let us know if you have any additional questions. Thanks for watching!

[SummitRacing]

You should not because with any carb, tuning is required! You may have to install a slower secondary accelerator pump cam or a smaller secondary squirter nozzle. Tuning time will tell! :) Thanks for watching.

[colinr]

I’m glad I found this. Building a 84’ 5.0 foxbody. Last and final thing for me to do was to figure out what carburetor I needed. Good to know I need a mechanical secondary carb. 😁

[SummitRacing]

In this case, due to the fact it is supercharged and mainly a drag application, the suggestion would be a Holly Supercharger specific carburetor. The part # HLY-0-80572S is a great choice here!

[knightridersofgreece]

am i gonna have a problem if i use a mechanical secondaries carb on a automatic transmission car!what difference will i see in the performance?

[akassasin]

What if i have a street car that i want to run 8 second quester miles. that is an automatic and also a full forward manual.

[SummitRacing]

With the accelerator pump at the max setting, the next step would be the Edelbrock part # 1475 Accelerator pump nozzles. This will allow more fuel out of the accelerator pump right off idle that should take away any off idle hesitations or stumbles!

[MrChargoholic]

I've done this by ear/driving and the overall driving is real good almost as an efi but what's bothering me is the rough idle and lack of "woff" from idle...
Acc pump is set at max of the 3 settings.
Lean idle circuit?

[avatarrestorations]

What about the 450cfm mechanicle secondary carbs with only a single pump shot, the idea being that vacuum draws from the booster as in a vac sec..what happens when the pedal gets mashed opening the rear secondarys but with no pump shot to fill that hole until it draws..these mechanicle secondary carbs are sold for tunnelrams, with a plenium the vacume signal is lower. Question: Can you do a vid on these 450cfm carbs and explain why you then recomend these carbs? In theory they seam like the worst possible combination?? ( unless its in a light tbucket that wont lean bog)

[gravityflyer]

What about the inverse of the situations you describe in the video? Specifically, what if someone has a manual transmission for street application, or has an automatic transmission for racing application? Is the recommended secondary then contingent upon other considerations, i.e. engine design?

[Whatthefuckisgoingon]

u guys read my mind cuz i was lookin for this yesterday on the net just to get a refresh course on it but no articles much...

[MrChargoholic]

I've been
My idle mixture is a bit fat, can this make the idle stumble and the kick down hesitate?

[MrChargoholic]

My 1407 edelbrock carb does not respond like I want on from idle flick'n on the throttle.
Does a mechanical secondary solve this?
My engine is a 5, 7 HEMI with a bigger xfi 273 comp cam and msd6 hemi engine controller.

[davidrowland]

I got a me mechanical carb with a automatic trans..having trouble with secondaries opening when i go to wot

[SummitRacing]

Thank you! Please let us know if you have any additional questions. Good luck!

[SummitRacing]

There are actually many things to consider in the proper choice of a carburetor. Engine design would be one factor as you start to reach higher effort (Race) type motors. For the average street driver, the CFM calculator on our website will do the trick just fine with proper tuning. As a general rule of thumb, street driven automatics are better off with a vacuum secondary; and manual shift car with a mechanical secondary.

[reweydewy]

Why is a vacum secondary more for Auto Transmissions? I have a slight idea why but not sure enough to type it here. Can anybody shed some light for me? I would appreciate it. I wish there was a little more info in the vid!

[dennisbryan]

doing a carb swap on my lt1 it is a six speed car
I think I'm going with a holley 4150 with mechanical secondaries