JSH

Hi all,I purchased an edelbrock 650 with vacuum secondaries,I,ve got a 4 speed and when I kick it down it does not feel like I,ve got any secondaries at all.I,m thinking now that I should have went with maybe a holly with mechanical secondaries and if so would I get that seat of the pants pull when they kick in.Personally I,d rather have the secondaries come in when I want them to rather than by vacuum.Any thoughts on this .Thanx in advance J.S.H.

resdoggie

So I went with a Holley 650 Street HP for my 355, 4-sp. Love it!

69 Chevy

Or perhaps you won't get that seat of the pants pull when you kick in mechanical secondaries...you'll just get a great big BOG.

Vette5.5

Truth is, you can't just pull a carb out of the box, and expect it to be properly set up for your application. Carb tuning can be a lengthy process to get right, but well worth it. I always use vacuum secondary Q-Jets on the street, and when set up right, nothing will touch these. Instant throttle response everywhere, and pretty good fuel economy when cruising.

JSH

I,ve got great throttle respnse but I honestly can,t tell if the secondaries are comming in or not.

birdsmith

When properly set up a vacuum-secondary carb can feel like a rocket sled when the secondaries come in. That said, a correctly-jetted Holley double pumper is almost always a better choice for performance in a manual-transmission car simply because the driver has control over secondary actuation. As said before, though, some tuning is still almost always going to be necessary to get it running perfectly...

0Paul Ruggeri

Are you getting WOT on the primaries when your foot's to the floor? Is the choke openning all the way?

BlackC3vette

Is the edelbrock 650 the AVS model? If so, the secondaries are very adjustable.

JSH

Yes it is the AVS model so should I dump the carb and get a holly etc or play around with it. Thanx for the input guys J.S.H.

scottyp99

You're not really supposed to feel the secondaries "kick in". When you can feel the secondaries "kick in", it's because there is an ever-so-slight stumble when they first come on. people who know how to tune a carb usually can't help but be amused when they hear people talking about "...feeling the secondaries kick in!"

That being said, it's your car, and if that's what floats your boat, then who is anybody else to criticize it, right? AVS stands for Adjustable Valve Secondary. Have you tried Adjusting the Secondary Valve opening rate? Adjust them to open sooner, until you get a bog, then slowly, a tiny bit at a time, adjust the Secondary Valve to open a little later, until you have juuuuust enough of a bog to be able to feel those babies kickin' in! Let us know how it works out for ya, and good luck!


Keep the shiny side up!
Scott

BlackC3vette

Before you dump that AVS, you need to adjust the secondary opening. Edelbrock made them easy to adjust and that's why they have the AVS model. If it's a daily driver, I have found that AVS carb is actually a pretty dependable running 650.

FKING1

Ran a Holley 670 SA with vacuum secondary on a ZZ4 and now a Holley 750 double Pumper mechanical on a 383. Both performed great after much tuning with jet sizes and squirters on the DP.
As someone said above, it takes proper tuning whichever kind you run.

gingerbreadman1977

If i had just 1 dollar for every time someone with a vs carb said i dont know if my secondries are working i would be a rich man.

resdoggie

Mech'l secondaries leaves no doubt if they are working - just look down and blip the throttle. If the VS are not working, you'll probably begin to notice a lack of power above 4000 rpm no matter how hard you mash the accelerator.

lars

Actually, the Q-Jet is a mechanical secondary carb with a secondary airvalve. For a complete description of the Q-Jet secondary system, you can e-mail me for a copy of my "Q-Jet Setup" and the "Engine Vacuum Explained" papers - these papers cover the Q-Jet mechanical system and the vacuum secondary systems (only used on the Holley-based designs) in detail. Also - the original statement by the OP is incorrect: The Edelbrock 650 is not a vacuum secondary carb - it's a mechanical carb with a counterweighted airvalve secondary.

...and you're right - I've shown several times through dyno testing numbers that it's tough to beat the performance of a Q-Jet on a street-driven car:

http://forums.corvetteforum.com/c3-t...-question.html

Lars
V8FastCars@msn.com

toddalin

Lars,

Is it possible that using a smaller Holley (e.g., 650) could create a stronger signal across the venturies resulting in a fatter curve and more torque in the 3,500-4,000 range, maybe at the expense of a couple hp on the top end? My 600 dp certainly doesn't show a similar dip in that area.



Is it possible that based on their design, you can't strickly compare the two carbs of the same rated CFM?

Wouldn't an advantage of the Holley be that they offer a wider range of flow ratings than the Q-jet to better taylor the torque curve to the engine and driving style, assuming you have the time and expertise?

phclub

Scottyp, and/or Lars, I have a 70 350/300 with the Qjet, I do not have any issues with the carb but, I question if the secondaries open. Should I notice a huge kick at say 70MPH when I stomp on it, or hear a big sucking noise or surge in speed. What is the simplest way to test if the secondaries open at WOT?

wptski

Years ago, I had a '66 SS396 Chevelle. If you want to get the four barrel effect, take a 4-40 screw/nut and put it in the vacuum pull's linkage. You'll get all four all the time to compare for a short test drive.

lars

As noted, the Q-Jet is a mechanical secondary carb: If your throttle linkage is opening fully, the secondaries are opening. No, there is no "huge kick" when secondaries open correctly - just smooth transitionless acceleration. For a complete description of the Q-Jet Secondary System, and a list of issues than can prevent secondary opening, just e-mail me for a copy of my Q-Jet Setup Paper - there is a complete section regarding secondary operation, and another section devoted to the myth of non-functional secondaries.

Lars
V8FastCars@msn.com

cv67

Just fix what you got. If adjusted properly the motor only uses what it needs anyway. Should be a nice smooth transition and pull like the others say. If its a sudden lurch something isnt tuned right.