Acceleration and Deceleration Tests when looking to buy

[Stallion]

I was just reading in my Vette book that when looking at a particular Vette, there are steps and things that you must look for and notice when driving/looking the Vette over. And, I just have a couple of questions as to what some of these tests mean.

In a Ten-Mile Road Test, Newton says that there are things to watch out for and take note of. Two of the tests are Acceleration and Deceleration of the Vette.
In the Acceleration test, he says to make sure there are "no misfires or stumbles when secondaries open". What exactly does this mean? What performance of the Vette is he referring to? What are "secondaries"?

In the Deceleration test, he says to make sure there are "no backfires". Again, what does this mean?

Thanks!

TR

 

[Stallion]

Anybody?

Thanks!

TR

 

[Baldie88]

For those of us old farts that remember 2 and 4 barrel carburators, secondaries are when the "second" set of butterflies opened up. You would normally only run on 2 of the 4 barrels of the carb but when you put your foot into it, these secondaries would open up, giving you more gas/air mixture. You want to have a smooth application of power when these open up and no hesitation. Learned this the hard way when I floored a 69GTO from about 40mph and it got squirrelly on me.

Backfires on the otherhand are when the gas/air mixture "burps" up through the carb. You also get a corresponding sound like a shotgun coming from your tailpipe. Again, not a good condition and an easy way to blow out your muffler.

I'm sure someone has a more technical explanation but this is the "down and dirty" one.

 

[Stallion]

So the carbs don't use their "full capacity barrels" in normal running, but when needed, then open up more? Interesting.

In the backfire, what exactly do you mean by "burps" up through the carb? Wouldnt' that create an explotion if ignited?

Thanks!

TR

 

[Mad-Mic]

yes sometimes. it's called an intake backfire. usually just a quick puff. this usually happens when the car is cold and or just really ragged out in need of a very bad tune up.

 

[Evolution1980]

Basically, on the acceleration test, that means STOMP THE PEDAL TO THE FLOOR! If the car hesitates or sounds like it's about to putter out and stall, something is out of whack...likely the carb needs to be adjusted or cleaned. Do this when the car is fully warmed up, like after 8 minutes of driving your 10 minute test. Pretty much any carburated car will putter and sometimes stall if you floor it when the engine is cold. ("Flooding your engine.")

Talking about backfiring, well, let's just say you'll probably know it if you hear it. In our cars, it sounds like a really really loud firecracker! It makes you turn around when you hear it

A word about the "acceleration" test. If you are test driving a vette, do everyone a favor and don't do it. Since you are just getting your license, you don't know what to expect nor how to handle it should it accelerate just fine. Also, if you do that, I'm sure the buyer would likely kick you out of the car right then and there and tell you to walk home! I wouldn't say either test is a critical test. If anything, the deceleration test is better for checking brake condition. But again, this is all completely new for you. You really aren't going to know what to look for drivability-wise even if someone told you what to look for. You won't know the "feel" of the car or it's handling characteristics, and especially if you are trying to compare it relative to any other car you may have experience driving (such as mom's Camry or Joe's Escort).

My advice is to take someone older that knows cars (not any of your school friends). By older (relative to you being 16), I mean late 20's on up or at least someone that has a few years of Corvette driving under their belt.

 

[Stallion]

Absolutely, I won't go alone. My dad would probably come with me to look at Vettes. And, I know what you mean about the acceleration test. Thanks!

TR