C2-67 L71 and all three carburators

[Glenn Ochs]

I have a 67 L71 Vert and I have driven it very little over the two seasons of ownership. I understand the two outboard carbs come into play on firm/heavy acceleration. I likely haven't gotten to this point in the times I've had it out. Can anyone give me a first hand observation of RPM or acceleration level that would indicate the outboard carbs are operating properly? I have never had the engine over 3500rpm to date, would they be involved at that RPM?

Call me chicken, but there is too much money involved to just jump on it.All the carbs are original and appear to be mechanically proper. To recap, I am trying to find out how I would know if the 2 outboard carbs are coming into play without flat out flooring the accelerator. Thank you in advance for your comments and direction on this matter. Glenn

[William C.]

Re: C2-67 L71 and all three carburators

They will not open without flooring the carb, because it is a vacuum signal from airflow thru the center card that causes the end carbs to open. It requires full throttle to create the proper vaccum in the center carb.

[Richard S.]

Re: C2-67 L71 and all three carburators

Glenn:
Early one cool Saskatchewan morning take her out on a lonely stretch of highway and once she is warmed up....in fourth gear.... just step on it for a few seconds.....you'll know when the two vacuum operated carbs kick in because it feels like a turbo boost when they do. The revs may not need to go over 3500.....If you have never experienced the thrill of Tri-carbs you are in for one hell of a surprise and a big grin when you let up....you won't regret having lived the experience.

[Joe C.]

Re: C2-67 L71 and all three carburators

Glenn:

If you put the car on a chassis dyno, then you can safely load the engine and observe the operation of your outboard carbs under controlled conditions. As a bonus, you will also get a printout of your engine's torque/horsepower outputs vs RPM. If you intend to go to Carlisle, there is always a chassis dyno available. I think it costs about $100, not exactly sure, but if you really want a safe and reliable test, then that's the way to go.

Now, there is an alternative. As you know, the engine must be UNDER LOAD in order to cause a vacuum drop, which will open your outboard carbs. Remove the hood and the air cleaner. Then have a friend lash you to the right fender with some good, stout rope (13/16" manila hemp is optimal). Have your friend, with valid driver's license drive the car, while you observe. Have him get to about 80 MPH, then mash the throttle. At this point you should observe the outboard carbs opening.

Joe

[Clem Z.]

go to www.vetteheads.com

and open tech tips for Q&A all about the 3X2 carb setup and if it is working. i do not want to retype,as i just use 2 fingers, it all over again.

[Rich G.]

Re: C2-67 L71 and all three carburators

What evryone says is true. I have a 68 L71. It does feel like a turbo when you get the end carbs open. 3500 rpm and WOT. I have repop relines and it does get scary. Just today I had the tires spin when I got on it in first gear after a normal start when it hit about 5000 rpm. The good news is you can always take your foot off the gas. Mine has a 4:11 rear.

The fourth gear test someone described is probably the safest other than the dyno. You'll know when they come in.

Have fun!

And if you do tie yourself to the fender, please post a picture.

Rich Giannotti

[Ralph E.]

Re: C2-67 L71 and all three carburators

Glenn,
Beware! Make sure no one in front of you. It is a great awesome feeling when they kick in. Because you haven't used them there will be a slight delay, then a blast. When you chicken out and let your foot off the gas there will be a lag time as the vacuum diminishes.
Have fun!!!

[Frank H.]

Re: C2-67 L71 and all three carburators

Or put a screw and nut in the slide slot in the throttle linkage to pull the end carbs,and fill the tank and go drive it.thats the best,gas gauge drops quickly.