Need more Power and Speed
 

Hey guys!

Here again with another question. I've got a 1969 C3 5.7 L 350 engine. Got her about a year ago, total car newby, but thanks mostly to you guys I am learning.

The car is my daily driver. I stick to neighborhood streets, low speed, just a few miles distance. So I rarely get above 60 mph. But when I do go on the freeway, or when I need a quick boost of power, the car just isn't performing.

The absolute max I can do is 80 MPH on the freeway. And it takes a loooooong time to get going that fast. The car is very low power and very gradual in building up speed. I need tips on how to help the car's performance! I have attached pics of my engine setup and carb.

https://cimg2.ibsrv.net/gimg/www.cor...663a0fabe9.jpg

https://cimg3.ibsrv.net/gimg/www.cor...86bd2a271c.jpg

https://cimg5.ibsrv.net/gimg/www.cor...3a0f2d8874.jpg

Now a couple things to note. I suspect I have a cylinder(s) not working, and am doing a compression test this weekend. Another potential problem is the little edelbrock carb the previous owner put on it. I have not heard great things about those carbs, and need suggestions on what I should replace it with. Also, I think there is something up with my gas pedal or the throttle. The pedal virtually doesn't move when I press it, because it's already so pushed-in. From its starting position to the floorboard, there's maybr an inch or half inch of movement. So when I want to give the car any gas at all, I have to push the pedal all the way down.

So what do the experts think? How can I improve this engine and give her more power? Any and all suggestions are welcome, again, I'm still learning.

Bonus question: I have always been a bit confoundd by the fact my car is an automatic, but has 1st, 2nd, and 3rd gear like a manual. I always just put it in 3rd as my defacto "Drive". But is this the way the car is intended to be driven? Is this a normal setup for a 69?

https://cimg0.ibsrv.net/gimg/www.cor...a9c573e5df.jpg

As always, thank you all SO much.
God Bless!

Do the easy things first. Sounds like a throttle linkage problem, yes a compression test is easy, do that, check timing, look for vacuum leaks. if everything checks out go after the carburetor. Carbs are really famous for being bubba'd up, sometimes really bad. Read threads on carbs, you will learn a lot. Lars is the expert on these. PS Have fun with your Corvette!

My 76 L48 was an absolute dog until I installed a pair of late 1990's vortec heads along with a thin head gasket and a set of Hooker headers. I had to change the intake manifold to accommodate the vortec heads. In the end it was well worth the effort.

Have you tuned the car?

This is most likely your problem. Check to see how far the throttle blades are opening.

I really don't know what you're trying to say here.

OP
I think I understand your auto transmission question. Yes, "3" is defacto "Drive."

Others, this ain't the L48 we often address.

This pre-71 actually came with snappy compression ratio ... supposedly a little more than 10:1.

As others said, check/remedy throttle pedal ... linkage ... cabling.

Strongly suggest OP get an owner's manual for his 1969 ... widely available as original or reprint.

When you put it in the "3" position it allows the gearbox to use all 3 gears as it needs to.

If you were to put the lever next to the "2" you have locked the 3rd gear out which means it can only use 1st or 2nd gear.

Leaving it next to the 1 means it will stay in first gear only.

As for the throttle opening, with the engine turned off , take the airfilter lid off and get someone to sit in the car and push the pedal to the floor while you see how far the "blades" open , they should be vertical as in giving the least resistance to air rushing in. If your not sure take a pic of the results and post it back here

I agree with others on the throttle not going wide open. A easy test is to look down the carb and operate the linkage so you know what it looks like when its wide open. Then have a friend step down on the pedal to see if its opening all the way. The early C3s pedal linkage is kinda weak and bends, just don't try to straighten it in the car because there is a plastic piece that will break, remove the pedal assembly first for straightening. T

Start by adjusting the gas pedal so that the carb opens 100%.
See Lars post at # 11 here:

https://www.corvetteforum.com/forums...-throttle.html

EXCELLENT reference. :iagree:

Look under the gas pedal for folded up rug or may be a big fat layer of Dyna mat underneath the carpets it's limiting your gas pedal travel.

I had a simple tune up done right after I got it by a mechanic. What all does a "tune up" entail? I know I got new spark plugs and I think a few other problems fixed. Just want to know what else I could do.

This is great guys, thanks! Will do that this weekend. I will post pics, but I am almost certain the carb flaps don't get vertical (all the way open) when the throttle is all the way pushed in!

If this is the case, is it an easy fix I can do myself? New throttle cable and such?

OP
Read the posts above, especially #9

go to the link below and and to post #11 by Lars ... Read Lars' instructions and follow them.

https://www.corvetteforum.com/forums...-throttle.html

Couple questions from the instructions you guys have guided me to.

"With a helper in the car and with the engine “off,” have the helper fully depress the gas pedal (with the engine hot and the choke wide open to assure that the lockout lever is disengaged). Observe the carb on the driver’s side and see if the secondary throttle moves to the wide open position: You can grab the throttle lever once the assistant has the pedal to the floor and see if you can move it further. If the gas pedal does not fully open the secondary throttle, you have one of several methods to fix this"

1. So the choke is a device that literally chokes off air from the carb, but only when it's starting right? By simply warming up the engine, will it open up?

2. Need to know how to tell if choke is all the way open. Bonus question: if the choke is the section I have circled below, then what are the 4 metal flaps within the carb called that activate when the throttle is pulled?

https://cimg7.ibsrv.net/gimg/www.cor...89dcce2916.jpg
(The choke is the circled part, correct?)

3. What's a lockout lever?

4. What's the difference between the throttle and secondary throttle?

1. No Yes
2. Butterflies
3. It prevents the secondaries from opening before engine is warmed up.
4. Thottle is simply providing necessary fuel/air mixture to increase the engines rpm's and Secondary throttle is for greatly enriching the mixture for maximum engine rpm's.

I would do the following

1. tuneup....., plugs wires, cap and rotor. If you dont know how to deal with the dwell, you should upgrade to a HEI or pulsed pickup like pertronix or lectric limited or you'll have to look it up
2. timing
3. check the throttle throw using a zip tie on the throttle cable. my guess is your pedal is bent like so many of ours. Like everyone states you may not be getting your secondaires to open. On the edelbrock, the upper rear door is an air flap, its an on demand open by the air flowing through it
4. make sure your choke is connected to a pull cable or has the electric choke. From your pic it looks manual and you need to wire it so it stays open if you are in a warm state
5. tune your carb, luckily edelbrocks are easy, just download the manual for your carb.
6. check your rear end ratio to see what it is. If its above 3.55:1 ( lower numbers) it will feel like a dog off the line with an automatic.

Check to make sure the pedal bolt is tightened to the cross rod of the linkage, (see yellow arrow)
If this is loose, the D-shape of the rod and clamp won't engage tightly, and you'll get a pedal that doesn't throw the linkage fully when depressed to the floor.
All the other recommendations should also be followed, as they are typical maintenance items that a tired engine should receive on a regular basis. And yours looks like it could use that type of TLC for you as its new owner and caretaker!
My pointer was meant to be a potential quick fix that I also experienced.
Good luck in your journey!

https://cimg6.ibsrv.net/gimg/www.cor...57e17a1571.png

Hey guys!

So I went to work on the throttle this past weekend using the instructions provided here. Here are my results. I'd love to get your thoughts!

Here is an overhead view of my carb, before I did any work.

https://cimg3.ibsrv.net/gimg/www.cor...5b794779e0.jpg

And attached is a video of me pressing the gas all the way down. As you can see, the throttle doesn't move much, the primary butterflies open just a bit, and the secondaries don't open at all. Keep in mind, my foot is ALL THE WAY down.

I proceeded to do a couple of simple things. I cut a section out of my floor mat to provide space for the pedal (one of the "25 HP tricks"). Then I bent the pedal off the floor, being careful not to break any of the plastic parts. I could tell it made a big difference. Lots more space for the pedal to go!

BEFORE:

https://cimg4.ibsrv.net/gimg/www.cor...bdf1fa67e8.jpg


AFTER:


https://cimg7.ibsrv.net/gimg/www.cor...88e480214d.jpg