77-4speed

Hey all,

I am having some difficulty with my 77 L-82 4-speed. I am having 2 problems:

1)a hard time starting when cold and
2)a big off-idle hesitation followed by a backfire through the carb.

My setup consists of:
Some aftermarket cam (no idea on it's specs, previous owner installed and forgot)
Weiand intake (don't recall model, previous owner installed)
Hooker headers
New HEI distributor with new vacuum advance
New MSD Coil
New Taylor Wires
New Plugs
Edlebrock 600CFM carb with electric choke and new in-line fuel filter
Open-air style air filter
Everything else pertinent is original


Regarding the difficulty in starting the car. When it's cold, I turn the ignition to "on" then pump the accelerator once all the way to the floor and release, then push down about 1/4 and hold. Then I crank in 5 second bursts and the car usually starts after the 4th attempt. I have to hold the accelerator down about 1/4 for a minute or 2 or the car will die. After a couple minutes I can release the accelerator and it idles at about 1300rpm. Once warmed up, I can fire the car up instantly with no touching of the accelerator.

Regarding the hesitation. If I punch it from less than 2500 rpms the car lurches and backfire's through the carb. If I punch it at 2500 or higher, it goes along just fine.

My timing is 12 degrees at idle with vacuum advance disconnected and about 28 at 3000 rpm. I am running the softest springs that came with my re-curve kit but can't seem to hit 36 degrees. I currently have the vacuum advance connected to manifold vacuum.

Any help in getting this car running smooth would be great! Even a recommendation for a competent shop around Houston would help. I've been less than thrilled with my local mechanic (who threw out my quadrajet carb because he thought I wouldn't want it )

Thanks,

Russell

redwingvette

Check the accelerator pump. It should squirt gas down the carb when you step on the gas pedal. You can check it with the engine off. Take off the air cleaner and rotate the throttle to wide open. Also check the choke plates to see if they are opening up once the motor starts. They should close when you first start the motor, Then they should open a little once the motor is running. They should open the rest of the way once the motor warms up.

77-4speed

Will double check that tonight.

olescarb

first i would make the vacuum advance ported because if it is a automatic trans the vacuum will drop when you put it in gear and thus it will lose advance at idle

on the carb if it is a #1406 switch the metering rods from 75/47 to 71/47 the accelerator pump on the edelbrok carbs is really weak you can use a pump from a 800 cfm edelbrock or we are making a custom pump with a stronger duration spring. the carbs also have a lean stumble off idle / on light acceleration that we can or you can cure by modifing the "economiser restriction "

if you have access to a exhaust gas analyzer or a wide band air/fuel ratio meter you can check the air/fuel mixture but the air pump (if any) must be disabled and the resdings taken in front of any catalitic converter. the Edelbrock carbs have a lazy pump and lean off idle problem in my experiance that becomes worse if you have a air-gap or single plane manifold. once tuned for the correct air/fuel mixture they are good carbs but for most everyday driving nothing beats a well tuned q-jet. for race engine use i am a mighty demon fan

77-4speed

Olescarb,

The vehicle is actually a 4-speed so there shouldn't be a problem losing vacuum.

I'll double check the carb number as well when I get home.

lars

Hesitation with backfire through the carb is a lean condition. Richen it up after verifying that the accel pump is working.

comp

and let us know

copter

I'm going to have to on this one because my 71Z/28 does the same exact thing.I'm running a Holley 650 brand new.

Avette4me

at idle, a ported source is not creating vaccume anyway..i've been hooked non-ported for years and get good results..

i agree with lars on this one.. Lars 101, richen it (he's told me that about, 56,016 times)

Kilroy1024

I just played with this myself, mine would quit after starting, and then hesitate badly when cold.

I took the air cleaner off, started the car, and then adjusted the choke by hand to find the right spot for running cold. If it started to stall, iclosed it up til it came back. Then I shut off the car and adjusted the choke thermostat spring until it was closed a little more than that. (The air drawn into the carb when its running opens up the choke a little more) It took a few times, but now its running much better.


I find that hard to believe that the mechanic would throw out your carb. Couldn't he send that back to a rebuild shop for cash?

olescarb

a holley hesiation on acceleration cure is a "pink" cam .031 squirter and 2 5/32 flat washers spacing the duration spring on the pump arm. (a old Barry Grant trick he now uses a stronger pump arm spring on all the demon carbs)

you are just guessing if you throw more jet at it, check the fuel mixture with the proper tools such as the Innovate LM-1 air/fuel meter or a exhaust gas analyzer unless you don't care about gas mileage, drivabilty or just doing it right

Jimi Lane

Sounds like something isn't sealing, leaning out, or timing advance.

If you have the vacuum advance connected to manifold vacuum, when you punch it, it will take all the vacuum timing out due to zero manifold pressure. I would just disconnect the vacuum advance line and see if there is a difference. Vacuum advance should be connected to ported vacuum, not manifold vacuum. Connect to a port that doesn't have vacuum at idle. If the (ported) port has vacuum at idle, there is trash in the carb.

Accelerator pump draining, or not enough of a shot.

Intake not sealed good. Spray a lot of carb cleaner on the intake and head mating surface. See if smoke comes out the exhaust. Takes a few seconds.

Spray carb cleaner in the valve cover, see if smoke comes out the exhaust. Takes a few seconds too.

Just some ideas...I sometime try to find out what it's not instead of what it is.

Jim

Avette4me

well then, i wonder why the make all the others?

really...

mdarney

I just finished my cam install and had one of the problems you are describing. I would put your timing at 8 degrees and check for vacuum leaks. I had a leak in my manifold, after retightening the manifold it went away. This is just a thought. My car would not backfire at full throttle but was very hard starting cold and would not idle till warm. Also you may be getting to much advance at idle with the soft springs I tried those and found that I was getting advance at idle causing a miss. You might try different springs.
-Mark

Richard454

My bet is it's your timing not advanced (advancing) enough. Try this first before messing w/ your carb.

Richard

Fubba

It's definitely the carb. Same thing happened with me. The more crap I did to my motor the worse it got lol. I changed the springs to the tallest ones or the pink springs. I have really low vacuum...like 12". Anyway, definitely look at the chart in the manual for your carb and go up one setting. I can't remember the number on the thing, but all you have to change is the rods and it takes like 5 minutes. This was the first time I had ever taken it apart, and it was easy. Try that and see what happens. Also, adjust your idle screws so that it pulls the most vacuum from where you have your vacuum advance hooked up. Make sure you turn each screw the same amount so that they are screwed out the same. Turn one in counting the number of turns, then turn each one back out that same number. After you turn each one about a quarter of a turn, lower the idle speed to where you want it. Keep doing this until the maximum amount of vacuum is there. I used to have a great article on it, but now I can't find it. If you need anymore help just let me know.

mstock

If you have been running the vac off the manifold, it is possible that your timing advance is now stuck in one spot, and not functioning at all. The guy who rebuilt my motor messed up there, and I experienced similar problems to yours. Just a thought.

olescarb

yup modern technology works to read air/fuel mixtures. unless you are running race gas you may need to tune a engine designed for real gas that to run on the "gas" you buy today. try a tank of race fuel and see how diferent your car runs. Barry Grant is selling a lot of carbs because he understands modern technology and how to tune a carb to run on the gasoline that is sold at the pump

Avette4me

i suppose there is some merit to that, but ole barry and i will just have to agree to disagree..i think you can still tune an old carb car without much more than a good timing light, some good hand tools, a few skinned knuckles, and a 12 pack...

fwiw, pink isn't always the answer on a lean holly...

olescarb

pink is not always the answer on a holley but that and a stronger spring is a place to start on accelerator problems. we have gone up as much as 6 jet sizes on the holley street avenger carbs to just get the air/fuel mixture close so it takes time.
but how do you jet a carb without reading the exhaust gas since this new stuff they sell for gasoline does not leave any color on a spark plug till it is too rich. trial and error costs far too much time