Hey guys, so a few questions lets start with my 76 stock engine running lean. It has a pop when you let off the gas quickly not much of one but its there. I did have the four barrel rebuilt but it did not work. He did say lots of moving around of lines has occurred over the years not really sure what he was talking about but he said we might need to replace the distributor. I want to redo the top anyway should I just replace the carb and distributor if so what are your thoughts on that. I am not sure of what has been done over the years but it does has hedden heads/exhaust and a mild cam.

I am sitting on a 396/375 complete engine from a 69 camero SS which needs work but overall in solid shape. (barn find from a neighbor)I really do not want to go that big HP wise but can those heads/manifold work on the 350 block. The head number is 3964981 or just sell this engine and just use the money to work on top.

 

The 396 is a big block so it wont work on the 350 block. You should be able to get good money for it if you dont want to use it....I would personally but I understand the hassle of changing to a big block.
As to your mechanic he may be talking about vacuum lines and smog parts. If you arent in CA and can remove all the smog crap I would, it would make your motor run better and would be easier to work on. Is your carb a quadrajet. If so you need to send it to Lars. Most folks dont know how to work on one. If you are doing it yourself getting the How to book by Cliff Ruggles is a huge help. I dont know why you need to replace the distributor either. If its an HEI you can just replace the coil or rebuild all the bushings and the gear.

Can you post pics of the carb and the distibutor as well as a whole engine pic

 

Here are some pictures with a few more questions. What does that green thing do that is inside the air cleaner. I notice one of hoses plugs into bottom but looks like it is really a plug. The silver tube coming out of air cleaner is that just for extra air. And the idle is about 6 is that to low.

 

That looks like a completely stock motor.

The silver thin metal tube is a hot air duct for aiding in cold strarts. It brings air up from th eexhaust manifold to warm up the intake air.

The green thing is a vacuum valve heat sensor for the front air door flap.It is related to the silver hose. If its not plugged in you will have a vacuum leak




When you say the idle is about 6 do you men 600 rpm? yes that is too low it should be atleasst 750rpm. Your stock timing should be at 8 but that is for emmissions. IT would be better up near 14 but you should go through the whole timing procedure that Lars pubishes.

 

The popping when you let of the gas could be as simple as moving the vacuum advance from ported vacuum (stock) to manifold vacuum (Lars-method). But you should get his full instructions and do the entire timing procedure.

Do you have a timing light? If your timing is jumpy, you may need to rebuild or replace your distributor (take a look under the cap for "rust" that makes the timing weights stick). Otherwise, start by looking for vacuum leaks.

 

Thank you and yess its 600 but once it is warm it goes up to 10 and holds. It is a bear to start cold with a lot of pumping and cranking. To me it sounds like the choke is not engaging when cold. As far as the low idle I know with some cars there is a screw you can turn a little to increase it a bit. Does this carb have that.

 

Yes it has a choke and 2 different idle set screws. The low idle set screw for when it is warm is on the drivers side. The high idle for the choke is on the passsenger side. You should block all the unplugged vacuum hoses before you try to adjust anything. When its cold pump it a few times then try and start it. If it doesnt start adjust the choke so the choke flap shuts then pump it once to set the high idle cam and try again. Once it starts turn the high idle screw to get it up to 1200 or 1500 rpm. Once its warm pump the pedal once and the high idle cam will come down. Once it moves out of the way adjust the low idle screw so it comes down to 750 rpm

 

If it doesn't start adjust the choke so the choke flap shuts then pump it once to set the high idle cam and try again.

Meaning adjust the choke by turning the high idle screw or is there a separate way to adjust the choke

Thank you for the help.

 

The choke is adjusted by moving the big black plastic disc. You loosen the screws and rotate it and you will see the lever move. It doesnt take much and there is a few lines on the plastic so you can see where it was before you adjust it.

 

Heres a youtube video I found that should get you pointed in the right direction. Yours may be different But it will give you the idea

 

Heres some more links

https://www.youtube.com/results?sear...rburetor+choke

 

That video was great thank you. The popping when I let of the gas quickly is that lean or rich and would that have anything to do with the choke and cold starts. I did not see any vacuum leaks. I did get the warm idle up to 750 with just a slight turn so that is better.

 

I had a lot of popping when mine ws runiing rich. You would be able to smell it

 

I do so I am going to set the choke back a line to lean. It is set right in the middle now and see if that helps.

 

Once the car is warm the choke is off and wont effect how it runs. If its running rich or lean after getting warm make sure the choke is full y open. If it is then you need to replace rods or jets inside the carburator

 

Popping in the exhaust is almost always indicative of a lean condition. There are several ways to correct this without doing jet or rod changes, but the carb must be disassembled.

Lars

 

So I thinking just buy a new carb. I can get it rebuilt for about 150 but I get a new one for like 250 any thoughts on a electric choke. I want to do some top end work anyway.

 

And thank you for your time, I just noticed it was you. I have read and learned a lot from your work. Everyone here is so helpfuIl you all just need to move to North Carolina lol just brought my first Corvette about two months ago (my wife finally said ok lol). It is a 76 but the idle, rough cold start and the popping has been an issue. Our local guy tried a few things but could not get it worked out. He did say the valves were good. I am not sure I can disassemble myself so I am thinking just buy a new one.

 

The green sensor inside your air cleaner is part of what is called the Thermostatic Air Cleaner or (TAC) as Rescue explained.
If you remove the flexible cold air intake duct off the front of the air cleaner you will see the damper door.
It looks like all your hoses are there to the sensor and damper door vacuum actuator.
With the engine off the door should be open.
On a cold start the damper door should close, once the inside air cleaner temp rises between 85* & 128* the damper will slowly open. At temps above 128* the door should be full open.

Not that this is part of your lean condition, but I think your accelerator pump rod is in the wrong hole of the lever?

 

No, you cannot get a carb rebuilt for $150 - parts alone will run about that. Anyone who is building carbs for $150 doesn't have a clue what they're doing - skilled labor does not go for $17/hour. No, you cannot buy a new carb for $250. A cheap, piece of junk Edelbrock "Performer" runs about $350, and will get you a 15-20 horsepower loss over a correctly built stock Q-Jet. If you want the car to run right, you need to get out of the "cheap ditch" and pony up to do the job right...

Yes, it is. Which is indicative that somebody who does not know what they're doing has been into the carb. That means that the carb has several setup problems that are causing the isues. The carb needs to be torn down, inspected, and all the issues (there will be many) need to be corrected and set up right. Once done, that stock Q-Jet will perform really well - judging by the photos, the carb is in really good, original, rebuildable condition. Somebody has just messed with it to screw it up. Judging by the black exhaust reversion sooting in the carb's primary bores, they have also messed up the timing - typical signs of retarded timing with possible vacuum advance issues as well. The car has overall tuning and setup issues not limited to the carb.

Lars