it did affect me for a bit but I realize these are superfans and you have to know how to categorize input. Actually quite similar to some of my other interests.

I’m going to do some small steps to get my current setup running better while sourcing a Qjet for Lars to rebuild. He doesn’t know this yet but I’m emailing him now.

 

Most of the people here are great folks and are happy to offer good advice or constructive critisim.
Some are real a holes who sometimes scare away new members, and should be ignored.
If someone doesn't like a question, they can simply ignore it. It's not your problem.
So, the bottom line is, it's your car, and you can chose how you handle it.
Absorb all the different opinions and then do what is best for you and your car.

 

You will never get that running properly with the dreaded Square Bore to Spread Bore adapter....not only is the reversion caused by retarded timing, the mismatch on that adapter plate will never allow a clean pull through the venturi's.....and this is where you drive 99% of the time. Pull the carb off and you will see what I mean. Also, you have the vacuum advance on ported advance.....not the hot tip for a good idle.
You either have to change back to a Q-Jet or change the intake to the correct square bore pattern.
This "setup" you have we see here about twice a month and I see it in real life all the time.....just because it bolts on doesn't mean it's right. When you crack the throttle the engine vacuum wants to pull straight down to pull fuel out of those stanchions sticking out of the throttle bores....those are the boosters.....and no WAY will the vacuum make a nice clean suction on the boosters to introduce fuel.....it happens much too slow and then when you are driving you are in and out of the throttle.....the air hits the mismatch in the plate and actually goes the other way.......and the unburned soot from retarded timing comes up through the throttle bores and makes them black.
There is nothing wrong with that carb.....and there is nothing wrong with that intake, but there is everything wrong with that carb on that intake........
If this were here at my shop.....I would put a 2701 Performer EPS on it with 1204 Fel Pro intake gaskets and a good tune (timing, idle screws) and it will run great.....if you want to do it yourself, I recommend you find a nice rebuildable core and have Lars go through it......
On the current setup.....it is never going to run correctly. If you think it runs smooth now you will never be prepared what a proper intake system runs like on these.....
You have two options that are not too crazy......
On the Holley, Lars is correct on the black secondary spring.......you need to have yellow one in there.....also, someone need to set idle mixture, and make the floats are set correctly......

Jebby

 

Then you're doing better then a lot of Corvette owners.

A neighbor had the engine rebuilt for his 76. A friend's son, a 20 something "expert" mechanic pulled and reinstalled the engine. The expert told him Q-Jet's were junk and insisted he buy an Edelbrock carb. I explained to him the Edelbrock needed an adapter and it would cause hood issues. He told this to the guy doing the work, to which the expert replied that I was an a$$ and had no clue what I was talking about. He told him if he wanted to put the Q-Jet back on to get the car out of his shop, and find someone else to finish the work. So he bought the Edelbrock, found out it needed an adapter, installed it all and the air cleaner hit the hood. It never ran great and even with an aftermarket air cleaner the hood still didn't close right. Eventually he asked me to find him a Q-Jet and have it rebuilt. After a year, and wasting about $800 on the wrong carb, an adapter and an air cleaner, he now has the right Q-Jet, the hood closes correctly, and the car runs the best it's run in the 12 years he's owned it.

So you're already ahead of some Corvettes, even some long time owners.

 

Those are commercially rebuilt/remanufactured carbs that you don't want to touch with a 10-foot pole. Complete junk, and most of them actually won't run. Not what you're looking for. Avoid all "pretty" carbs.

Just sent you a response to your e-mail.

Lars

 

Been doing a lot of reading, both here and the 74 AIM. It only helps so much, as the Holley 4160 is obviously not reflected in the AIM.

Based on the advice here, I:

• Switched the distributor advance vacuum to a full manifold vacuum part on the Holley 4160 carb (one was capped off).
• Discovered the EGR vacuum tube was disconnected (this smelled like gasoline, I hope this is why I noticed the smell near the engine over the last week but couldn’t find any leaks).
• Hooked the EGR up to the ported vacuum on the carb (that the distributor advance was previously plugged into).

Now I need to:

• hook up vacuum gauge to manifold pressure vacuum on carb (I'll go with the one currently on the brake booster)
• Reset to mixture screws fully in, then 1.5 turns out from seated. Start car and reach warm temp, then adjust idle mixture screws (equally) until stable max vacuum is achieved (between 17-22?).
• Then, adjust curb idle speed screw to achieve desired idle.

I plan to follow the procedure as spelled out in this manual which is very similar to the 80457-10:
https://documents.holley.com/199r11081.pdf and as they describe here https://www.holley.com/blog/post/her...ure_and_speed/

 

1. comfortable changing out the fuel line, looks like a stock pump in stock location. I’ll double verify. Looks like zip corvettes has the part and angled adapter.
2. Well, that didn’t make an immediate improvement. I moved the distributor advance vacuum to the manifold vacuum on the carb. I did suck/blow on the tube first, and nothing happened. Just resistance as if it was a straw closed on the other end. [I now see another Lars post that makes me think I needed to remove the cap and rotor to see if sucking moved a lever] I discovered the EGR vacuum tube wasn’t connected to anything (other than the EGR), so I attached it to the ported vacuum on the carb where I just pulled off the distributor advance. After starting and warming, I adjusted the idle (which was a few hundred RPM higher than before moving hoses) down to 850 and followed Holley’s steps to adjust the idle mix and and best I could get was about 18” vacuum, but a lot more misfire and rough running (possibly knocking too) - more noticeable exhaust sputter. Carefully stepped 1/8 turn on each side going more lean or rich and just couldn’t get it to settle.
   
   Suspecting I desperately need to adjust timing or there’s another issue, I don’t have a timing light (yet) so I put things back as they were, except I connected the EGR back to the manifold vacuum on the carb instead of just venting into the engine bay. I am wondering if this is a timing/spark issue? It runs “good enough” back almost the way it was, but I may either try again with the vacuum advance on the manifold vacuum instead of ported, or take it to a mechanic I trust… or just not and get the Qjet sorted with Lars. It turns out I’m an idiot and keep looking for the wrong thing on eBay.

maybe it didn’t sink in before, or maybe reading this and other comments again after having learned more and trying a couple adjustments for real, but this makes me feel better about having trouble today. Changing the spring seems straightforward enough, but again not sure the effort is worth it if I’m removing the Holley in the coming weeks. I didn’t check the floats. Was less comfortable with having fuel possibly come out while the engine was running. I can look back into that if people think it will help.

but if the square/spread mismatch is always going to run a little rough it just sounds like efforts to tweak it are a waste. I was just hoping to make it a little better in the interim.

 

Also, it seemed the electric choke didn’t close the choke plate on cold start. So I’m going to check that over too, make sure it’s getting 12v and good ground. Tried tracing the wires but lose track after a bit without feeling it was necessary to undo some bundles in there.

update: multimeter confirmed 12v at the choke. Will have to look again tomorrow to see if choke works on cold start.

Feeling pretty defeated.

 

Don't get defeated, and don't worry about anything else until you get the timing set. Email @lars for his timing papers, and order a timing light.

I use a digital light with dial-back. Or you can use a standard light and timing tape, as shown in the video below. But you'll want a digital RPM readout for the next steps, at least.

 

Here's a link to Holley's manual of their current model of this carb. This might help you tune it.

https://documents.holley.com/199r11081.pdf

 

Any updates? If the car starts, you don't need the choke, it just helps get it started from cold, and helps warm up the engine faster.

On a Q-Jet (and likely on that carb too), it will take two quick pumps of the gas pedal to reset the choke, such that it starts closed with a cold engine (and a cold choke coil).

Absolutely worth fixing, and should be easy once the timing is sorted.

I find this Innova 5568 timing light really easy to use.

 

I learned the Holley choke needs the accelerator to be fully depressed to the floor once to activate (with ignition on) on a cold engine. So that solves that mystery for me.
I also zeroed in on that 5568 as my likely timing light purchase.

The overall update is I got new tires put on last week as that was safety priority #1. While waiting, I called and talked to the PO, and to a local mechanic I've entrusted my Volvos to over the years. He's not an expert in Corvettes, but he works on all years cars and mainly, he's honest and that can be hard to find.

Essentially the mechanic helped get my head on straight and helped me prioritize. I have a slight transmission leak from the front seal area, and that needs to be addressed before we go into tuning anything else. From there, he's willing to go through the car and cover some basics like checking compression, check dist/plugs/wires, timing/verify TDC, I believe carb was last on the list but we were just chatting. Point was not to get ahead of myself, and also spend more time learning the car, as I initially thought it was "running great" and I agree, I need more time to tell what's truly an issue vs. just different as a 50 yr. old V8 vs the ultra-modern 4 and 5 cylinder turbo/electrified hybrid engines I'm used to driving.

Talking to the PO was illuminating:

• the car does not have a stock cam, as he initially told me on purchase. I ran the specs by Lars and he suggested to toss it and get an L82 cam. If I were to talk cam further, I'd start a new thread.
• The carb was sooty back when he got it (and I guess he just never cleaned it??).
• PO thought the harmonic balancer may have shifted a bit over the life of the car. Last he adjusted timing he did it by ear . When he installed the cam he figures he would've verified TDC but doesn't remember. But he thought "using that line didn't seem to be where the engine made the most power" -- all I know is this just underscores timing should be checked. I don't look forward to figuring out TDC with my current amount of experience.

So this is where I'm at currently. I'll get the transmission done. In the meantime:

1. Went through process of Learning Carbs With Lars and found/purchased a good Qjet candidate for rebuild from eBay. I'm going to have Lars work on it, but I'll need to time it right so that I'm ready to swap carbs when it arrives. So I'll see how the transmission goes before shipping.
2. Clean the carb and see if/when soot re-appears.
3. Replace the distributor rotor - mine appears a bit worn. Will maybe do the cap too since it's not expensive, even though mine appears to be fine. I would do plugs & wires, but I don't have a lift and it sounds like a few of the plugs will be very difficult to access.
4. I haven't properly verified if the vacuum advance actuator diaphragm is properly operating. I can't see the lever inside the distributor because of the electronic module that replaced the points & condenser covers too much for me to see if the arm is moving when I suck on the tube (I also don't know what I'm supposed to tell by sucking on the tube - it's like sucking on a clogged straw).
5. I need to verify the EGR is properly operating. It's not an expensive part and mine is a little ugly with the surface corrosion, so I may just replace the part.
6. At some point after transmission, I'll attempt timing again, or have my mechanic assist. But I need to decide when I'm going to swap carbs. I may wimp out and have the mechanic do both so it's done right.

Then maybe at some point next year I'll have a shop do the cam. If I couple that with a Vintage Air AC install, that's probably enough work that the vintage shop I know will take on the work.