Please allow me to try to explain my problem:
'79 w/ built 400 hp engine from 350 block w/ Holley #0-80457SA carb.

Everything was fine after getting modified engine (still have original stored away)....then I got in it & hit the brake pedal & it SLOWLY stopped but I could tell there was no "power assist". I removed the line going to the booster & there was only 3" mercury vacuum...I disconnected everything else from that line where it was "T" & got a good 12" mercury...which told me there was a leak in the vacuum system.....

I rebuilt the headlight actuators & put in new actuator relays (as 1 actuator & both relays were leaking) & replaced all the headlight vacuum lines:

Got all the crap hooked up including all new vacuum lines.
I THINK I've got power brakes, but only drove it from the garage into the "barn work area"......

After gettin' all done, I fired it up.....and it's STILL runnin' rougher than a corn cob....hardly idles, and smells rich.

(1) Got the vac. line from the intake manifold DIRECTLY to the brake power booster....nothing else at all on that line.
Before, the intake manifold line went DIRECTLY to the PCV valve....nothing else.

(2) Got the vac. line from the back of the carb DIRECTLY to the PCV valve....nothing else at all on that line.
Before, the line from the back of the carb went to the brake booster, and had a "T" that went to
the small vacuum canister beside the driver side fender....plus another "T" that also went to the canister.

(3) Got the vac. line from the front of the carb (a lot smaller fitting than the 2 above lines) going into the new vacuum filter,
on to the vacuum check valve [and it checks GOOD], and from the SMALL fitting on the check valve going thru the firewall,
[on to the light switch and "pull down" switch for the headlights] then going to the top fittings on the headlight actuator relays.
The BIG fitting on the check valve is going to the headlight vacuum tank between the headlight actuators, and also has a "T"
in it that has the REALLY SMALL vac. line going to the heater/defroster switch.
Before, the line from the front of the carb went EXACTLY the same as described in (3).

I have NOT checked the connections at the light switch OR the "pull down" switch, OR to the heater/defroster switch.

The line that previously was a "T" from the booster to the small canister is no longer a "T", it's just left open line to the canister.
The only lines at the small canister are one going to the windshield washer & gas tank. It's impossible to tell exactly where the
lines go to at the small canister, as the windshield washer is in the way.....
I really feel my problem is an incorrect connection in the lines from the carb.....I'm thinking about changing the line from the rear
of the carb that now goes to the PCV valve, and connecting it to the vac. system for the headlights, and making the line from the
front of the carb to the PCV valve.

I know all this probably sounds confusing....I've tried to make it as understanding as I can.....I hate to think I have to take it to
a Vette place....SO....I'm "reaching out" for any and all input I can get to get this beast back on the road!

IF I have to, I'll go back & make everything the way it WAS...and I'll probably end up w/ no power brakes, but the engine will
probably run good...but I'm still not driving it til I get the power brakes working!! So I'm not sure what that will gain me.....????
[Except for the fact that in that scenario it SHOULD let me know if I no longer have a vacuum leak.....???]

I appreciate any feedback!

 

Cap off all vacuum ports, and see how it runs.

 

Isolate all vacuum lines, install vacuum gauge.
add components 1 at a time until vacuum drops.

 

UPDATE:
I got 'er runnin' purdy strong !! Getting 17-19" at the front carb fitting AND the intake manifold.
Got the headlights working GR8, and I found that after fixing the leaks in the headlight vac. system, the vac. line at the REAR of the carb. would cause the engine to die as soon as I tried to hook it up to the PCV valve, or even try to hook up the vac. gauge to it...but w/ it left OPEN, the car runs good except for stumbling just before I hit the accelerator to GET WITH IT! SO....I'm sure now that something is not tweeked just right at the carb.
Took it on the road...runnin' stronger than ever when I get past the initial pushing on the accelerator, but until I get to a certain rpm, it stumbles...this is with the rear vac. fitting OPEN...and I'm sure my problem is in the vac. at the carb. now....and I'm NO expert on Holley's.....I DID adjust the float level & idle mixture screws [w/ a vac. gauge], but it didn't help much. I did the float level & idle mixture adjusting based on a knowledgeable friend that said it sounded to him like the engine was running too rich & needed more air.
SOOOOO....if this makes any sense, this is where I'm at: TRYING TO FIGURE OUT WHAT I NEED TO DO TO ELIMINATE THE LOWER RPM STUMBLING & ENABLE THE REAR CARB FITTING TO BE HOOKED UP THE THE PCV VALVE....I CAN FEEL A SUCTION AT THIS LINE, BUT THE ENGINE DIES AS SOON AS I PLUG IT.

I tried calling Holley twice, but was on hold forever.

ANY AND ALL ADD'L. HELP IS GREATLY APPRECIATED!!
THANKS TO ALL!!

 

increase idle speed, cap rear port, increase until it runs

 

Sunracer....appreciate the feedback....
Question: friend of mine who knows said he thinks it's running RICH.....for my own curiosity, will your idea help with the RICH condition....or don't you think it's running rich?

Thanks again!

 

If it's an off idle stumble/hesitation, then try increasing your squirter size by 2 numbers at a time until its gone.

 

Sounds very similar to the problems I'm having, mines a 70 so no fuel vapour system and no power brakes so if anything should be easier to get right but it's always seemed to be running rich.
Very hard to get a good idle and stumbles at light throttle which makes smooth, slow progress almost impossible, reading my Holley book it suggested cracking the secondaries open a little with the stop screw which means you can get the primaries closed further and get the idle screws working again, this did help a bit but it's still not right and VERY thirsty, I'm guessing around 5MPG and they're English gallons not your little American ones!
I'd obviously be very interested if you have any success and will share any discoveries I come up with!
Regards
Graham

 

Your squirter size needs to be increased. The accelerator pump cam needs adjusting probably as well.

 

I already get a puff of smoke when I hit the gas, is that not an indication of too much fuel, would an increase of squirter not just make that worse?
Graham

 

Sluefoot - It could be rich, but I think leaving the vacuum port behind the carb open is causing your idle speed to increase. There shouldn't be any uncapped or unused vacuum ports (i.e., nothing left open to suck in air)

First I would cap all ports - then adjust carb idle and mixture screws until you get a good clean idle first.

After that, I would check timing initial and mechanical advance to make sure it's a good match for your cam/head combo. I assume from your description these are aftermarket and probably more aggressive than stock (which suggests you may need a more aggressive timing setup).

After you have a decent idle, start tuning - rule of thumb is get timing dialed in first, then tune the carb as needed.

 

I dont have a holly but I do have a 79 L48 that has been replaced.

I have a edelbrock preformer series carb. I have mine hooked up as follows.

1. I have the PCV port (center front) hooked up to the valve cover.

2. I have the rear port hooked directly to the brake booster

3. I have a T on the manifold for Auto Transmission/Lights/etc

4. I have the vacuum canister on distributor hooked up the the port on the front of the carb.

5. The last port i have capped (driver side port)


Here is a link to pictures of the carb that will give you an idea of what I am talking about.

https://www.summitracing.com/parts/e...FZ2PswodO3sODQ

 

Showin' my ignorance here....what do you mean by "squirter"?
Are you referring to the jet, or accelerator pump, or....??

 

Squirters are your accelerator pump nozzles. There is one for each primary barrel. They need to squirt fuel immediately when the gas pedal is pressed. Check your throttle cable for any slack and remove it. Make sure your squirters are squirting at the instant the throttle cable is moved i.e. at the slightest movement fuel will come out from the squirters.

 

(1) Got the vac. line from the intake manifold DIRECTLY to the brake power booster....nothing else at all on that line.
Before, the intake manifold line went DIRECTLY to the PCV valve....nothing else.

(2) Got the vac. line from the back of the carb DIRECTLY to the PCV valve....nothing else at all on that line.
Before, the line from the back of the carb went to the brake booster, and had a "T" that went to
the small vacuum canister beside the driver side fender....plus another "T" that also went to the canister.


Swap these two hoses around. Leave no open ports on the carb.

 

Yes if the floats are adjusted correctly. It would produce black smoke with too much pump shot and probably stall the engine.

https://static.summitracing.com/glob...y-0-80457s.pdf

 

Thanks for that info and the link which was very informative, not quite the same carb but my choke is powered from the coil which they say is wrong so will try a different power source for that.
I'm going to disconnect all the vacuum system apart from the distributor and PCV then go through timing, valve settings and hopefully get somewhere with my vacuum gauge.
After my carb rebuild I set the float levels, the front float was plain sailing but when I came to do the rear one it was sucking in air when I took out the level plug, is this normal? I had to put my finger over the hole while I made the adjustment to prevent the engine from cutting out and with the air rushing in it was hard to gauge the actual level.
Thanks
Graham

 

Yes it is very important to have 12v at the electric choke. Your choke may not open all of the way. This could cause a rich problem.

The floats should be adjusted to have a little trickle of fuel comimg out of the site plug hole. Sounds like you are making progress.

Did you swap the brake and pcv hoses?

 

Just spent this afternoon running a new supply to the auto choke, just to be on the safe side I ran 12v from the horn relay through a relay so the power to the choke elenment isn't straining a 47 year old ignition switch, I found an ignition switched wire which Bubba had cut off at the firewall so used that to control the relay then fitted a 10A fuse to the supply to the choke, I'll probably need to richen the choke a bit as it comes off quite quickly now.
My hoses are simpler as I don't have power brakes, it was sluefoot with the hose issues.
Graham

 

After I ran in the new supply for the choke I moved on to valve setting and timing, valves were pretty much OK but when it came to the timing I have a really wierd situation, using my vacuum gauge I found what seemed to be the sweet spot giving just over 10inches of vacuum, trouble was when I put the timing light on the marks were nowhere near, in fact I had to dial in around 40 degrees on the dial until they came in sight.
Next I stopped the engine and turned it over until the mark on the damper was in line with the 0 mark, I then popped the dissy cap and found the rotor was pointing to lead number 8, next I took the plug out of number 8 and had a look with my endoscope expecting to find the piston at TDC but it was below TDC, I gave up at this point as it was getting late and my brain was aching!
Even if I was one rev out the opposite cylinder to 8 is 5 so that can't be the answer, I'm going to take number 1 plug out this morning to see where that one is, according to the timing marks it should be TDC on either compression or exhaust stroke, I'll let you know what I find.
Changing the choke supply has made a difference to the idle and I had to adjust the idle mixture screws to get a good idle so I can only guess the current drwn by the choke was afecting the spark.
I'll post more as I progress.
Graham