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Username Post: 1970 camaro carb from helll        (Topic#357773)
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-23-19 05:58 PM - Post#2773912    

Long time no see. Came back to visit the best place on Chevy info. Bear with my lack of responses. Can't get computer at home right now, so I'll check in to see, maybe tomorrow to see what yall come up with.
A friend has a very sweet 1970 Z28 with an LT 1. He re did the carb and it's not doing so well. He cleaned it and installed a new power valve. Had almost no vacuum yesterday when I went over to offer assistance. Discovered this afternoon after pulling the front bowl off, that he had a wrong gasket........ gas had even been making it into the vacuum line to the distributor.
The correct gasket is in now.
Car sounds much better, but still smokes and it's sucking a lot of fuel just idling as we mess with it........... so we have too much fuel consumption, but don't know why.
We can't find any major or obvious vacuum leaks.
It has the original Holley 780 vacuum secondary carb.
Here's where we are:
Fuel levels are at or slightly below threads of the screws, so that wouldn't cause smoking or high fuel consumption.
Idle screws are 1 1/2 turns open.
New 5.5 power valve was installed today.
Initial timing is about 8 or 10.
Vacuum never got above 3.5 ...that bothers me. When timing was 15ish, we didn't get much more, maybe 5 with vacuum can hooked up.
His only real engine mods are some World Products Sportsman heads, stamped 11.25. Engine was rebuilt to factory specs with a stock blueprinted cam and those heads.

So we have high fuel consumption, smokier and stinkier than normal exhaust, very low vacuum and changing the timing does not raise the vacuum much....... 5 is about it. I read it ought to be closer to 13/14ish. Float levels seem about right... not above the sight plugs.
It ran fine before the carb was cleaned, but he did add a power valve blowout valve in both the front and back of the carb. Not sur if the back screwed this up.
Ant advise appreciated. I'll check in tomorrow if I can. Thanks in advance!

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 


Shepherd 
Frequent Contributor
Posts: 1813

Loc: Lake George, NY
Reg: 11-11-15
08-23-19 06:24 PM - Post#2773915    
    In response to ranman

With that low vacuum, nothing is going good with this, the power valve is open of course, way too rich. Make sure the secondaries aren't partially open for some reason.



 
Bad56Sedan 
"13th Year" Gold Supporting Member
Posts: 1118
Bad56Sedan
Loc: Pasadena, Texas
Reg: 04-29-04
08-23-19 08:18 PM - Post#2773923    
    In response to ranman

What happened to me,
I too had rebuilt my Holley carb, 750 DP
Same effects as you describe,
Fouled plugs several times,
I too changed the power valve to a 5,
Double checked the spark plugs wires,
But it had to be the carb, only thing I changed,
Low vacuum also,
The Holley kit I bought had several gaskets for the top of the base plate.
It was the correct kit for the carb, but the upper base plate gaskets were minutely different.
The gasket between the base plate and the barrels, don't know the name.
Then I saw it, I had chosen the wrong gasket.
The difference was so slight I did not notice, it was either a hole was covered or there was a hole , small difference don't recall which way it was incorrect.
That was the issue, heck I was even looking to mail the carb to Acme Rip Me off carb shop and see if they could fix it.
Luckily I found it, might be your issue,maybe .
Let us know what you find out.

VC56S 2 door Sedan, 39 Years



 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-24-19 12:09 PM - Post#2773955    
    In response to Shepherd

Before discovering he had a wrong gasket in the metering block, I opened up the secondary screw a turn and a half because I noticed the idle trasnsfer slot was showing like 1/4". I figured opening the secondaries a little would allow the primary to be closed. That didn't work. Still too much gas/smoke, and idle screws could still be turned shut. Vaccuum was about zero.
After discovering the gasket was wrong and correcting that, I closed the secondaries then turned the screw one turn open as per a Holley carb book. So I think we are good in that respect. Idle screws still have little effect if any even tho we were able to close the primaries considerably.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-24-19 12:26 PM - Post#2773959    
    In response to Bad56Sedan

  • Bad56Sedan Said:
What happened to me,
I too had rebuilt my Holley carb, 750 DP
Same effects as you describe,
Fouled plugs several times,
I too changed the power valve to a 5,
Double checked the spark plugs wires,
But it had to be the carb, only thing I changed,
Low vacuum also,
The Holley kit I bought had several gaskets for the top of the base plate.
It was the correct kit for the carb, but the upper base plate gaskets were minutely different.
The gasket between the base plate and the barrels, don't know the name.
Then I saw it, I had chosen the wrong gasket.
The difference was so slight I did not notice, it was either a hole was covered or there was a hole , small difference don't recall which way it was incorrect.
That was the issue, heck I was even looking to mail the carb to Acme Rip Me off carb shop and see if they could fix it.
Luckily I found it, might be your issue,maybe .
Let us know what you find out.


That sounds like the next plan for us. I'll check to see if he saved the old gasket. He bought a kit with a bunch of bowl gaskets, needles and seats and power valves.



~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
93 low 
Poster
Posts: 68

Loc: So Cal
Reg: 12-06-11
08-24-19 04:55 PM - Post#2773969    
    In response to ranman

I don't know if this might help. I have a Holley 780, dual feed, single pump carb on my boat. 455olds, 390hp with 76 main jets with 80 metering block and it's spot on. If you don't have 390hp, you might want to go down in size on the mains & metering block.
What size mains & metering block are you running?



 
93 low 
Poster
Posts: 68

Loc: So Cal
Reg: 12-06-11
08-24-19 05:06 PM - Post#2773970    
    In response to 93 low

I have a Holley 4360 economaster or economiser, 4bbl carb on my 76 K20 truck, small block 350. The simplest carb I've ever ran.




 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-24-19 05:31 PM - Post#2773972    
    In response to 93 low

  • 93 low Said:
I have a Holley 4360 economaster or economiser, 4bbl carb on my 76 K20 truck, small block 350. The simplest carb I've ever ran.



This is an LT 1. It's made for fun and he's keeping the car stock. The 780 Holley carb was factory equipment on this 1970 Z-28. Most GMs used Rochesters, but this car is a special one. Car looks like new even tho it's 50 years old. Even the paint and upholstery look almost new. He was hoping to take it to a car show this weekend but we couldn't get it running well enough.
Personally, I don't think the carb is overly intimidating, but I've never worked on this model.
Holleys aren't known for being overly complex because they don't have very many parts.
My friend took it apart and rebuilt it, so I'm late in the game and trying to figure out why it isn't working like it was before.
I have a Holley book, I'll check out that carb you mentioned to see what it is.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-24-19 06:02 PM - Post#2773975    
    In response to ranman

Thanks for the input guys. I'll let him know what you said and we'll proceed from there.

How critical is float level on these carbs? Both front and rear are set at or ever so slightly below the sight plugs....... kinda hard to tell because of the cam jiggling the engine a bit. My engines (unfortunately)don't have that problem.

I adjusted the secondary screw one full turn open after the throttle plates were fully closed. I assume that will be OK for this engine.

How much initial and total advance do you think this engine needs? I think he had it set on 8 or so before he took things apart. He's using supreme gas, so maybe 8 is all he can do with 11 or 11.25 to one compression. This is a new area for me.
Cam is a blueprinted one with factory LT 1 specs. .458/317 intake and .484/346 exh
If you have any other suggestions keep em coming and I'll check back in Monday. Thanks again.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
aghaga 
"4th Year" Silver Supporting Member
Posts: 2212
aghaga
Age: 64
Loc: Altavista, Va.
Reg: 07-05-08
08-25-19 06:30 AM - Post#2773992    
    In response to ranman

That is a solid lift cam. What is the valve lash set at? Too tight and you would loose vacuum.



 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-26-19 03:00 PM - Post#2774092    
    In response to aghaga

I have no clue about the valve lash, but it was running fine before the carb rebuild so I don't think that's an issue. It might be a week before I can get over to see the guy, so for now, we need to check the carb gaset. If that doesn't fix it......... aaahl be bach.
I'll be back either way.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
66cayne 
Silver Supporting Member
Posts: 2843
66cayne
Reg: 08-06-08
08-27-19 08:55 AM - Post#2774178    
    In response to ranman

Your float level sounds fine, just at the bottom of the sight screws. 1/4" on the primary idle transfer slot is WAY too much. The idle mixture screws are not going the function. If you were getting fuel in the vacuum line are you sure its not puddled in the vacuum canister as well? I think you need to break the whole carb apart and start from scatch with a new rebuild kit. Its a shame he has to settle for 8 degrees of initial advance. What is the vacuum advance rate and total set at? He might be able to run more initial if he can limit the vacuum advance rate.



 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-27-19 03:54 PM - Post#2774207    
    In response to 66cayne

  • 66cayne Said:
Your float level sounds fine, just at the bottom of the sight screws. 1/4" on the primary idle transfer slot is WAY too much. The idle mixture screws are not going the function. If you were getting fuel in the vacuum line are you sure its not puddled in the vacuum canister as well? I think you need to break the whole carb apart and start from scatch with a new rebuild kit. Its a shame he has to settle for 8 degrees of initial advance. What is the vacuum advance rate and total set at? He might be able to run more initial if he can limit the vacuum advance rate.


It probably has a vacuum can with 20 degrees, but I'm, not really sure. I did the 8 degree mod on my '73 years back after learning that from I-man. Since he's only going to have 13 or 14 when we get it fixed, I'm not sure if it's going to make a lot of difference. Funny you mentioned that, as it was on my mind.
He probably had some getting into the can if it was in the hose.
Early on when I saw the 1/4" of transfer slot, I figured the best fix was opening the secondaries a turn and a half further, so I did.
............only after that did we discover the wrong metering plate gasket......... so I reset the secondaries to where they were, and put in the correct gasket. Like was mentioned, It will come apart again to see it any other gaskets are wrong or damaged.
I'm gonna ask him about the cam adjustment......... I recall that he had not changed the settings. As I age, "recalling" isn't as easy as it used to be.
This is sort of a refresher course for me. My last Holley rebuild was a 650 spread bore emissions carb with the blunt revers idle screws.
Bought it by mistake thinking it was a simple vacuum secondary carb. Took me quite a while to get that one modified into a workable unit.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-28-19 07:55 PM - Post#2774354    
    In response to ranman

OK, we found the gaskets were correct..... not what we were expecting, ...but good.
......however, we found a "screwy" problem. The base plate has 8 drilled and tapped screw locations, but he only had six screws installed.
I removed two screws in the center, and they looked like it was the first time then had been installed in those locations. Perpendicular to those two center screw locations, are two more screw locations (they make a triangular shape within the 4 corner screws in the plate.)............ those two had no screws in them, but it looked like screws had been removed and installed numerous times in the past.
......so it looks like two of those locations are left empty. He had the screws in the wrong two holes. I saw in a Holley book, there were two empty screw locations. Why not have screws in all the holes to more evenly clamp the load?
Should we bother adding two more screws? Why did Holley not put them in?
One other think I noticed is a hole dead center in the plate. It's about 1/4 to 3/8 inch in diameter. I could poke a narrow screwdriver almost 2 inches up into that hole. Is it a problem? He has not been using a 4 hole base gasket, but I think he should...... the manifold has 4 holes.
I'm gonna look in my Holley book when I get home to see if it shows those base plate screws being unfilled....... just seemed odd.
Any input would he helpful, but we may have this solved. Probably won't be working on it till this weekend anyhow.

Here it is. This explains gas in the vacuum line, let alone everything else.
https://www.youtube.com/watch?v=b8ROjrGAH2I

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


Edited by ranman on 08-28-19 07:58 PM. Reason for edit: No reason given.

 
Bruces 57 
Frequent Contributor
Posts: 2415

Reg: 01-03-07
08-29-19 07:13 AM - Post#2774386    
    In response to ranman

Hello;
NOT WHAT YOU WANT TO HEAR RIGHT NOW!!, I know you want "bone stock" but "that was then, this is now" thinking needs to be used here!
Considering the amount of Ethanol in gas these days unless you have stations near you that have non-ethanol (boat gas) I got a Street Deamon Carb (composite fuel bowl) and my engine never ran as good as it is right now considering I have daily driven my car (57 chevy for years!!

Bruce



 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
08-29-19 06:49 PM - Post#2774448    
    In response to Bruces 57

It runs premium non alcohol...... we have that here so I feel lucky. Mowers start a lot easier with it.
I'm more concerned about the number of screws. Looks like if using a 4 hole manifold there's no way for a screw to get loose as many people say. Just seems like more even clamping pressure for the gasket. Should a low grip thread locker be used or is that overkill? The factory screws have lock washers.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


Edited by ranman on 08-29-19 06:52 PM. Reason for edit: No reason given.

 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10798
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-01-19 08:29 PM - Post#2774650    
    In response to ranman

Just a progress report. We removed the carb and corrected the base plate screw situation by installing the screws in the proper holes. We didn't censored the 7th and 8th screws since the carb never had them. I guess they just aren't needed.
Next, I closed the primary plates, then opened the the accelerator stop screw just one full turn. The idle transfer slot is barely showing........ smaller than a square hole.
The car cranked and filled the bowls, but never even tried to start. No huffs, puffs, nothing. I discovered the acellerator discharge nozzles and the so called "pill" was seized, not allowing a drop of fuel through. The engine started after we cleaned that screw and discharge nozzle. Then engine started right up and idled with the idle screw in that barely opened position once it warmed up for few minutes, so most of the problem is corrected. Time for some fine tuning of the idle air screws and playing with the timing.
Can anyone find what the factory vacuum level ought to be? Not with a modified advance system......... what it might have been fresh from the factory. We are only getting 6 or 7 even tho the engine runs fine.... Nice throttle response and no backfiring.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 


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