What should I have?

[bolisk]

Hello!

Carb newbi here.  Now, haveing said that I'm not completely numty headed.    I've spend the last three years restoring my 1970 corvette, and I've rebuilt every component on the car except for the engine and carb.    Ironically those were the only two elements on my car that were very strong and worked without issues.  Having said that, I think it's now time for me to rebuild my carb, and I'm look for some advice.  Next I will explain my cars set up.

My Vette left the factory with the L46 option.  350 cubic inch 350 horse power with 11:1 compression.  The origional owner blew the short block at some point in the early seventies, and the short block was replaced with a 1974 unit.  The heads, intake and carb are origional to the car.

The second owner (I am the 3rd), had the engine rebuilt in the mid 1980's when he spun a main bearing.  The previous owner had the short block rebuilt to 1970 LT-1 corvette specs.  It has all forged and balanced internals, with mechanical flat tappet solid lifters with pink rods.  It also has (according to him) the correct 1970 LT-1 Cam shaft (does anyone know what the specs are for that cam?  I'm pretty sure it was not a 30-30 cam).  He had the heads rebuilt and had the press roker studs replaced with threaded units.  The intalk and carb remained unchanged. (I know the origional LT-1 had a different intake and a holey carb). . .so mine isn't all LT-1, but it sure pulls like one.  I also know the LT-1 heads had push rod guides. . .which mine does not.  When the engine was rebuilt, it was bored 30 over and the previous ower swears up and down that the car retains it's 11:1 compression. . .even though it runs on pump 93 octane gas.  I can tell you the cranking compression is ~210 psi per cylinder.

Having said that, after looking at the plugs it past week. ..the car now seems to be running lean.  Having said that, the air temps have been in the 50's.  And i've never checked the plugs after driving the car in cool weather.  Last time I changed the plugs. . .in the summer, they looked fine.  But I'm not sure if i have a mixture problem. I was told that the quadrajet has a winter and summer setting for the accelerator pump, would this cure the problem?  SHould I move the push rod to the other hole?

Secondly, I was wondering what my quadrajet should have as far as jets and needles go, with an 1970 LT-1 CAM, 11:1 compression, and everything else mentioned above?  

ANY and ALL advice / opinions would be apprecated.

BTW: what started all this was that my car has developed a misfire arround 1600 rpm.  I'm haveing the car scoped this week. . .but I started looking into this early.  

Best Regards,
Jon

[Cliff Ruggles]

Complete waste of time to evaluate the carb by reading the plugs.  Go by performance instead. If it's lean on the primary side, the engine will let you know.....surging, hesitation, lack of power, etc.  If it runs fine, the mixture is fine.

What are the head casting numbers?

GM made a LOT of different cylinder heads back then.  Some are excellent, some OK, others are pathetic, in terms of performance potential. 

The original heads should have came with screw in studs and guideplates, and were outfitted with larger valves as well. 

What is the carburetor part number?  Impossible to supply any specifics without it....Cliff

[bolisk]

So, dont have the casting numbers off hand.  The dar left the factory with the L46 option, which was the 350 hp with 11:1 compression.

The dar has the origional heads intake and carb.

The heads have been modified for screw in rocker studs.

[bolisk]

I'll have these numbers at the end of the week.

In the mean time, can someone answer the following question:

If I take a 1972 Quadrajet, from an unknown source car), and plan to use it on a 1970 Corvette, when I rebuild the carb, using the Cliffs Performace HP rebuild kit. . .and I "adjust" the carb as shown in the docuementation that comes with the kit. . .should I use the "measurements" for the adjustments found on the 1970 Corvette 350 line of the table. . .or should be using a 1972 (whatever) car for the specs.

I'm having a debate with my friends.  Normally, I would just rebuild a carb, and leave all the adjustments the way they were. . .but this 1972 carb is not even close "adjustment wise" to what the specs on the chart for the 1970 Corvette say.  The debate is whether or not the "adjustments" are specific to the way the carb is built, or specific to the use of the carb on an engine for a specific application.  There is debate that if I chage the adjustments of this carb away from factory. . .then the carb will never work correctly as the adjustments are specific to the carb. . .and not the engine that it sits on.

Any help would be apprecated. . .

-Bolisk

[omaha]

    All adjustment specs in a book are just a starting piont. and if the engine or the carb is different than stock, you can throw those specs out the window also. Heck, even the dealership mechanics did not use the specs and sometimes even the factory would send out a bulletin stating that they have changed specs and the old ones are no longer good. Think about the idle mixture plugs that were removed by the dealership mechanics be cause of customer co,plaimts. What is the correct way to do it? You must optimize your settings by various methods! For example, optimizing your idle mixture could be done with a vacuum gauge and some knowledge. Optimizing the choke settings could be done with trial and error techniques. The APT setting could be set using an O2 gauge or trial /error also ( if you know what to look/listen for). setting up the secondary could be done at the dragstrip.
     As far as the specs for airbleeds/ idle bypass/ idle restrictions/ rods/ etc....those are in the recipe's in the book. You just match a recipe to your situation. things like float level specs are really not as important as yu would think when it comes to a 32nd of an inch in eiher direction. heck if you dint have a spec for a float level, you just set it to 1/4 inch and it usually is fine. so the carb nust natch the engine and the specs ( the ones that are tunable) should be optimized by adjusting them with equipment and/or knowledge.
this is called "carb tuning".