New replacement carburetor for 63 300 HP

[Frank D.]

Re: New replacement carburetor for 63 300 HP

Strange thread - it then must be presupposed that no part can be restored to operate like new, not master cylinders, not engines, not anything.
I'll put my Daytona Parts rebuilt carbs up against a new one (however I DID supply the core) any day - its probably better because of their redesigned float valve. I can name another 2-3 restorers that work to such a quality threshold. Bob Kunz, Chuck Smith.

Yes, if you go to some, no-name, high volume rebuilding outfit you may well get a crapola job - just like anything else... I guess its all in how you define "commercial rebuilder".

And percolation isn't a tame expansion of fuel to a pre-designated volume....its perc just like an old coffee pot...with bubbles violently pushing air through the hot liquid... It WAS a problem decades ago and carbs (like the WCFB) even featured special mechanisms to deal with it (as pictured).
These features helped but were not "cure-alls"; perc still occurred.

[Joe R.]

Re: New replacement carburetor for 63 300 HP

Steve,

Thanks for the "Seminar" on AFB carbs! Thought I knew it all but learned a lot from your observations and experience! Have had several 63 300HP and 340HP Corvettes. Managed to incorporate some of your suggestions and they ran like a new sewing machine! The castings are very rarely defective with the exception of the throttle shafts and that can be bushed. The rest is just adjustments and the correct installation using spacers and gaskets designed especially for the AFB. Cheers!

JR

[Stuart F.]

Re: New replacement carburetor for 63 300 HP

Bet a large percentage of 63 340 hp AFB's are running around with incorrect base gaskets. I never saw a top plate with accelerator pump guides so worn, but I have received a rebuilt carb with the leather folded over and no springs. Also, some rebuilders mix and match Venturi clusters.

Stu Fox

[Steve G.]

Re: New replacement carburetor for 63 300 HP

And percolation isn't a tame expansion of fuel to a pre-designated volume....its perc just like an old coffee pot...with bubbles violently pushing air through the hot liquid... It WAS a problem decades ago and carbs (like the WCFB) even featured special mechanisms to deal with it (as pictured).
These features helped but were not "cure-alls"; perc still occurred.

Yes, perc may still occur, but who cares? It's not the percolation that's the problem, it's the hard hot start and rough idle that is. And the hot idle compensators took care of that. The fuel can boil all it wants, as long as it doesn't affect the running or starting, what does it matter? And that's exactly what the hot idle compensaters do. If you still have those symptoms then you should focus on repairing the compensaters, not trying to drive the fuel temp down.

There's lots of cars out there with boiling fuel that run just fine.
Steve

[Timothy B.]

Re: New replacement carburetor for 63 300 HP

Strange thread - it then must be presupposed that no part can be restored to operate like new, not master cylinders, not engines, not anything.
I'll put my Daytona Parts rebuilt carbs up against a new one (however I DID supply the core) any day - its probably better because of their redesigned float valve. I can name another 2-3 restorers that work to such a quality threshold. Bob Kunz, Chuck Smith.

Yes, if you go to some, no-name, high volume rebuilding outfit you may well get a crapola job - just like anything else... I guess its all in how you define "commercial rebuilder".

And percolation isn't a tame expansion of fuel to a pre-designated volume....its perc just like an old coffee pot...with bubbles violently pushing air through the hot liquid... It WAS a problem decades ago and carbs (like the WCFB) even featured special mechanisms to deal with it (as pictured).
These features helped but were not "cure-alls"; perc still occurred.

In your picture those anti perculation vents are better known as air bleeds, so everyone make sure they are clear.

IMO, the best way to start an overhaul of a carburetor is to be sure of what's inside, after all this time it's hard to say who has altered bleeds and jets.

[Chester C.]

Re: New replacement carburetor for 63 300 HP

I know I stated that I did not want an Edelbrock, and that was because I thought it would not work on a 63 but will it. What exactly are the problems with using a 1406 Edelbrock. I know the fuel line and vacuum lines would have to be routed different but will it fit on a 63 manifold. Will the snorkel air cleaner fit and if so can you put an adapter to make it fit.

[Frank D.]

Re: New replacement carburetor for 63 300 HP

Yes, perc may still occur, but who cares? It's not the percolation that's the problem, it's the hard hot start and rough idle that is. And the hot idle compensators took care of that. The fuel can boil all it wants, as long as it doesn't affect the running or starting, what does it matter? And that's exactly what the hot idle compensaters do. If you still have those symptoms then you should focus on repairing the compensaters, not trying to drive the fuel temp down.

There's lots of cars out there with boiling fuel that run just fine.
Steve

I don't disagree IIRC the WCFBs don't have hot idle compensators; can't say on AFBs
I once installed the hot idle compensator in a Q-jet in my '75 pontiac backwards. Car would start, warm up and stall.
Took me a while to find it - felt pretty silly afterwards...

My objection to the Eddy carbs is that blingy look and the bright red logo on them...they are, for the most part, AFB clones anyway.

[Stuart F.]

Re: New replacement carburetor for 63 300 HP

Tim;

earlier schematics on AFB's called out these air bleeds as anti-percolation passages. Different models have different height brass tubes (stand pipes) over these passages (air bleeds).

Chester;

If you read all of the posts in your thread you will find most of your answers. Going with the Edelbrock 1460 would not be my choice as it presents too many adaption problems. It will never emulate a stock appearance unless you are up to changing to an AFB top plate with all the adaption that that in itself presents.

Stu Fox

[Steve G.]

Re: New replacement carburetor for 63 300 HP

Stu,

I think there's a reason the nomenclature was changed from the earlier publications. Carbs are carbs. They all have air bleeds in the idle circuit like that. I've never seen another manufacturer/publication refer to the air bleeds as an anti-percolation device.

WCFB's use a mechanical bowl vent which they refer to as the bowl vapor vent. AFB's use the bimetallic spring arm and call it the idle compensator valve. Orifices in the throat are air bleeds. I think the later publications were simply correcting an error.


Steve

[Stuart F.]

Re: New replacement carburetor for 63 300 HP

Steve;

Have you ever noticed the vapor vents on the 3460s and 3461s of 63 Corvette models? These may have been on the models for the 62 also, i don't know, but they surprised me. I read about them first someplace before I ever noticed them, and then it was one of them "oh ya!" moments. I have since plugged them with some rivet heads that fit snug in my efforts to reduce sources of excess gas vapor in my garage. Doesn't seem to make any difference both in the amount of vapor in the garage or the performance of the carburetor on hot restarts (as advertised).

The Bimetallic spring arm is the "Hot Idle Compensator". I recently did a hot water test on one of mine to see if it really did open and at what temperature (using a meat thermometer). I made a block off plate with gasket to eliminate this piece just for test purposes. Did not notice much difference, basically because the L-76 is a beast all year round no matter what you do to it.

Stu Fox

[Duke W.]

Re: New replacement carburetor for 63 300 HP

At what temperature did it begin to open up?

Duke

[Joe R.]

Re: New replacement carburetor for 63 300 HP

Steve;

Have you ever noticed the vapor vents on the 3460s and 3461s of 63 Corvette models? These may have been on the models for the 62 also, i don't know, but they surprised me. I read about them first someplace before I ever noticed them, and then it was one of them "oh ya!" moments. I have since plugged them with some rivet heads that fit snug in my efforts to reduce sources of excess gas vapor in my garage. Doesn't seem to make any difference both in the amount of vapor in the garage or the performance of the carburetor on hot restarts (as advertised).

The Bimetallic spring arm is the "Hot Idle Compensator". I recently did a hot water test on one of mine to see if it really did open and at what temperature (using a meat thermometer). I made a block off plate with gasket to eliminate this piece just for test purposes. Did not notice much difference, basically because the L-76 is a beast all year round no matter what you do to it.

Stu Fox

Stu,

Sounds like a man who lives the life of Riley in FLORIDA and expects his 340 to purrrrr like a kitten!!!!
I love the 097 cam!!!!!!!! It's the best all around camshaft ever made!!!!!
Hear that DUKE!

JR

PS. If you don't believe that ask Zora when you get there!

[Steve G.]

Re: New replacement carburetor for 63 300 HP

[QUOTE= Did not notice much difference, basically because the L-76 is a beast all year round no matter what you do to it.

Stu Fox[/QUOTE]


Stu,

That's the part that I don't get and what leads me to believe something was missed/is wrong.

The first Corvette I owned was a bone stock, all original, never apart 63 340. I bought it in 1974 and I was 19 years old. The $4300 I paid for it broke me and it was the only car I had so I drove it all the winter of 74-75. This was on the Canadian prairies (Winnipeg), -20 to -40 in the winters are the norm. For part of that winter my drivers license was a casualty of the 66 Nova I had built b4 I bought the Corvette, so the girl that would eventually be my first wife drove it part of that winter. It was a very well mannered car that even she had no trouble with in the dead of winter. Pump the pedal 2 or 3 times and twist her tail. Fired right up. Jab the pedal once to knock it off the top step of the fast idle cam and you could drive away. No stalling, no hesitation, no loading up right through warm-up to operating temp.

Prairie summers can be hot, albeit not Arizona hot, but 80-90's with the occasional foray close to 100. Ran just as well in the heat as it did in the dead of winter.

My only complaint with driveability was that the 340 makes little torque at low rpm and this car had 3.08 gears in it. Practically had to push it to get it rolling.

The engineers didn't screw up on this. These cars were designed and in the day able to operate without flaw from -40 to 110. If the car is stock you should still be able to do that without redesigning the system.

This has really hijacked the op's thread. I'm going to start another.

Steve

[Stuart F.]

Re: New replacement carburetor for 63 300 HP

Joe;

Doubt if Zora will remember me; the GM Tech Writer from the Locomotive Division (EMD) who owns a 63 Corvette. Not too much in common. He didn't like my idea of putting a 645 diesel engine in a Corvette. Ha!

Duke;

As I believe I reported back to you when i did the test (we posted back and forth on someone else's thread); the piece I tested had a #66 (or #99) on the bottom side and a circled "C" and "R" on the top. My first and only test showed some movement at 180 degrees with some additional opening (slight) up to 200 degrees. I stopped there and determined the test to be inconclusive what with the kitchen paraphernalia I had to test with.

FUEL DRIPPING BY THE THROTTLE SHAFT(OR PLATES):

1) After the engine is switched off, heat from the engine heats the fuel in the fuel line.

2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor.

3) The check valve in the fuel pump prevents the fuel from backing up through the fuel pump.

4) The pressure increases to a point that the float/fuel valve combination in the carburetor cannot withstand the pressure.

5) An amount of fuel (usually from a teaspoon to a couple of tablespoons) flows into the fuel bowl of the carburetor.

6) This raises the fuel level in the bowl above the main discharge nozzles.

7) Fuel flows through the main discharge nozzles and drips onto the throttle plates which are closed (or at idle open setting), and exits out beside the throttle shafts (and/or throttle plates) dripping onto (and/or into) the intake manifold.

SOLUTIONS

1) Avoid Ethanol laced fuel.

2) Buy lowest octane name-brand fuel that doesn't ping or detonate in your engine (higher grades tend to have more Ethanol).

3) Learn to live with it or institute lots of changes and hope they will pay off. No one cure all.

Air bleed on primary venturi clusters with brass tube is still called; "Air Bleed and Anti-percolator vent"

Stu Fox

[Stuart F.]

Re: New replacement carburetor for 63 300 HP

Forgot to mention about my water test of a Hot Idle Compensator that the bubbles in the hot water makes it darn hard to see if the valve is lifting off the seat. If I were to do it again I'd probably have to change to a different medium like oil or something that would allow visible detection of movement above the 200 degree level.

Joe;

I too love the 097 cam. My favorite example was my 56 Chevy with a 58 Fuelie engine with dual glaspaks. When I was running a 4GC Rochester on the engine I could idle it slow enough to blow smoke rings. Now that was cool!

Sorry Chester.

Stu Fox