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In other words, why did the original carb designers go for a progressive linkage and not solid

if many folks claim better performance and street drivability.

There must have been a good reason(s) to go the progressive path.

From the point of view of the engine designers, what is the advantage going progressive?

Does anyone know?

TomK

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Benefits of AACA Membership.

On 3/22/2020 at 8:56 AM, carbking said:

Pumping while attempting to start is self-defeating.

 

As mentioned by others, the fuel evaporates out of the bowls. Pumping while attempting to start will give enough fuel to the engine to fire but not stay running, plus the bowls are not being filled.

 

Again, as mentioned by others:

 

(1) Fill bowls with squeeze body or eye-dropper through the vents. OR

(2) Crank the engine WITHOUT PUMPING  for about 10 seconds, then stop cranking, pump the footfeed three times, and start the engine. OR

(3) Electric pump

 

Jon


Again, many thanks to the knowledge available through this forum.
 

My ‘63 with single four bbl carburettor was always difficult to start when left for more than a few days. I used to be a “pumper”, but after trying Jon’s advice to turn it over for a few times WITHOUT PUMPING, then pump THREE times, it started and kept running today. This was after a week of sitting. 

 

Once started, it will start easily when switched off, but the initial start was always a chore!

thank you Jon!

Rodney 😀😀😀😀😀😀😀😀

 

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Ok, tried Jon's method too.  It is a lot better.  Cranking it for about 10-12 second (which is to me quite log), stopping and then pumping 3-4 times works pretty well.

 

Thank, Jon for the info.  Thanks everyone.

 

Art

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On 3/28/2020 at 4:19 PM, TKRIV said:

In other words, why did the original carb designers go for a progressive linkage and not solid

if many folks claim better performance and street drivability.

There must have been a good reason(s) to go the progressive path.

From the point of view of the engine designers, what is the advantage going progressive?

Does anyone know?

TomK

 

My guess is that the factory made the dual quad linkage progressive to prevent a huge 'bog' when the driver floored the gas pedal.  I'm no carburetor expert, but there's only so much fuel an engine can use depending at a given RPM.  The idea behind the progressive linkage is to bring on the amount of fuel the engine needs as the throttle is opened.  Even the fabled tri-power 427 Corvettes of '67-'69 used a progressive linkage, not solid.

 

Others, including CarbKing. are invited to jump into this debate..😎

 

  

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Pumps are OK.

 

"Baby you can drive my car"

Foot gas pedal Stock Videos, Royalty Free Foot gas pedal Footages ...

 

But take the pump OFF when you start it!

 

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Bernie - do tell what is the second picture?

 

Nice pumps BTW

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Yep, it is a Riviera piston. Around the turn of the century my daughter started driving. One nice Summer weekend I told her that she should know how to start all my cars. And just give her a little edge on the boys whom had less experience. When we got to the Riviera I told here "Now, this car has a choke and you have to set it before you cold start. Push the pedal to the floor and give it one pump".

I couldn't see her foot because of the console. The car started instantly and at full throttle. She turn and looked at me with one of those looks only a woman can give. And I scrambled for the key.

After catching my breath and she had gone into the house (to cry), I eased into the driver seat and cautiously started the engine. It started right up and had a knocking rattle that made me think a pushrod had come loose. I drove it into the garage to check deeper. The top end looked fine. I pulled the pan and it was full of Chickets. The lower end of the connecting rod was fine.

CHICLET BITE GUM (BULK CHICLETS) « redstonefoods.com

The upper end was rattling around in the bore, pistonless, but still running. I had been trying to identify a slight roughness but couldn't put my finger on the problem. I think the piston was cracked and she pushed it over the edge.

She is 35 now. I was talking to her last week and mentioned the car. She still calls it "The Car I Ruined".

 

So if you are going to pump, don't pump half way!

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On 3/30/2020 at 9:46 PM, carbking said:

(Fast forward to the mid-1950’s and the horsepower wars, plus the emergence of local dragstrips throughout the country. The racing sanctioning bodies often would allow internal engine modifications (camshaft, compression, etc.) but REQUIRE the use of the original carburetor(s). Thus the car manufacturers would offer twin 4-barrel setups with progressive linkage so that they could use carburetors THAT WERE TOO LARGE FOR NORMAL DRIVING. During normal street use, the engine would run only on the primary carb, and engage the secondary carb only under “spirited” street driving; BUT the larger carbs were present to provide sufficient airflow for engine modifications of larger camshafts, increased compression, etc. Street drivability with progressive linkage will never be as crisp as using solid linkage.)

 

So quoting you from your article (see above), the carbs on our 425 dual quad setup are too large to run a solid linkage setup for street use or is it the manifold design?  That makes some sense if it's the carbs.  What are the cfm's of the stocks carbs?  I ran dual Edelbrock Performer 500 or 600 cfm's with a Offenhauser high rise intake on my modified Chevy 409 with solid linkage.  Went with the smaller cfm carbs so to not over carb it, and of course it was easier to setup as a solid linkage setup.

 

Thanks,

ArtDSCF1016.thumb.JPG.7ca027f1693fc5ac90ba76b0d8e5e900.JPG

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They are 625 CFM. Marginally large, but the front carb is not calibrated to run solid.

 

The CFM is close enough on this engine that you might be able to recalibrate these and run solid linkage, especially since they are Carters, with the air valves.

 

I run two HIGHLY MODIFIED 625's on my high performance 390; but I spent a LOT of time on the carbs. Idle tubes, idle bypass, idle air bleed, all jets, step-up rods, step-up springs, all four jets, and the auxiliary air valve were modified. But it runs GREAT!

 

Jon.

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