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Tune up for modern gas: Do you still go by the factory specs, or no?

Started by 64\/54Cadillacking, July 03, 2016, 08:44:28 AM

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64\/54Cadillacking

A quick question to all of you. Do you tune your Caddy based off the shop manual, or do you tune it by feel?

I wonder how accurate we have to be in order to get our cars to run just right due to modern gas being so different compared to the old days. For instance on my carb which is a Carter AFB, I have to enrichen the idle mixture screws a good 4 to 5 turns out in order for the engine to idle smoothly. That seems crazy I know, but I believe because the gas in CA is less potent and has it's own chemical mixture compared to the  rest of the country, do you think this might have something to due with the change in the way these big block engines are supposed to be adjusted?

The old leaded gas was thicker and not watered down, so the carbs didn't need much gas to richen the mixture. Plus since Cad engines had a lot of power and high compression, the richer mixture made the engines run a lot better.

Also the float levels in the carb have to be altered somewhat including the timing being slightly more advanced to run smoother.

Any thoughts?

Thanks.
Currently Rides:
1964 Sedan Deville
1954 Cadillac Fleetwood 60 Special
1979 Lincoln Mark V Cartier Designer Series
2007 Lexus LS 460L (extended wheelbase edition)

Previous Rides:
1987 Brougham D' Elegance
1994 Fleetwood Bro
1972 Sedan Deville
1968 Coupe Deville
1961 Lincoln Continental
1993 Lincoln Town Car Signature Series
1978 Lincoln Continental ( R.I.P.) 1978-2024 😞

TJ Hopland

4 to 5 turns?    What does the book say is normal?   If normal is 3 then no worries but if normal is like 1 1/2 I would be looking for a problem like vacuum leaks somewhere.

There does seem to be some brands especially their regular grades that do seem to be extra crappy.  When I was stuck with a regional brand that seemed to be bad I would go with their premium even in engines that should not have required it and it seemed to help.  I found a brand that seems to be much better now and they are expanding in my region so I buy from them when I can. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Dan LeBlanc

Tune your idle mixture with a vacuum gauge to get the highest possible reading. On my 61 with an AFB, it does correspond to about the 1 1/2-2 turns out. Im also able to get the idle down to 480 in drive.

Vacuum is about 7 1/2 degrees advanced also for the new fuel (factory is 5 degrees)   
Dan LeBlanc
1977 Lincoln Continental Town Car

"Cadillac Kid" Greg Surfas 15364

Just for conversations sake, gasoline is and has always been refined in one of at least 7 distinct processes and mixed or blended with (or without) additives to suit (previously) the manufactures wishes or to meet standards set by some entity.  Gasoline has a lower heating value of just about 120,000 BTUs per gallon +/- about 5%.
That said carburetor settings and timing were always meant as a starting point for tune-ups with fine tuning being done by the Master Mechanic at the service agency to adjust the engine in its varying condition of wear/carbon build up/and mechanical condition to result in the best performance possible.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Jon S

Quote from: Dan LeBlanc on July 03, 2016, 10:51:09 AM
Tune your idle mixture with a vacuum gauge to get the highest possible reading. On my 61 with an AFB, it does correspond to about the 1 1/2-2 turns out. Im also able to get the idle down to 480 in drive.

Vacuum is about 7 1/2 degrees advanced also for the new fuel (factory is 5 degrees)

Agree - Mine is adjusted almost identically.  The "Factory Specs" were also 1 1/2 turns out.  I don't think "modern gas" requires any adjustments to the carburetor.  "Sounds like" the OP has a vacuum leak.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

savemy67

Hello 64CaddyLackey,

I tune my 429 by "feel" with the aid of a tachometer, timing light, vacuum gauge, and my ears.  Internal combustion engines using gasoline operate more efficiently when the ratio of air to gasoline is just under 15:1.  This ideal stoichiometric ratio allows for complete combustion - generally no gasoline or air compounds remain after the combustion process (although new compounds are created by the combustion process - but enough chemistry).

The idle mixture screws adjust the air to gasoline ratio when the engine idles.  I haven't studied the cross-section of the idle mixture screws, nor the idle circuit in the Carter AFB (my 429 has a Quadrajet), but if the factory specification for your carburetor is 1 1/2 turns, and you are tripling that value, then I would think you have some other issue (a vacuum leak as TJ suggested), or the idle mixture screws or seats are so worn as to be useless when the factory specification is applied.  You can check for vacuum leaks, and or examine the idle mixture screws to see if they are in good shape.  If there is a problem, repair or replace the defective parts.

While it is possible to get "bad" gas (dirty, watery, etc.), generally, most retail gas stations' gas is perfectly fine.  If your 52-year old fuel system is not in pristine condition, you may want to inspect it.  I dropped and inspected my gas tank, repaired the sending unit, the fuel lines were cleaned or replaced, the fuel pump was replaced, and the carburetor was rebuilt.  My car starts immediately and idles well.

As Greg implied, the only difference in gasoline today versus 1964 (other than the price per gallon), is the absence of tetraethyl lead and the presence of ethanol.  Both conditions can affect combustion, but this is more important under load (knocking/pre-ignition), and can be compensated for by adjusting timing for higher RPM.  I don't think the gasoline sold in California is less potent than in other states, but the ideal tuning for your car is more a function of where your car is located (sea-level, mountains, etc.), and the specific condition of your car (carbon build-up in combustion chamber, rusty gas tank, etc.).

Respectfully submitted,
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

64\/54Cadillacking

Great info everybody appreciate it!

As a matter of fact, I have slight vacuum leak at the carb base which must have recently started since it didn't leak before. I replaced the gaskets a year ago and the carb was rebuilt as well, but I probably need to inspect to see what is going on as the mounting bolts are nice and tight. There could be some warpage at the base or a bad gasket, so this is what I am going to do tomorrow. A very well known carburetor expert locally that has been rebuilding carbs for over 40 years has told me todays gas has definitely shorten the lifespan of carbs, and it has caused changes to how he tunes them. He's even showed me 1 month old gas that was badly oxidised, browning, and was literally turning to varnish (gumming looking substance) in a glass container with sediments at the bottom of it! He always tells me, don't let your car sit too long or else this is what the engine will be sucking down. :o Lesson learned.

The idle mixture settings from the factory on my carby is 2 1/2 turns out, on the Rochesters it's 1 1/2 to 2 1/2 turns out. So yeah, it's sucking down way too much gas in order for it to run.

Also I noticed when I sprayed some carb cleaner at the intake, the engine bogged down slightly. So it's obvious I have an intake manifold leak.

I like to go by the shop manual, but each car is different, including the condition of the engine, or any modifications that have been made to it, so sometimes what works on one car, won't quite work well on another.

But the ethanol in today's gas has really caused issues for us classic Cad owners. I just hope the gaskets on the carb is still good (only a year old), and hasn't gotten eating away from all the ethanol.

I will definitely keep all of your comments in mind as I tackle these issues.
Currently Rides:
1964 Sedan Deville
1954 Cadillac Fleetwood 60 Special
1979 Lincoln Mark V Cartier Designer Series
2007 Lexus LS 460L (extended wheelbase edition)

Previous Rides:
1987 Brougham D' Elegance
1994 Fleetwood Bro
1972 Sedan Deville
1968 Coupe Deville
1961 Lincoln Continental
1993 Lincoln Town Car Signature Series
1978 Lincoln Continental ( R.I.P.) 1978-2024 😞

Dan LeBlanc

It is possible that the phenolic spacer between the intake and carburetor is cracked. 
Dan LeBlanc
1977 Lincoln Continental Town Car

55 cadi

California gas is different than normal because the gas has an additive to it for emissions, especially summer gas there is more.

Which may be why the issues.

Jason
1955 Cadillac sedan series 62
1966 mustang convertible w/pony PAC, now in Sweden
2005 Cadillac deville