adjustments for higher or lower altitude driving 73 eldorado

[kkkaiser]

Hi again,

i have a 73 eldorado.  I will be trailering it from montana to Mississippi,  i noticed on the engine replacement from the prior owner, that they made an altitude adjustment. 

since MT is about 5500 and MS is about 300 max,, i am guessing it will need adjacent for the oxygen differences.

What would that entail.  will that me something i need to take to the shop??  carburetor adjustment??  any idea??

[TJ Hopland]

Does it still have a stock 73 Quadrajet carb on it?

["Cadillac Kid" Greg Surfas 15364]

There doesn't appear to be a "factory" high altitude carburetor, but if the previous owner or who ever moved it to the mountains was knowledgeable they most likely had the carburetor re jetted and the metering rods changed accordingly.  I would first see how it runs down low and then if necessary have a carburetor shop re-jet and re-rod it to standard specifications, but check it out first.
Greg Surfas

[kkkaiser]

HI,, thanks for the info,, it has a rebuilt carburetor, i am guessing is the original...

i guess i will give it a go when i get back to MS,, see how it does,,what would be the result of it being not set properly,

an engine that will not keep running or sputtering or will it be more of a lot of smoke or rough engine idling.

Sincerely

[55 cadi]

Could do any of what you said, but higher altatude is thinner air so it was probably adjusted to take in more air and gas, so low altitude you may smell more gas burn exhaust.
If it idles smooth and not too high then probably fine. Factory setting is I believe 500 rpm and was in a later service bulletin in about 1956 that it should be raised to about 800 rpm because idle was too low and tend to almost stall, I might be a little off on rpm but it was raised a little higher than norm.

[Carl Fielding]

Not exactly , J. More air , yes , period. You lean for altitude , enrich upon descent to lower altitude. Down South , WAY South , I have driven sea level carbureted cars routinely at around 10,000' , with excursions to 12,000' and up to 16,000'. Just leaned out and used low octane (70 something) , high altitude gasoline. Re-set carb and changed to high octane after descent , as the road leveled  out , and enjoyed sharing normal breathing along with my car. Neither one of us ran extremely well on high. The effects of an altitude change up or down to/from 5500' are minimal , and almost , or completely imperceptible particularly with a large powerful engine. HOWEVER : As usual , The Kid , with his vast experience and education , has it dead right. DO go to a carb specialist , or if you know what you are doing , verify whether the internals have been changed , as per Kid. If the carb was simply adjusted for altitude, it can be easily enriched by re-adjustment. If it was modified , you really would want to correct it. Otherwise you could cause damage by running too lean over time. Also , make sure to verify your timing. It may have been advanced just a bit , although this is less common than mixture control. Driving in the U.S. , if I am temporarily at high altitude , say 6000' + , I simply change to 87 octane , or if I am in areas where the altitude is that high , with passes at 8,000' - 12,000' , high altitude 85 octane is available. If you feel like telling us more about your Eldo in general , I am sure most of us would like to read about it !  - Carl

[bcroe]

For checking such things I use a WIDE BAND OX GAUGE; special sensor
in your exhaust.  It might tell you everything is fine, or how far off it is. 
I have one permanently installed in my fuel injected Eldo, but they can
be put on the end of the exhaust pipe if it isn't leaking.  These gauges
were pretty expensive when I built mine in 2000, but have become
quite affordable since then.  Bruce Roe

[The Tassie Devil(le)]

Is that an exhaust gas analyser?

Bruce.

[bcroe]

Is that an exhaust gas analyzer?    Bruce.    

I wouldn't call it that; it doesn't do CO or CO2, etc.  Just OX.  Bruce Roe

[The Tassie Devil(le)]

Thanks Bruce,

I have an old Exhaust Gas Analyser here that I use when tuning my cars, especially those fitted with the Predator Carby, and I just stick the hose up the exhaust pipe and adjust the carby mixture screw accordingly.

The problem these days is that with unleaded petrol, one cannot look at the exhaust pipe colour any more to see if the engine is running rich or lean.

Bruce.

[bcroe]

This type gauge is pretty much essential for fuel injection work, but it
works on carbs too.  One advantage over past methods is the essentially
instantaneous readout.  It can show acceleration enrichment; try that
with pipe or plug color.  To get that it needs some kind of analog display;
a simple digital number just turns into a blur.  Some have both displays. 
Mine shows nothing on stich: a red bar starts growing out of the center
for lean; a green the other direction for rich.  About 1/6 second response. 
Bruce Roe

[Jeff Rosansky CLC #28373]

It will probably idle ok but may not take power well.
In the plane, we lien the mixture at altitude and then richen it upon landing. The reason for this is that if you need power and it is too lien then it will stumble.
Are you going to stay in MS? If you will be going back/4th such as a summer home, etc it may be easier to pick up a spare carb and then just switch them out when you move.
JEff

[kkkaiser]

only a short trip until February,   I remember my gumps psudoenem from my piloting days, but as you well know, there is no device to change in the car cockpit,  would be nice though,

I guess i will just give it a try when i get there.. and check back to see what adjustments ,, i did some You tubing on quadra jets,, would i have to adjust or have the two screws at the bottom to do the leaning or enriching and use a vacuum gauge..

Sincerely

["Cadillac Kid" Greg Surfas 15364]

Any "real" modifications to the carb to improve high altitude performance would have been made inside the carb, IF there were any at all.  The Idle bleed screws are only in the idle circuit, so IF the car idles correctly (and 73's were not known as the smoothest idlers due to their first use of the EGR and a "lumpy" cam shaft) see how the car's driving performance is.  Again, all the jets and rods and APT settings are internal.  Not a problem to change them IF they need it by someone who is knowledgeable about QJs.  A Quadrajet is a great carb, but if anything is not correct with the set-up seemingly impossible to cure symptoms may result.
Greg Surfas

[kkkaiser]

well, made it to Missippi,,, gave the eldo a go,, seems to do ok,, not running hot,, seems to run fine,, not missing or anything noticeable,, no smoke,, so i guess i was just a over concerned,,,