Advice on Rochester Quadrajet Fitment options for 75 Eldorado 500 CID

[oldfezziwigg]

Hello, my 75 Eldorado 500CID GM engine came with the (new design for 75) M4MEA (A for altitude compensation) Rochester Quadrajet. The numbers on my carburetor are 7045193.

When I went to get it rebuilt, the (local shop) re-builder said Cadillac recognized the Altitude barometric compensator didn't work well and they changed the design or discontinued it in later years. The shop said they do modification for correction. (i'm leary).

MY QUESTION: Will the M4ME (the quadrajet for the 500 engine WITHOUT the "A" altitude modification) work in my 75 Eldorado? Will the M4ME mount and run efficiently on the 75 Eldorado?

The difference I can see aside from the altitude mechanism is the M4MEA electric choke has 2 vacuum breaks (one in the front and one to the rear) that interact with the electric choke to adjust the primary intake flap. The M4ME only has the front.

Also, I am not at high altitude where I live (in Massachusetts North of Boston near NH border < 100ft above sea level).

Thank you. I am new to the forum.

oldfezziwigg
T.Higgins

[benji808]

Welcome to the forum! Post some pictures of your car if you get a chance.

In my experience, the quadrajet the car came with is generally the safest bet. I'm not sure about the altitude modification (although my '75 Eldorado apparently has a California version), but I highly recommend Cliff Ruggles for quadrajet information. He has a website with a forum here: https://cliffshighperformance.com/. Post to the forum or call the number on the website and he will likely have good thoughts for you.

[badpoints]

I would let the rebuilder do the modification. Sounds like he knows what he is doing or he would of just rebuilt it with the altitude mechanism. If it doesn't work you can try the other carb. On my carb the rear vacuum break shuts the rear flaps.

[TJ Hopland]

Is there something wrong with it?  If its not broke why change it?  Have you changed anything else?  If not then it may not be happy if you start changing things. 

The gaskets for that carb still came in the rebuild kits last time I bought one.  Anyone that does carbs likely has a whole stack of them since they hardly ever rebuild one of those.   

That was the standard carb for part of 75.  Its actually got a 6th jet too.  My 75 had that carb and somehow got close to 20 mpg a couple times.  No idea how or why but it did. 

[oldfezziwigg]

Thanks to all for helpful replies.  I'm waiting in the que for the original Carb M4MEA for rebuild (supposedly long wait and expensive), I thought I'd learn all I can about options and curious how the M4ME would run on my car. I can get a complete rebuilt original Rochester M4ME for a lot LESS than the rebuild charge of the old one.  Then I rebuild the old one myself (carefully!) and I'll have a spare. I will seek out info from Mr. Ruggles site and possibly look for an index/fitment chart of Quad #s to 500 CID front wheel drive 75 Eldorados.  I never filled the 27 gallon tank recently but swear I came close 20 M.P.G. just cruising and rolling.

T. Higgins
oldfezziwigg

[TJ Hopland]

If someone is telling you that carb cost more to rebuild than a more typical carb assuming the rare parts are not damaged I would look for a new re builder.  Its got 2 extra parts and uses a different gasket that comes in the kits.  The other 95% is just regular Quadrajet.

Now if the aneroid or partial throttle jet is damaged then ya I could see it being difficult to source replacements and get adjusted.   

[jawheeler1079]

Curious what the outcome of this was? I too have the 7045193 and am also at sea level. The engine runs fairly rough and my mechanic wants to tinker with it, while I'm thinking it's easier and less expensive to purchase a rebuilt M4ME.

[Cadman-iac]

  Isn't that second pull-off he mentioned actually the secondary lockout, or dampener for the air valve?

 Rick

[Chopper1942]

I don't know about the rest of you, but my experience with rebuit carbs is not good. Everytime a customer or friend has installed a rebuilt carb, I have had to jump thru hoops to try and get it to perform correctly or meet emission standards. 

Unless there is a major component damaaged that is not available, ie: throttle body, carb float bowl, or choke housing, I would recommend rebuilding your original carb.  The kits, floats, and pull-offs are available. On the Q-Jets, I always replace the float and seal the lead well plugs with epoxy. I know the kits come with a foam gasket to seal the fuel leak, but they don't always work. When the issue arose in the 60's, GM's fix was to seal them, not another gasket.

Put a straight edge across the float bowl and air horn. Make sure they are not warped. If the carb has been off or rebuilt in the past, most "mechanics" did not torque the bolts to specs. They would overtighten them and damage the carb.

Another big issue is using the correct base gasket. Not all kits have the base gasket you need for your application. Keep the old one and compare it to the new one. Some GM applications had a thin metal gasket that went between the base gasket and the carb. If this is left out, you will have exhaust gasses going into the intake, an unmeter EGR effect.