General Category > Quadrajet Carb Talk and Tips

Need some advice - 9 MPG is painful!!!

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Cliff Ruggles:
One problem I see is using a 160 degree thermostat.  That will hurt engine efficiency and fuel economy.  I'd put a 195 stat in it and tune the APT screw as described in our book using the stock jets and metering rods.....Cliff

86BlackBurban:
UPDATE:

Again, thank you for the wonderful help!

I got everything back together WITHOUT a power piston retainer and it runs much smoother now. Didn't notice a retainer on the old piston so chances are this carb had been opened before...hmmm...

Sorry, no power chip will help me - I'm computer-free!

Anyway, got 11 MPG on the way home which is loads better, but still have a lot of ground to cover. Looks like I may order one of Cliffs rebuild kits along with the manual...this is exactly what I was needing.

But why does a colder running temp hurt fuel economy? This was not my experience in the ricer department - seems like those smaller engines got a little BETTER fuel economy with a colder stat...Something to do with fuel atomization in a carb vs temperature? I'd love to hear your theories and I'm open to all suggestions - it's very nostalgic for me to be working with carbs again and hopefully will be more rewarding as time goes on...

omaha:
Some heat is better for fuel economy. 180-190~(more??). For all out power, maybe cooler is better but not always. Also, an original iron intake might get you a few mpg's better. Yup, the fuel stays "suspended" in the air better in its long path (comparatively speaking) to the valve. With the FI its a much shorter path and the injectors are closer to the heat source of the engine. SO...other than installing F.I., the QJ would be the closest thing to it as far as carburetors are concerned (maybe some high dollar weber setup or a 1 barrel might beat it but really...??) I think there were some other dual booster carbs design out there, maybe ford made them IDK, they might get close to the QJ for mpg.

Cliff Ruggles:
The key to best efficiency is heat, not cold.  Fuel "globs" up on cold parts, and it takes heat, pressure and spark for combustion.  You'll find the best power made right around 200 degrees engine temps, and cool/dense air coming into the engine from an outside source.

For best efficiency, get the engine hotter, it will require less fuel to do the same amount of work.

Get one of our kits, the PP retainer is standard in them, and we just added the secondary cam/spring to them as well.  Had to raise the price a few dollars, and EVERYTHING went up this year, except our wages!.......Cliff

86BlackBurban:
What are your thoughts on gently heating the fuel (110-130 degrees) vs raising the operating temperature of the entire engine? A cooler running engine keeps the incoming air more dense, and I know liquid fuel does not burn...but atomizing warmer fuel *should* be more efficient...thoughts?

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