Fuel economy woes

P

pdxgeo

True Classic
My 73 128 wagon (SplitPea) has been averaging about 16mpg in town driving. While i know city driving and my heavy foot will affect economy I feel that 16 is pretty dramatic so Ive been troubleshooting to try to figure it out. So far ive swapped the fuel hoses as I felt there was a leak somewhere, had the tank blasted and flushed, adjusted timing (it was 20 degrees too advanced according to Hawthorne Auto), adjusted the carb (it was running very rich, I had Hawthorne check it on the DEQ machine), swapped the primary idle jet to .050 (it was .060).

So far the MPG does not seem improved but I will have to collect a few weeks worth of receipts to do some math.

Am I missing something simple that could be contributing to the dismal economy? I LOVE the car but this is becoming very frustrating and costly.

I plan to check the rest of the carb jets/tubes etc compared to factory specs and if anything is oversized I will go back to spec.

Any thoughts or ideas would be greatly appreciated.

George
 
Excessive brake drag? Clogged exhaust? Retarded ignition timing? Too much weight in the car?
 
How can I test for brake drag? Thats crossed my mind but i forgot to mention it to Jim at hawthorne...
 
The simplest way is to put the car on a lift and then freewheel the wheels by hand, seeing if the amount of pressure to turn the tires is uniform between left and right sides.

Another way is to put the car in neutral on level ground and push it and see how much effort it takes to move the car. Or when you're driving and are stopped at a signal, see if the car wants to coast on it's own.

You can also measure rotor temps with a laser temp gun to see if any wheel has generated more heat than another, indicating drag.
 
Jack up one side/corner, spin wheel by hand. Should spin freely; often a dragging brake can be heard as well as seen to slow the wheel.

Other things that affect mileage:
Tire stickiness, profile
Tire pressure
Alignment
Engine timing
General tune (misfire)
Transaxle gearing
Thermostat
Exhaust blockage
Heavy loads
 
I had a similar MPG issue a few years back with my own 128 (from 25-30mpg down to 20-22mpg). After checking all of the issues noted by others above (+ a few more), doing the old "push the car by hand" test (both forward & backward) it felt far too difficult to move than I'd expected. Turns out my rear wheel alignment (toe-in) was WAY out of spec, creating a sh#tload of drag going forward. Set it back to spec & MPG improved, as did handling (especially on bumpy roads).

Front toe settings can have a similar effect, but bad settings here are usually more noticeable because the car will be "darty" (always trying to change direction left & right) when driving at speed.

Dragging front brake caliper(s) can also be an issue if the slider-wedges are dirty & ungreased (so the caliper can't move side-to-side). The IR heat gun test noted above (or simply using your hand on each wheel) can help here without having to remove the wheel(s) first.
 
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