Extremely Frustrating Change in Fuel Consumption

S

Slopey1939

Junior Member
Suddenly after getting 14 to 15 MPG with my 39 Ford Fordor Sedan Deluxe my mileage suddenly dropped to 7. Initially thought it might be the carburetor that gave me good service (one rebuild) for 20 years. Found out it was cobbled together from 3 carbs. Anyway, I replaced it in the event it was causing the problem with a 91-99 rebuild. Same issue with no improvement. Burning extremely rich with black soot out of the tailpipe (no smoke) and new spark plugs being black with soot after 40 miles.
Any ideas out there?
Appreciate any help,
Dave
 
Low compression will effect efficiency. I'd look at the fuel jets also and the 94 power valve.


If you feel confident on the parts and ability rebuild it yourself. Think charlieny is the goto for 94s
 
Last edited:
Tinker said:
Low compression will effect efficiency. I'd look at the fuel jets also and the 94 power valve.


If you feel confident on the parts and ability rebuild it yourself. Think charlieny is the goto for 94s
Click to expand...

Carburetor is a new rebuild. Thanks for information.
 
What air filter or cleaner are you running ? Could be partially blocked. Check your brakes that they are not dragging and are adjusted correctly. Is the rebuilt carb really rebuilt or just cleaned up with a gasket kit fitted, that's not rebuilt. Some new power valves do not seat properly and need to be faced in a lathe. Float level could be too high. Regards, Kevin.
 
Don't know where you are located? If you are in the "frozen North" it is a good time to send the carb off to CharlieNY for a rebuild. Charlie Schwednler (716) 662-9159.
Great fair and honest guy that knows those 94's... Chap
 
If it is burning rich then there is too much fuel vs air. That just about means that the carburetor is suppling too much gas or the air flow is being blocked. Might be too much fuel pressure into the carb, but odd that would occur after working ok in the past. So try it with the air cleaner removed and eliminate that possibility. If that is not it, then most likely it is a carb issue. New/rebuilt does not equate with correct.
 
If this is new problem, have you checked the ignition system? Possibly a bad condenser?

Have you also checked that the air cleaner isn't clogged up?
 
Tires inflated properly? Muffler collapsed inside? Fuel leak(s)? Dragging brakes? Dwell and timing correct? Proper heat range on plugs? :confused:

Phil Swanson
 
Ruptured power valve.
Wrong power valve.
Incorrect power valve gasket.
Warped housings allowing vac leak affecting power valve.

Just some of the many things that could cause an over rich condition.
 
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