Installing a fuel-flow gauge?

[Michael]

Carbureted V8 (1970s style big block Chevy) S30 here, with an older aluminum fuel-cell filled with foam, and mechanical fuel-pump driven off of the crankshaft.  The engine runs OK – I think! – but the fuel mileage is atrocious. 

 

The manufacturer of the fuel-cell (Triangle Engineering) evidently no longer exists, but the unit much resembles this one, from Jeg’s: https://www.jegs.com/i/JEGS/555/15389/10002/-1?gclid=Cj0KCQjwhY-aBhCUARIsALNIC04c--8Ok-o0WtGmkpOwfZnzSK2Q5oxw3R6kGnD4y0a_MTBccgI4klgaAuATEALw_wcB

 

There is no fuel-level gauge.  It’s a single 3/8” fuel-line, no return.  Because of the foam in the fuel-cell, I can’t visually inspect the fuel level.  But upon filling say 3-4 gallons at a time, I almost invariably run out of gas after maybe at most 10 miles of driving.  By “run out of gas”, I mean that the engine dies.  Then, moving the carburetor throttle by hand, results in anemic or non-existing squirting into the primaries.  This suggests that the carb’s fuel reservoirs are nearly empty.  And yes, there’s whiff of fuel in the exhaust, as the engine almost certainly runs rich… but rich enough to get 2-3 mpg at part-throttle around town?

 

So, the question: to diagnose if the fuel is magically evaporating/leaking/going down a wormhole, or actually reaching the carburetor, I would like to have a gauge in-line with the fuel line.  Has anyone installed such a thing?  Any thoughts?  Lessons?

 

A super-sophisticated (and expensive, probably) example is here: https://www.sentronics.com/applications/fuel-consumption-measurement/ .  A janky one is here: https://www.amazon.com/DIGITEN-diesel-Liquid-Sensor-Counter/dp/B017CONTVS .

[Dat73z]

I would start by reading the plugs and inspecting the oil to ensure it isn't a malfunctioning carb issue dumping fuel into the engine, although if that was the case I'd think you would've already fouled out the plugs and have a crankcase full of fuel. 

 

I'm not sure what benefit you'd get from the fuel flow gauge, I'd think an afr gauge would be more useful. For what it's worth on a LS1 GTO I think I was averaging like 6-8mpg mostly hooning around town. Never had a carb'd big block but 2-3 might be reasonable? 

[Michael]

Plugs did get fouled, before I figured out an enormous error in the ignition timing (off by something like 50 degrees, but that's a story for another thread).  They no longer do. Oddly, the atrocious gas mileage is utterly the same, from before recognizing the timing problem, to after it was corrected.  And the 2-3 mpg is from babying the car, never exceeding maybe 2500 rpm, never spinning the tires... start off at a traffic light in 3rd gear, then at 25 mph or so, shift to 5th (which is 1:1... it's a Doug Nash 5-speed).

 

Also, there's no gasoline-smell when pulling the dipstick, either before running the engine, or after.

[Dat73z]

Maybe someone else with a big block can chime in. It sounds like you don't have any fuel leaks and your timing is good, I assume you've taken a look at all 8 plugs. 

 

Your mix could be pig rich in certain areas of the dynamic driving range, I'd recommend an AFR gauge to know for sure. I've been driving my carb turbo L6 a lot of bumper-to-bumper traffic for hours in-city and my fuel mileage is terrible, <10 mpg with as much boost as I can. On the weekends when I cruise on the freeway long-distance it can be in the 20s. 

[NewZed]

On 10/10/2022 at 4:08 PM, Michael said:

upon filling say 3-4 gallons at a time, I almost invariably run out of gas after maybe at most 10 miles of driving.  By “run out of gas”, I mean that the engine dies.  Then, moving the carburetor throttle by hand, results in anemic or non-existing squirting into the primaries.  This suggests that the carb’s fuel reservoirs are nearly empty. 

 

Lots of guessing here.  Why don't you get some actual numbers and do the math?  Fill tank, drive car known number of miles, refill tank with known quantity of gas, calculate gas mileage..