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Finally got my instrumentation installed. It's a Zemco fuel computer (I have carb engine)
I'm slowly getting the calibration quite close to reality, and after a few days of driving I'm surprised what this instrument is showing.
The faster I drive the better the mpg!?
At 40mph (65km/h) its appr. 24mpg (1800rpm, highest gear)
At 70mph (115km/h) its +30mpg (3100rpm , highest gear)
Coasting neutral did not improve (instant mpg)readings. With gear engaged its even worse.
I really was convinced that slow speed always gives you better mpg, but maybe this does not apply with older cars.
I have already read topics here about the BSFC charts and about the optimal piston speed and so on, but I will not give up yet.
There are few things that could be the reason:
-The fuel flow sensor is maybe not accurate at low load. Mechanical fuel pump will not give even flow. It pulsates back and forth. I need to make a slow test drive with a separate fuel canister to measure used fuel accurate.
-A/F ratio tends to be rich at idle and small throttle openings. I already have the smallest idle jet that can be found. If I bleed more air to the intake the idle rpm goes higher.
-Ignition advance could be higher at low load. I think I'm far away from the knocking treshold. I cannot add static advance any more, since that causes hot start problems. Maybe an adjustable vacuum advance canister would help.
It would be SOOOOOO easy with programmable fuel & ignition system like Megasquirt. Just put new values to the map and go for a test drive.
But for some reason I like to keep this car old and mechanical.
Any opinions?
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