Tuning observation

[Rick Parker]

Perhaps some of you have noticed this also. We know the carbs are tempermental and operate within a narrow range. Recently we had a day with an unusual temprature spike above 100 degrees and the car did not seem as crisp and idled slower. My guess is the A/F ratio went fat. Thinking of dropping the idle fuel jet one size in that type situatuion??. What say you??

[Gaz64]

Rick,

Fairly typical of carburettors that breath only from one location.

The car makers did it better with thermostatically controlled air inlet, (a mix of cold outside air and heated air from the exhaust manifold).
The carburettor was calibrated for a higher than average ambient temperature.
Any carbed car especially race cars benefit from as cold an air temp as possible, then the carb is calibrated for that temperature.
Either side of that temp, the calibration will be rich or lean. Racers use a density meter to jet their carbs at the track from previous data collected.
Cold air is more dense, so more oxygen is available for combustion, more oxygen means more fuel needed to be correct A/F=more power.

[vector1]

I would guess the fuel is not made for the atmosphere a carb or webers see, keep it cool and have better results, percolation?

[dallas_]

I've seen that too, but if it's over 100 my drives are really short so I'm not going to worry about it.

[carmine]

Rick

I would adjust for cooler morning and evening temps.
That way you've got the right amount of fuel for that cooler denser air.
If you adjust for warmer temps you'll have to lean things out which would leave you with leaner settings for morning and evening cooler temps.
Better to run with cooler temp settings and those same settings will be little rich in warmer temps rather than running lean in cooler temps.
That richness in the warmer temps will actually help in cooling the engine.