[Christ]

Originally Posted by aussie_modder

Been mulling on this for a couple of days now.

The basis of fuel metering in a carb is dependant upon the volume of air passing through irrespective of mass.

So, if our main jet is fixed, the air/fuel ratio will vary dependant upon the density of the incoming air.

Now, why do some carb cars seem to run better in the cooler weather?
Now with my vehicle, it feels like it gets better fuel economy during the warmer months (when highway driving), which would hint at perhaps fitting a HAI. however, given the dirty aerodynamics of my vehicle, i think that this phenonmenon is more due to the warmer air being less dense, therefore less aerodynamic drag (easier to cut through) than during colder air temps.

Since the carb is not adjusting the amount of fuel to take advantage of the the extra oxygen associated with denser air, my thought is that the main jet (from the factory) is probably set to the rich side (to cater for worst case scenario) and cooler air is in effect 'leaning' out the air/fuel ratio promoting a more complete burn and giving the feeling of more 'power'.

i understand that warm air assists in atomising the fuel, however when at cruise (where i spend most of my time), but wouldnt the light load/high vaccuum conditions contribute more to fuel atomisation through the carby than warm air will? after all, most factory warm air systems revert to fresh air once the engine has reached operating temperature.

So, in order to get my a/F ratio closer to stoichiometric, the first step should be to direct air that is as dense as possible into the standard air intake? Either read the colour of the plugs or use an A/F gauge (o2 sensor stuffed up the exhaust)?

With the leaner mixture, and fitment of a higher energy ignition system, a more advanced timing profile (more vaccuum advance?) will also be possible?(lean mix takes longer to burn, but needs more spark to ignite).

Weld a bung on each side of the engine's exhaust header, and insert one-wire case-grounded O2 sensors (You can get them from Hondas before 1991)

This will give you a basis for a quick and dirty O2SAT test, which will tell you if you're inside a given range of A/F ratio.