carburetor main jet screw and a/f screw - Fuel Economy, Hypermiling, EcoModding News and Forum

spyghost · 06-24-2008, 12:19 AM

hi,

i am a user of a lancer glx 2000 sohc carb engine. i tried adjusting the main jet screw and a/f screw to the lean best idle.

i would try leaning out first the main jet screw, then adjust the a/f screw to compensate. this in turn would yield to lesser fuel delivery to the intake manifold.

would it hurt the engine if i do it this way? its like i am supplying less a/f mixture to what is prescribed by the manufacturer.

Shawn D. · 06-24-2008, 07:23 AM

You could certainly hurt the engine. Are you monitoring A/F ratios in any way? Trying to make a "lean burn" engine out of one not designed for it will only result in overheating and severe detonation.

spyghost · 06-24-2008, 07:39 AM

ok, here comes the confusion, that even i am confused with...

i am still running at an a/f mixture of approximately 14.7:1 as seen from the o2 sensor and emission tests. i do not experience preignition, knocking, pinging, and detonation or any signs of engine misfiring.

what i actually did is decrease the total amount of the a/f mixture.

let's put it this way "hypothetically". let's say my engine requires 5 grams of a/f mixture that is 14.7:1 to enter one cylinder to compress and burn. by adjusting the main jet and a/f screw appropriately, i decreased the a/f mixture which is still 14.7:1 to just 2 grams. take note that the grams that i am mentioning is just hypothetical.

will decreasing the total a/f mixture (even though 14.7:1 is maintained) hurt my engine?

Shawn D. · 06-24-2008, 07:58 AM

What you're saying isn't possible. If you are reducing the amount of fuel, you are increasing the A/F ratio. It's as simple as that.

However, if the engine has a "feedback" carburetor that is adjusted by a computer, you're probably only adjusting the absolute limit, which the A/F isn't reaching because the computer has sufficient adjustment left.