How do you lean out a a D-Series engine? The reason why i want to do it is to increase gas mileage and. I just want to lean it out a little not enough to go to higher octane gas. Does advancing or retarding the timing do this? Obviously my car is stock except for intake so it should be safe to lean it out a little

 

reduce the amount of fuel

 

put a header and exhaust

 

If you wanted to effectively achieve better mileage per gallon, I would:

Drive line a grandma (shift at a lower rpm, don't ride the brake pedal)
Put back on the stock airbox and filter
Complete a tune up if you haven't already
Make sure tires are inflated properly
Take out useless junk in the car
Change out the fuel filter
GO ON A DIET

"Leaning" the engine may have unforseen consequences.

 

Put on header and exhaust really give better milage?? And putting stock air box in increases mileage also??????? I figure cooler air means greater amount of oxygen for each combustion so it would naturally lean a tad bit???? I know leaning the engine has its consequences, like detonation knocking but im not wanting to lean it out to that extreme. So how do i go about doing this without hondata chrome etc....... adjustable fpr perhaps??

 

You can chip your ECU and get it tuned. That may give you a slight boost in power and/or economy.

An intake, header, or exhaust can decrease economy depending on the design. If you minimize pumping losses, economy will improve. However, keep in mind that the engine and its systems have already been optimized for economy from the factory.

As stated, there are better ways to improve economy: be very gentle on the throttle, keep the tires inflated, etc.