air fuel mixture??

[guru1974]

Yes, I know i shouldnt have but i was tryn to squeeze every ounce of hp outta this car. So, is there an old standard setting for the screw or am i gonna have to get a CO meter?

[240260280z]

Go through this section and you should be all set.

Fuel across the rpm range is determined by the needles shape. The screw for the jet height basically sets the point on the needle at idle. However there are many things to check:

- cleanliness

- free mechanical linkage (return springs, choke/jet drop)

- synchronized linkage for both carbs

- matched needles and needle height (where it is secured in piston)

- matched jet depth

- same piston rise/fall rates

- no air leaks

http://www.classiczcars.com/forums/forumdisplay.php?140-SU-Carb-Technical-Articles

[guru1974]

oh yeah i forgot to mention i have the factory efi .........thats y i am embarassed as i found a section in the forum that says dnt touch . thanks for the quick response tho.

[240260280z]

There is a reference called the EFI bible that you should read. It explains everything.

[guru1974]

Cool, sounds good. thnks for the info. Wish i would have just left the dang thing alone, but i gotta see wat it does for myself most times.

[FastWoman]

Even after you set everything right with the old L-Jet EFI, you might find the mixture is still off. There are no intended adjustments, aside possibly for the idle mix screw at the bottom of the AFM. I don't find that it does much. You can also change the mixture by:

-- adjusting the tension on the AFM clock spring -- described in an article on Blue's Atlantic Z site. I wouldn't use this for big adjustments. This only works for low to moderate throttle. If you're really cranking the engine, the AFM will be pegged out anyway, and for RPMs above 4500 I think the AFM is ignored anyway.

-- adjusting the fuel pressure with an adjustable fuel pressure regulator. An adjustable FPR usually isn't as precise as Nissan's stock FPR, and it will not hold pressure after shutdown. You're also limited in your useful adjustment range. Again, you don't have a lot of latitude here, but the adjustment will work uniformly throughout all aspects of the EFI's operating range.

-- wiring a potentiometer in series or in parallel with the coolant temp sensor to increase or decrease the resistance of that circuit, respectively. This will either richen or lean the mixture, respectively. This adjustment will impact the mixture the same way throughout all aspects of the EFI's operating range, but it will somewhat diminish the mixture accuracy during engine warm-up.