L-jet running rich Options

[Ctrout]

I know that everyone here has D-jet but does anyone know of any L-jet gurus anywhere? My car has smelled like it runs rich since I got it. While doing some exhaust work this morning, it was confirmed by the black soot everywhere. I thought I read somewhere that these cars ran rich from the showroom floor. I have backed the idle adjust all the way out with no apparent change in the richness of the mixture. It did change the RPM to a point though. I read in one thread something about coming in from working on the car and smelling like I had been standing next to a diesel campfire. That's me!

[ConeDodger]

Wow... L Jet sure wakes people up and gets them vocal.

L Jet as I recall has a series of sensors that report conditions back to a brain and given the condition reported the mixture is either richened or leaned.
If I recall from my EFI L Jet Datsun Z days you should have an AFM which is a big flapper box reporting its flap position via resitance change to the brain, it has an idle screw that only works at idle. If the box wears out you can mess around as others have suggested tightening the spring as a loose spring will just allow the flap to swing wide open with any air flow and send a resistance signal indicating a need for richer conditions.
You have a cylinder head temp sensor that sends a resistance signal to the brain telling the brain when the engine is hot. Hotter engines need more fuel.
You have a throttle position sensor which sends a resistance signal that richens the mixture at both wide open throttle and at closed throttle.
You have a cold start injector which gives a momentary fuel burst in the intake plenum during cold starts.
You have injectors which open for a fraction of time. Think of wide open throttle as a bigger fraction of time, possibly even 1/1 or steady squirt. Think of any position on the gas pedal as a steadily increasing fraction heading toward 1/1.
You have a thermotime sensor that senses if the engine is cold and closes as it warms. This could be FUBAR.
Most problems people associate with the EFI are not EFI at all.
First of all, lean conditions are often actually vacuum leaks. L Jet depends on a known amount of air getting to the engine past a flap which reports its position to the brain. Introduce a leak and more air gets to the engine causing a greater AIR/fuel ratio. This will cause a fast idle and lean condition. Probably not your problem but lets not rule it out since you could have a rich running condition superimposed on vacuum leaks.
Second, your injectors could be all gummed up from what? centuries of use? A gummed up injector dumps fuel instead of spraying it. This bad pattern disributes fuel poorly in the chamber and it just doesn't burn as well. Clean or replace your injectors.
Low fuel pressure can result from clogged fuel filters or a weak pump. This will cause the same bad fuel spray pattern discribed above.
Electrical problems are big gremlins for EFI. Low voltage will not even allow the injectors to fire. Gummed up connectors will increase the resistance of electrical flow and after all, the brain is looking for a resistance signal.
Rule out fuel pressure and electrical problems first. Check and clean your connectors, check the resistance.
There is a fuel injection rebuild specialist in Orange County called Brett Industries. They could rebuild your AFM for about $135.00. They bench test it and preset the spring tension. I think they also rebuild Thermotime sensors.
There are a couple of injector rebuild places that clean and check spray patterns they advertise in Grassroots Motorsports.

Good luck. If your fuel pressure and electrical stuff is good, I would replace vacuum lines, have the injectors cleaned first then have the AFM rebuilt or replaced.

Rob