[rhjames]

black smoke, chugging along and barely running points to excessive fuel.

question-does your distributor have two vacuum fittings? this makes a difference as one of them retards the timing, one advances the timing.

start over----

Timing:

when timing the engine, you can do this the old skool way, or with a timing light. I prefer old skool, but I'll give it to you both ways--with timing light and without.

remove spark plug #1, put your finger over the hole and bump engine until the compression blows your finger off the whole. stop. this will put the #1 piston at top dead center.

remove distributor cap and see where the rotor is pointing, trace plug cable #1 and adjust rotor/distributor to point at cable #1, reinstall cap and you will be close.

all vacuum lines to distributor should be plugged at this point, if you are going to use the timing light. set timing at 10 degrees advance AT IDLE. reconnect vacuum lines and you should end up with about 36 degrees total advance when you bring the engine up to 3000 RPMs. it will advance this much with centrifugal and vacuum advances in play.

If not using a timing light (old skool), connect vacuum lines properly (advance needs to be to throttle vacuum, retard needs to be to manifold vacuum). Bring engine up to 3000 RPMs (hold throttle steady) and rotate distributor back and forth slowly while listening for the highest engine speed (go one way--retard--and the engine Rs will drop. go the other way--advance--and the engine will speed up to a point then start to drop off. back up at this point). Timing now should be at maximum advance at 3000 RPMs, right where it should be.

a word of caution:

running the advance up like I do may cause detonation with low octane gas. this will break rings and pistons on the older 928 engines, as did with mine. you may want to back off the timing (retard) a little to prevent this.

once you have this completed, you can then move on to other things like why the MAF is or is not operating properly, etc......

running without the air filter (OK), and running with the filter (kills the engine) tells me you do not have enough air going into the engine, or not enough timing advance. or both.

just don't do a bunch of alterations at once. you might be blaming one adjustment for a problem and it may not have anything to do with it.

hope this helps---

--Russ