Its actually an original 1973 carb on a 1973 blazer BTW...
This is pretty good. Found through the search feature:
http://67-72chevytrucks.com/vboard/s...d.php?t=483753
Needle Retaining Clip Incorrectly Installed to Float Arm
Results in: Flooding, poor idle, poor hot-start, fuel puddling in bottom of intake after shut-down.
Comments: This is one of the most common assembly problems I see on Q-Jets. GM actually issued a Service Bulletin on this subject back in the late ‘60s because GM technicians were doing the same mistake. There is a small retaining wire on the needle. The float arm has two holes in it where the needle interfaces. People think the retainer goes through the float arm holes. Fact is, the retainer slips over the rear edge of the float arm, and must not be installed through the holes. Installing the retainer through the float arm holes results in the needle and/or float jamming.
Incorrectly Set Power Piston Stop Height
Results in: Poor idle, rich idle, ineffective idle mixture screws, hesitations and stumbles.
Comments: Post-’75 Q-Jets have an easily adjustable power piston stop that determines the lowest (leanest) position of the piston. Raising or lowering this stop outside its limits will adversely affect all performance parameters of the power enrichment circuit. Pre-’75 Q-Jets also have an adjustable stop hidden under a steel cap in the forward side of the lower throttle plate.
Wrong throttle plate gasket
Results in: Poor idle, erratic idle, ineffective idle mixture screws, symptoms of a vacuum leak.
Comments: There are several different designs for the throttle plate gasket, and they do not interchange. Two common problems occur: The first problem was addressed in a GM Service Bulletin around 1971. There is a difference in the open area in the gaskets just forward of the centerline of the primary throttle holes. Some later carbs use a gasket with a larger open hole in this area. If this gasket is used on an earlier carb, you will end up with a massive, undetectable vacuum leak. The other problems with these gaskets occur due to the idle fuel and vacuum bleed holes not lining up from one design to the next. Use of the incorrect gasket can result in blocked idle fuel and blocked vacuum signals. Always lay the gasket onto the float bowl and onto the throttle plate to check the hole alignments.
Another odd twist to these gasket designs occurred in the late ‘80s. We are seeing more and more late ‘80s truck Q-Jets (non-ECM carbs) being used on musclecars, so the problems are becoming more frequent: In the late ‘80s, there is a fuel discharge hole drilled from the secondary fuel well to a small hole located between the secondary throttle holes in the base of the float bowl. Carbs with the fuel hole require use of a gasket that has NO HOLE at this location. If a standard late ‘70s or early ‘80s gasket is used with this carb, manifold vacuum will siphon fuel right out of the secondary side of the carb, discharging the fuel right out of the power brake vacuum hole location in the bottom of the carb throttle plate. You will have a massive rich-running condition, even with the idle screws completely closed (blocking all primary fuel flow) and with no evidence of fuel being discharged on the primary side.