Gasser troubleshooting question

[kerry]

I know I'm violating two important social boundaries here. This is a question about a vintage gasser, so please excuse me. But, there are a lot of good diagnosticians who post here, so I'm expecting stellar advice, even though it's not a diesel question.
The last couple of times I've gone to start my 74 Olds Custom Cruiser, carburated 455, it's had a pool of gas on top of the intake manifold. A cursory examination revealed that it does not look like the gas line to the carb is leaking. What could be causing this pool of gas. A stuck float? How is the gas getting outside the carburator rather than running inside the intake? It may also be running inside the intake because it acted as if it was flooded when I tried to start it today. Any insights appreciated.

[Jetmugg]

Quadrajets are notorious for "internal leaks". If my memory serves me properly, there are 2 plugs in the bottom of the "top half" of the Q-jet which are just pressed in. This is most likely where your leaks are. The widely accepted fix is to use 2-part epoxy to seal these plugs after rebuilding the carb. Get yourself a copy of a Rochester Carburetor manual, it will detail the exact procedure.

SteveM.

[leathermang]

If you do a search on Google for ' 74 oldsmobile quadrajet' you will probably find a forum of guys with the same problems and lots of answers...

[psfred]

Check the evaporation hose for holes -- you may have gasoline boiling in the carb on shutdown, and if the hose is bad, the gasoline will pool on the intake. Also check the fuel line for leaks!

You may have a sticky float (or a sunk one, for that matter) allowing the carb to overfill, causing spills. It will be hard to tell on that car, they got stinky milage anyway.

Check for traces of dye residue on the top gasket, they often leak (Q-Jets warp terribly).

I would recommend a rebuild, it's fairly easy IF you follow the post assembly directly EXACTLY (else you never get all the linakges working properly!). A rebuild will cure all the leaks, get you a new float valve seal, and let you draw file the base flat again so it doesn't suck air around the gasket.

I don't remember if a 74 has the tamper-proof plugs that everyone chisels out (why I don't know, you shouldn't need to adjust the factory mixture setting anyway) -- this usually puts a bulge in the base so they leak air.... grrr.

You definitely need to fix this, else the car will probably catch fire!

Let me know how this goes, I'm usually pretty good at getting a Q-Jet to work reasonably well, excopt for going way rich on sudden throttle opening, a design flaw.

Peter

[kerry]

I knew there'd be a wealth of information in your minds. Thanks. Did the google search and immediately hit on a site that describes the rebuild and talks about epoxying the leaky plugs. I'll have to think about whether I want to rebuild it or just buy a rebuilt one. I've had the car for 10 yrs since it had 48k on it and it has never run right between 3/4 and 7/8 throttle. It has always stumbled in that range. Up to 3/4 throttle it's fine and wide open it's fine. I put a rebuilt carb on it about 4 yrs ago and it did the same thing.

You're right about it being dangerous. As soon as I saw that pool of fuel (2 cups or so) I shut it down and I'll fix it before driving it. I use it mostly for trips to Home Depot for large items and towing my sailboat. Fuel is too pricey to use it for much else.

[psfred]

The stagger at 3/4 throttle is because it has mechanical secondaries, which open at that point, but vacuum controled air valves that stay closed, resulting in vast quantites of fuel getting sucked out of the jets. Blows black smoke at the same time. Stupid design, and I don't think you can "twiddle" it out on some engines, either -- the carb is actually much to large for that engine for one thing.

A "big" rebuild kit is gonna be on the order of $50, why on earth would you buy another problem carb?

Check the base for flatness while you have it off. I've never seen Q-Jet with a flat base once installed, you will have to draw file it flat again, and go EASY on the base to manifold bolts!

To draw file, lay a good sharp bastard cut mill file flat on the base of the upside down carb (GENTLY clamped in a vise if you prefer). Hold the file on both ends between thumb and little finger with the rest of your fingers resting on the center of the file. Press gently on the center only, just enough for it to bite (a new file works best, obviously), and file from one edge to the other. Do not press on the ends and never let more than half the width of the file get off the base surface. Cut front to back, then side to side, then corner to corner for a couple passes at a time -- high spots will show up at once. File ONLY until there are no large areas the file hasen't touched -- stripes or spots several mm big are fine, you only want to eliminate bent ears and major warping that will prevent the gasket sealing. If the tamper resistant plug has been improperly removed, you may have to file a bit more at the front to get the base flat. If the plugs are still in there, leave them alone. If you MUST remove them, drill a small hole, screw in a sheetmetal screw, and use that to pry the plug out, not a chisel.

Peter

[TwitchKitty]

I have had good luck rebuilding quadrajets. Never did have much luck with Motorcraft, that flat spot above idle was usually there to stay.