Keegan

Hey, all!

I daily my '72 Cutlass Supreme, and lately it's been having some trouble, well, running. The car would hesitate sometimes and even try to stall out at stops. We've done almost everything we can think of, but we're kind of stuck right now. Any help would be appreciated!

What we've done:

• New spark plugs AND wires
• New distributor cap, rotor, points, and condenser
• Complete carburetor rebuild, including float
• New fuel filter
• Oil change
• Checked for any vacuum/fuel leaks

To clear up any questions I may get:

• Yes, the timing is set correctly
• We gapped the plugs correctly (plugs should also be correct)
• Dwell is also correct
• No crossed wires/bad connections on the coil, plugs, or grounds
• No unusual engine "knocking/ticking"

After we put the rebuilt carb (stock '72 Quadrajet) back on, the throttle feels much more responsive. However, the problem has actually worsened since. The car will fire and run well at high RPMs, but as soon as it's kicked down: extremely choppy idle and an eventual stall. It simply idles as if it has a horrible misfire.
I plan on replacing the plugs (and maybe wires) with another set to see if that fixes the problem, but if not: I'm at a loss.
If needbe, I can record a video with my phone and upload it tomorrow. Thank you for reading, I know this was a little long.

Oldsmaniac

Did you check operation of choke and choke pull off?

Keegan

Yes, both are functioning!

MDchanic

Compression test?

What kind of cam are you running?

- Eric

oldcutlass

What setting did you use for your distributor, dwell, timing, and at what rpm? What are the plugs gapped to? What brand and part number? How did you adjust the carb, vacuum gauge, tach, by ear? If you look down into the carb while its running, is there fuel dribbling? If you turn the air/fuel mixture screws in all the way with the engine running does the engine try to stall? How many turns out from all the way in are they set to now, and are they equal on both sides? Have you pulled each spark plug wire while its running to determine if a cylinder is not firing? What vacuum is the engine pulling? Just saying the settings are correct doesn't help.

oldave55

I have experienced similar problems on two different big blocks before I found the problem's source. Cam timing gear. It's my experience that the factory aluminum cam gear with its nylon covered gear teeth tends to come apart somewhere around or over 100,000 miles causing a extremely slack timing chain and a shift in timing. As I mentioned, this had to happen to me twice before I recognized the problem. Now whenever I buy a higher mileage olds that I plan to keep, I replace the water pump, fuel pump, hoses, a solid metal cam gear and chain as preventative measures against roadside breakdowns. The factory cam gear is about the only defect that I have found in the olds engine design.

Keegan

We have the tool, but haven't had the time to use it yet. Hopefully tomorrow. Also, stock cam! (whole motor is stock aside from an aluminum intake)

The plug gap is 30. They're AC Delco, R45S. As for dwell and distributor, my dad used the same numbers he has on his '72 Supreme (Sorry, I don't remember them exactly! I know he's double checked both.).
I'll fire it up tomorrow to check for any fuel dribbling! Also yes, I do believe that it tried to stall when we adjusted the air/fuel screws. I'll check those as well to see how they're adjusted, since I'm not sure. We have not pulled any plugs quite yet, but thank you for the help. I'll rack my Dad's brain tomorrow to see what I can find out. (Doing my best here, still learning!)

MDchanic

You're doing everything right so far. Keep at it and you'll figure it out.

- Eric

cherokeepeople

sure you have the correct base gasket.kinda sounds like a vacuum leak.

oldcutlass

On another note, don't assume that just because the parts you replaced were new that they are good. I've come across bad plugs, points, condenser, wires, etc.. over the years. Don't be afraid to swap in a known old part that was working to test theories. I always save 1 set of old parts and keep them around in case of emergencies and/or testing.

Keegan

Okay, just went out and fired it up. It's already running much better than it was the other day, although you can still tell it's not "100%". I opened the air screws, and it seemed to help. It only really starts to run poorly when it's kicked down, and I think I hear an intermittent "hissing" every few seconds in short periods. Could this be a vacuum problem? I'll see if I can get something to spray around the carb to check.

oldcutlass

There is a procedure for adjusting the a/f mixture screws with either a vacuum gage and or a tach. Did you get the answers to my earlier questions?

svnt442

Unplug the vacuum line from the brake booster and cap it with your thumb and see if the idle smooths out. My booster went bad causing quite the leak, but the pedal was not rock hard and caused something similar to what you are describing.

jankyrre

Does this car have a EGR valve?
What about a leak in the vacum line to the modulator on the trans.

svnt442

No EGR until 73.

Keegan

Okay so I drove it to the exhaust shop today because it's been starting to leak pretty bad. They think my manifolds are warped because the gaskets are completely burned out. We actually replaced them right after I got the car, so that sucks... maybe time to look into headers?
Anyway, the car actually backfired twice on the way home. This only happened if I really got into the throttle, though.

61reoldsman

If it's backfiring through the carb then its timing , I would agree with oldav55 that maybe the timing has skipped a tooth because of the worn nylon teeth .

Keegan

It's hard for me to tell where it's backfiring... It sounds like it comes from directly underneath me. Maybe the manifolds, where the gaskets are burned out?
I've noticed an oil leak getting bigger as well. Not sure if that has anything to do with the rest of my problems, though. (fairly certain it's the oil pan gasket)

young olds

You could pull the valve covers and watch the rockers while it runs and see if one, or more, doesn't move like the rest.

Keegan

I think I'll do that, thanks! Will update afterward.

halfmoontrail

Yours sounds like a timing or vacuum-related timing issue, the order in which you set the dwell and timing is critical.


A couple other less common problems are cracked carb base and worn distributor shaft, both can lead to these types of issues.

Keegan

It actually ran even worse on the way home. I have to put it in neutral when coming to a stop because the car will actually stall out... I think it's time to park it and go back to the Starfire for now. I'll pull the valve covers tomorrow, hopefully!

Octania

maybe you should buy my 403, it runs great. Has a rusty 85 442 around it.

Koda

Is this the self driving one?

Keegan

Well, I found out where it's backfiring! Definitely at the carb. Trying to regain hearing in my ear from that one... I suppose that narrows it down, though! I think I'll start with a timing set and see where that gets me. Will I be able to see the teeth worn out on the gear?