Engine suddenly running terrible

[ourkid2000]

Morning folks, I could use some advice. My 66' Toronado was running awesome until yesterday and I'm kinda lost trying to figure out where to start.

Quick backstory: I got my rebuilt QJet back from the rebuilders a couple weeks ago and I installed it on the car with no problems and, I have to say, it has never run better after putting that carb on. Quick start ups, the throttle felt snappy and smooth, and the choke was working perfect, pulling off almost exactly on the money......great right? Well a couple days ago I started up the car in my garage just to give it a quick run (not out for a drive, just a quick garage start-up) and, again, it ran perfectly. Smooth, snappy, etc. I shut er down after about 5 mins and that was that.

Fast fwd to the next day and I had just received a replacement vacuum driven headlight actuator which I was going to throw in and see how the headlights performed. I installed it, but accidentally left one of the vacuum lines off (the little actuator on top that releases) and when I started the car it kinda revved a bit too high and when I kicked off the fast idle it started to fall on its face. I realized I had left a vacuum line off and I reattached it. Since all this happened, the car has run like absolute dog s***. Perhaps all that is unrelated and something else has happened, I don't know.

Anyway, the car starts up alright but it's wanting to die all the time. You give it gas and it stumbles like crazy and it kinda reminds me of my old snowmobile when it would run on one cylinder rather than two,.....just seems lifeless or something. It sounds off, not smooth like before. I did notice when I pulled the choke over to the near-closed position that it smoothed out a bit and revved up.

So, what have I tried so far? I wanted to rule out fuel delivery to the carb so I watched for the squirts of fuel from the accelerator pump. Two strong streams of fuel coming out so that's good. I also hooked up a fuel pressure test rig and started the car. The PSI ranged from 7-9 roughly depending on throttle position, so that's not ideal but ok I think. I also capped off the vacuum port that feeds the headlights and HVAC system, just to rule out any vacuum leaks in that system. Still the same result.

Anyway, I'm pretty new to this and am learning as I go. I was going to have a look at the ignition next......just to check the timing, clean the points, swap in a replacement condenser. I actually had replaced the points and condenser about a month ago and it was running great since then. Maybe something going on there? God, I dunno guys....I'm pretty lost. I really don't want to crack into my freshly rebuild carb!

[Mudsport96]

Well, since all of this started AFTER the headlight actuator install. I would unplug it and cap off the vacuum line going to it. Then start the car and see if there is a difference. Everything you described tells me the air/fuel mixture is wrong. Especially the part about closing the choke stabilizing the idle but making rpm increase. You are reducing airflow at the carb and adding fuel... so somewhere you have enough air coming in to burn the extra fuel. And what was the last modification done? Vacuum actuator for the lights.

[ourkid2000]

Yeah, I did mention that I capped off the line that feeds the headlights vacuum and the HVAC system to rule out anything there. After I capped the manifold fitting it still ran the same. I've double checked the rest of the vacuum lines and I don't see anything off.

Yeah the last thing I did was replace the headlight actuator on the drivers side. The day before I was running the car and it ran absolutely tip top.

[Cliff Ruggles]

The symptoms sound like a vacuum leak someplace.  I would investigate further.  Might want to remove the carb and check the gasket(s) under it.  Not sure if your set-up uses exhaust gas to heat the carb but if it does it may have developed a leak there.......

[ourkid2000]

So this randomly resolved itself, it seems.

What did I mess with? Well, the only thing I played with was the PCV hose to hook up my vacuum gauge. I reconnected the PCV hose and it seems to be running tip top again.

Cliff, is it possible for the carb gasket to have an intermittent vacuum leak? I would guess not but you never know?

[Cliff Ruggles]

The PCV system is a controlled vacuum leak.  Not a good place to disconnect or tie into for a vacuum gauge either.....

[ourkid2000]

Very strange. This issue has reappeared once again.

Yesterday I had the car up and running and warmed up. Then I adjusted the mixture screws to max vacuum. It seemed to be running great, the vacuum was up around 19" and running smooth.

Started it up today and it seemed to be running pretty good when it started up but when I backed it out into my driveway I could feel an off idles hesitation but it was still running alright. I let it warm up in the driveway for a bit and it just seemed to get worse and worse. Sure enough, it started to behave exactly as it had before.....running terrible, barely idling, low vacuum (13-14") and a terrible stumble when you give it gas. It seems to try to rev up if you feather the gas a bit and you can almost hear it clear up until it starts to die again. It almost sounds to me that a bunch of cylinders aren't firing.

I adjusted the mixture screws back in and then out 3 turns but it made no difference at all. Note that my vacuum gauge is attached to the port that runs the headlights so I think I can rule out a leak in that system.

The choke was completely off as well when it was warmed up (butterfly was completely straight up).

[77cruiser]

Wonder if you have some dirt that plugs an idle tube.

[Kenth]

Have the leaking bottom plugs in float bowl been fixed?

[Cliff Ruggles]

One of the reasons I do NOT like 65-66 Q-jets.  The "conversion" for them from the original parts to a N/S assembly and blocking the bypass to the fuel bowl is problematic.  If you can't find any problems elsewhere like a vacuum leak or sucking fuel from a leaking bottom plug (all of those leak and what gave the Q-jet a BAD reputation for that issue) take a gander down into the carb while it's acting up and see if the fuel level is getting too high.  You can usually see the fuel migrating up to the gasket surface where the secondary metering rods go thru it.  It could be cutting fuel off and low fuel level as well which is more difficult to determine.

I'll also add that 100 percent of those units I've taken in for problems was leaking at the bottom plugs and most were also leaking at the bypass plug allowing fuel to enter the bowl and they would load up at idle.  For this reason I stopped using the plus and "O" ring and started filling that entire passage with lead and sealing it off permanently.  I'm probably helping out some of the folks who rebuild those but absolutely and for sure the bypass plug is USELESS for that purpose.

What happens, and it happens quickly is that the "O" ring seal things off when first placed in service, then fails after being in contact with fuel.  This can take days, weeks or even months but they ALL fail sooner or later. 

Not sure if that's what's happening hear but that issue will rear it's ugly head sooner or later.  Those carbs also develop leaks at the lead plug under the fuel filter housing which mimics a gasket leak at the housing typically causing the owner to over-tighten the nut and strip out the threads, which weren't that great right to start with. 

Not trying to put a big black cloud over your project, but if I owned a vehicle that used one of those carburetors I would amputate it off the engine and shelve it permanently and go to a 1969 or later side inlet carb with all the factory upgrades.  I've done that for hundreds of customers over the years who struggled with those early units and that move ended ALL of their issues once and for all.....FWIW......

[ourkid2000]

Thx Cliff.

Jeez, I just got this thing back from the rebuilders......like it's had fuel in it for a month, tops. I only buy the non ethanol Premium that is available near me.

[Cliff Ruggles]

Avoiding ethanol is NOT going to help.  Those POS "O" rings on the drive-in bypass plug are ALWAYS leaking when those carbs show up here (at least WAY back when I took them in). 

I wouldn't touch one these days with a 200' pole, simply because they have fundamental issues that are difficult if not near impossible to get past.

The secondary dampening system is HOPELESS, and why all Q-jets got the BAD reputation for "bogging" when going to full throttle.

The fuel inlet valves were HOPELESS, and why the factory very quickly went to a screw in N/S assembly by 1967.  Ya, I know and before someone slams me they continued with that design into 1967 on a few part numbers, but not too many.  The replacement N/S assemblies to "upgrade" the inlet valves and block the bypass are WAY too small to allow enough fuel into the bowl with high HP set-ups. This fundamental issue is why ALL Q-jets get an undeserved reputation for NOT liking high fuel pressure and float bowl "too small" for high performance use.

Those carb leak at just about every lead or brass plug in them, another issue corrected by 1969 when the factory made the castings thicker and pressed in aluminum plugs and swaged over them.  This fact has EVERYONE on every Forum, blog, etc telling you to smear a bunch of JB Weld over bottom plugs that were NOT leaking in the first place on the 1969 and newer units.

The poorly located hinge pin is HORRIBLE for fuel control and upgraded in 1969 to a far superior design with a much smaller float.  Folks that "rebuild" early carburetor with the short hinge pin are STOOPID enough to still use brass floats in them, see it done all the time.  HOPELESS scenario there no matter what anyone tells you.

Even with all that said with enough effort, correct parts and knowledge of the shortcomings of the 65-66 Quadrajets you can get them to work OK with enough effort.  They are NEVER going to be nearly as good as a later unit, difficult if not near impossible to keep up with anything making big power or a fast vehicle, but for a daily driver to and from Dairy Queen or a local car cruise you'd be OK with one.......FWIW.....

[ourkid2000]

Thx Cliff,

I get it, these carbs aren't great I know, but put me in the Dairy Queen category.

Doing what you suggest with a later carb is no small venture. That's a $1000, minimum operation and I'm just trying to get this car back on the road. One thing at a time right? Maybe in a couple years I can get a fancy new carb built for me, but not yet. I've got some body work and a paint job to do which is probably going to come first.

Also, I've got 2 1966 carbs for this car and I will soon have the better part of a 3rd carb so between the three of them, I should have something that will work. One of your colleagues has put together a 66' air horn/float bowl combo for me with all the major flaws addressed. I'm pretty pumped about this and I can't wait for it to arrive.

In the meantime, I have a serious intermittent running problem that I'm having issues narrowing down and I'm really not sure where to start.

[ourkid2000]

Have the leaking bottom plugs in float bowl been fixed?

Yes they were sealed up by the rebuilder back in January.

[Kenth]

Yes they were sealed up by the rebuilder back in January.

By "fixed" i mean, did they knock the brass plugs out, thread the holes and installed threaded plugs with some thread sealer OR did they put on some epoxy around the leaking brass plugs (short term fix that will never hold up for long).