Good day all,

I had my 66' Toronado out for it's first drive of the season yesterday. It seems to be running ok but there's a real bad stumble when you try to accelerate any time you put your foot into it just a bit. So, I'm not talking foot to the floor kind of stuff, that would make me think about the secondary air doors, just a quick shot on the pedal at normal subdivision speeds and the car falls on its face for a second.

My rookie intuition says to take a look at the accelerator pump because it sure seems like that would be the most likely culprit. So, I brought the car home, parked in the driveway, shut it off and I watched for the squirts of fuel from the pump when operated manually. It's got a nice healthy squirt of fuel in this scenario. I know this isn't a "loaded" condition but while fooling with this I did notice I can re-create the issue. If I have the car running and I manually flick the throttle with my finger, it doesn't seem to stumble. However, if I'm sitting in the car and I flick the gas pedal, I'll get the stumble just like when I was driving around. I wondered if this is just because the pedal is able to operate the throttle much faster than I can with my fingers?

So what have I done so far? Well, I checked the dwell and it had drifted a touch to 32 degrees so I reset it to 30. I checked the timing and it looks like it's set right at 7 deg BTDC (7.5 is spec), and then I adjusted the mixture screws for max idle speed (I started with 3 turns out and adjusted them in for max idle speed).

There are a fresh set of R44S AC Delco plugs in it and a fresh set of points and condenser. Carb was re-built 4 months ago by a fairly reputable carb rebuilder out of Florida.

Any thoughts on where I can start? Maybe a vacuum leak?

 

My first thought would be the accelerator pump also. But, since the carb was rebuilt recently, I would check to make sure the air horn screws are snug....gaskets can compress initially.
Next would be to check any slack/clearance between throttle mechanism and accelerator pump piston end. What I am thinking is....the accelerator pump is not providing a little squirt when the throttle is pressed.
The secondary air valve spring would be my last choice. It is possible that it needs tweaking after the carb rebuild.
Did this just recently start happening ? Are you running old gasoline ?

 

Ok that's good advice, I'll double check the air horn screws. I never thought to check the accelerator pump shot from using the pedal. I'll have to get my camera out and see what's going on.

The car is fairly new to me and this is the first time I've had the car out this year since I got the carb back from the rebuild so, I'm not 100% on what it was doing before. The gas is fresh, non-ethanol Premium.

 

Try turning each of your idle mixture screws in 1/4 turn at a time. See if it helps, you can try it a second time, but not more than that. Your idle may be a bit too rich.

 

Can the mixture adjustment be that picky? I always thought it's more of a "as long as you're in the ballpark" kind of thing.

 

Tough to troubleshoot carb issues without the car in front of me:
Yes vacuum leak is a good place to start, Unplug all the vac lines from the carb Cap the carb nipples. Adj A/F. Then start hooking the lines up. Shouldn't see a change.
Tip in hesitation off idle is generally a lean condition. Either an air leak or not enough gas flowing through the jets.
Try 12° timing and limiting the vac advance to 8-10° Then readjust the A/F. Did it improve?

Is the carb snug on the intake and are all 3 parts of the carb screwed together snug?
Never over-tighten a carb or the air cleaner wing nut. Warpage/leakage will be the end result.
Are you confident the carbs getting good fuel pressure from the pump? (5-7psi) Filter new?

Lean test:
1. Set fast idle to 1700-2000 rpms. Ebrake on. Slowly tip the choke flap in. Does it pick up PRMs? If so the primary circuit is lean. You may need smaller-tipped primary rods,
2. Verify the float level is ~1/4" Use a nitro float not brass.
3, Order one of Cliff Ruggles accelerator pumps. They have the correct pump cup material and correct spring weight per application/ carb PN. It is possible for a pump to deliver its entire shot before the transition to the secondaries, causing a bog.
4. Which hole is the pump rod inserted into?
5. Is the choke pull-off canister working? Does it hold a vacuum?
6. Can you see the secondary AVS door drop open when going to WOT? It shouldn't. (static).

Another quick n dirty trick to confirm the lean theory is to set it rich by closing the choke a bit then take it for a ride and see if it improves.

 

I've found that it could make a difference. Perhaps not falling flat on it's face, but I believe you would notice a difference.

 

Ok, I think what I will do is make a couple Youtube videos when I get a chance. Maybe it might be clearer to see what's going on exactly.

 

Do all of this at the same time while you're under the hood.
The distributor and carb adjustments go hand in hand. Should not adjust one and not the other.
Verify the vacuum advance canister works and holds the vacuum. Verify the centrifugal weights are lubed and not rusty.
Down the road, I can suggest you get an adjustable travel vac advance canister (not adj rate)

https://www.jegs.com/webapp/wcs/stor...vacuum+advance