Ok… so I know there are lots of post about this topic out there but I can’t find one that specifically addresses my situation. 1967 cougar 289 2 barrel. Starts well, runs well, can drive it all the way to my work (about 40 min hwy driving with no traffic). Return trip is when the problem happens… makes it about 2/3rds of the way home and the hesitation/stumbling/surging starts… usually about the same area as well. The best I can figure is it is a longer uphill portion of the trip (although not a major slope) and the temperature is always significantly warmer then in the morning. Could this be simple overheating? The temp gauge is usually about 2/3rds of the way to the high setting. Additional info… brand new fuel tank, sending unit, fuel pump, fuel filter, and the carb was partially rebuilt And cleaned. It goes away after a few minutes at a slower speed on the side roads.
It’s not like the engine is pinging right? Like when the distributor is a bit too advanced?
Since you mention it’s slightly uphill, pinging usually occurs when increasing the load on the engine.
My last round of surging was due to a vacuum leak. One of the vacuum caps on the carburetor was cracked. If that was the cause Idk why it would only happen in the afternoon and not in the morning, though.
At highway speeds I would think your temp would be lower. Mine drops at highway speeds due to increased airflow and then rises once I get off the highway. I have a 180-degree thermostat and my needle never goes past 1/3.
I’ll check the timing again. Haven’t looked at it since last year. Thought I had it in a good spot but worth a look. As for the vacuum leak I suspected it might be that so I used a gauge and it was pulling good vacuum at idle (about 20 on the gauge). If there was a leak would it pull good vacuum at idle?
I’ve never been sure what people mean when they say pinging… I think I can hear some kind of ticking noise that speeds up with rpm…
Pinging sounds vaguely like a coffee can of marbles rolling around in it, but muffled quite a bit. Happens more often when the engine is under heavy loads, not usually idling or cruising unless your timing is waaaay off.
I had a somewhat similar problem with my '70 351C-4V when I first got it. It ran fine until I was accelerating with a low fuel level and an upward grade. The cause was a loose fuel connection on the pump suction. It didn’t leak gas that was noticeable and ran fine most of the time. In this situation the fuel pump had to pull harder on the suction side. It did pull air much of the time, the first clue was bubbles flowing into the plastic fuel filter at idle. Apparently the carburetor could vent the air up to a point and still get enough fuel. But at times it was overwhelmed. It usually stumble or stalled in these situations but would restart after some cranking.
Just another possibility to check. Hope you get it resolved
Alright so I think I definitely had the timing too advanced. It was pushing 20 degrees which is way wrong. I turned it back to 12 degrees which seems like the limit I should do according to what I found online… I have electronic ignition. Oddly the engine does not idle as nicely as it did before. Much more lumpy. Is that to be expected? Also, I’m guessing the noise I was hearing was knocking from the advance.
Engines like more timing at idle. With vacuum advance connected mine idles very smooth at 30-40 degrees timing. If I plug the vacuum advance and timing goes back to the 10 degrees base it’s choppier and loses RPM.
Don’t know if this’ll help, but I had similar (and more) problems until I went back to my old distributor.
Then everything went great.
Seems my Cougar didn’t like the brand new Flamethrower Ignitor 1 electronic distributor we put in.
If you have the old one… give it a try and see how your engine runs.
Vacuum for the distributor comes out of the carb… when I detach it from the distributed nothing really changes. Timing is advanced the same amount. I put the vacuum gauge on the line from the card to the distributor and there is no vacuum at idle but it goes up when I rev the engine. When I read the vacuum pressure elsewhere at idle it seems decent (around 20). Is this normal?
Sounds like you’re using a ported vacuum port on the carb (takes vacuum above throttle butterflies). Try switching the vacuum advance to a manifold vacuum source (takes vacuum below the throttle butterflies). Someone here can correct me if I’m wrong but I’m pretty sure ported vacuum was only used on cars from the mid-late 70s as a means of getting cleaner emissions at idle. Your motor is meant to have the vacuum advance connected to manifold vacuum.
Well I tried attaching the vacuum advance to the manifold vacuum and it definitely improved the idle. I glanced at my dads tbirds (which I know are 390 4 barrel so not exactly a reliable comparison) and they are connected from the carb to the distributor in the same way… if I search online all I get is the mustang 289 which appears to take vacuum from the manifold. I’m so confused… anyone have a photo of the top end of a 289 cougar without an air filter in the way???