Thread: Surging problems

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Got some surging issues happening, so I thought I'd see if you guys had any ideas.

When accelerating and cruising you can feel the car's output surge up and down and hear the exhaust rev a bit as it does it. It doesn't rev enough to seen the tach twitch much more than a hair, but you can definitely feel it.

Motor's still the stock 1983 carbed 5.0L with 192,000km (119,300 miles)... wanted to upgrade this year, but that's another story. Plugs and wires are brand new last month, fuel filter's all good (plus I added fuel system cleaner and cleaned the carb up just for the hell of it, but no change), clutch is a Centerforce II about 7 years old (about 55,000km / 34,175 miles) and still feels pretty good.

do you hear any surging at idle? might want to check your timing.

Vacuum leak? Hose with a small split in it? Vacuum advance diaphram have a hole/leak in it? Brake booster diaphram have a hole/leak in it? Sniper

It's only noticeable when you're driving, not at idle. Timing's all good.

I'll have to check the vacuum lines.
(I guess buying that vacuum tester last month is gonna be used sooner than later)

Did you mess with the mixture screws on the carb when you cleaned it up? If there are any. A lean mixture will cause surging.

Ron

Surge is caused by a lean fuel mix, or too much advance. What did you do to it just before it started surging?

I checked the vacuum lines yesterday afternoon and found a very small split on the carb end of the vac hose to the distrib... nothing that will affect anything, but I trimmed it off anyway to stop the split from going further. That was the only thing I came across.

Fuel mixture settings are all good (my marks are still lined up perfectly anyway) and the car ran great up till last weekend - I've got it running a touch fat actually because I'd rather run with a hair too much fuel than risk detonation........ maybe I'll try turning things up a bit just for the hell of it though.

As for what I did right before it started happening... nothing that I can think of. The last thing I did was replace plugs and wires, but that was about a month ago and I didn't have issues afterward. Otherwise all I've done under the hood lately is check the oil. Just for the hell of it, I even checked that all of the plugs and wires were still seated tight yesterday, but that was all good.


Truth be told, I'm kind of wondering if the motor isn't just slowly on it's way out. After all, 25 years of daily driven wear and tear (for the summer months), regardless of regular maintenance, is a quite a good life span for a stock powerplant without getting a good refresh. i was hoping she'd keep going for another year at least, but it might be time for that 331 stroker upgrade a little sooner than I had planned.

I'd try retarding the spark a few degrees. As you say, it's got some miles on it, the requirements do change over time. Also with reduced compression due to normal wear there may be slightly less vacuum draw, calling for fatter jetting. Unless you're really looking for an excuse to tear it down, I'd try to smooth it out and keep driving it. If it ain't broke, don't fix it!