Going down the road steady-state…45…55 mph can feel engine is not smooth…it “bucks,” it’s a 62 318 poly…my 350 in my 58 DeSoto did this and I put in new condenser…fixed it. Tried it on this 318…didn’t work. Have also changed points and coil too. Still does it. Engine is not a smooth idler either. Did compression test. Range from 125-140 all 8 cylinders. Think it could need a valve adjustment? Thanks…
What makes an engine “buck?”
- Thread starter furyfever
- Start date
65sporty
Old Man with a Hat
What are the plugs and wire like? If it's more like a sharp jerk, it's probably an ignition miss caused by a spark plug or wire
Compression numbers look good. "Bucks" are related to tuning. First check for vac leaks, including the vac advance diaphram. Might be plug wires, with one or two that are "leaking" voltage? New ign condensers can be bad, too. Find an old one.
Sounds like a lean surge. What shape is the carb in?
Cartel
Active Member
usually something in the ignition. points, loose nuts on the coil wire, loose connection on the ballast resistor, maybe the ballast resistor is going. loose plug on the ignition switch.
crusty fuse...or maybe floats are too high? if the idle mixture dont do much the butterflies might be too far open. super sloppy timing chain might cause it too
crusty fuse...or maybe floats are too high? if the idle mixture dont do much the butterflies might be too far open. super sloppy timing chain might cause it too
Blusmbl
Member
Agree completely, lean usually will be a surge feel. If it's actually bucking that's more likely to be an ignition related misfire.
If you find the idle adjustment screws aren't doing anything you either have a vacuum leak or you have the throttle blades open too far.
You should be able to kill the engine with those adjustment screws
70bigblockdodge
Old Man with a Hat
Wire/tie the choke 1/2 shut, drive car. If surge/buck is gone/better it's your carburetor. Otherwise it is ignition, any new condensers can be suspect of being bad ootb or soon after
SuperDave
Member
Sounds more like ignition than carb related. A misfire or preignition (knock/ping) would "Buck", air/fuel issues are usually a surge. Preignition would also cause an audible sound. But not always. If bumping the timing (retarding) makes it go away, it could be carbon buildup on the pistons, head or valves causing it. Or too lean of a mixture can do it too.
If it were mine, I'd replace the distributor cap, rotor, plugs and wires all at once, then the ign. module/points. And I don't CARE what ANYONE says about them, I ONLY use NGK Iridium or Platinum plugs on all my motors, be they for the road or the yard. Just set it & forget it. They last 100,000 miles.
Separate the plug wires, don't let them touch. It's easy to make them with zip ties, you loop all of them loosely in one bundle, then take another zip tie in between each individual wire and sung them down. Once they're all separated by a 1/4 inch each, the main loop can be snugged down. If you do it so the "knot" of the zip is on the bottom side (facing the engine), it looks clean and professional & almost guarantees cross fire from the wires never happens. Google zip tie spark plugs wire separator if you can't visualize it by my words. It's easy, cheap & very effective.
Again, if it were me, I'd also replace every vacuum hose on the motor. Eliminate the possibility of a subtle vacuum leak causing a misfire from an old cracked hose. Just out of principle.
But that's just me. Your wallet/spouse may not agree with that approach. The beauty of owning an older vehicle means you can work on it yourself without requiring a college degree or trade school diploma. The downside is the issue of user error goes up and it's no one's fault but yours.
If it were mine, I'd replace the distributor cap, rotor, plugs and wires all at once, then the ign. module/points. And I don't CARE what ANYONE says about them, I ONLY use NGK Iridium or Platinum plugs on all my motors, be they for the road or the yard. Just set it & forget it. They last 100,000 miles.
Separate the plug wires, don't let them touch. It's easy to make them with zip ties, you loop all of them loosely in one bundle, then take another zip tie in between each individual wire and sung them down. Once they're all separated by a 1/4 inch each, the main loop can be snugged down. If you do it so the "knot" of the zip is on the bottom side (facing the engine), it looks clean and professional & almost guarantees cross fire from the wires never happens. Google zip tie spark plugs wire separator if you can't visualize it by my words. It's easy, cheap & very effective.
Again, if it were me, I'd also replace every vacuum hose on the motor. Eliminate the possibility of a subtle vacuum leak causing a misfire from an old cracked hose. Just out of principle.
But that's just me. Your wallet/spouse may not agree with that approach. The beauty of owning an older vehicle means you can work on it yourself without requiring a college degree or trade school diploma. The downside is the issue of user error goes up and it's no one's fault but yours.
Not mentioned so probably not the issue but I just want to bring up that I have had a few vehicles buck when the fuel filter was mostly plugged. Would only buck when I get up to 55ish speeds as that is when more fuel is being pulled through the system. No backfire or noises just a weird unsteady bucking feeling in the vehicle. Cheap item to replace or clean.
Just Carbs
Well-Known Member
Put a timing light on it where you can see it through the windshield, drive the car.
ynst
Member
Surging at a constant speed in high gear (like driving down a flat road at 35 mph and NOT accelerating) is a sign of timing too far advanced. It's more pronounced if you're driving a manual trans vehicle, too.
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