Ok here's an idea.Remove vac.line at the vac.adv.and plug it off.Drive car and see if it still jerks.If not,the problem is a broken [intermittant] wire between the pick up coil and the module.It's loosing connection as the vac.advance operates.,I've seen this on H.E.I.'S.
1964 SS Impala 409/340 hp jerks bad
- Thread starter Billmac409
- Start date
You might try and disconnect the tach lead that hooks to the coil or wherever it goes on your system. I have had tachometers start to fail and reek havoc with ignitions.
Billmac409
Member
I dont have vacum advance…. Mines mechanical. Timing is set now at 6 btc but ive tried several different settings . Advance and retard both. Runs the best at between 0 and 6. I thought about changing the springs on the advance butterfly but it ran good before this problem started. I think they are the black and silver ones on there now.The tach doesn’t fluctuate when the car is jerking.
I am beginning to think it could be a fuel issue.
I am beginning to think it could be a fuel issue.
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Gliderider06
Well Known Member
I feel this is an ignition problem. Kinda like the advance weights are bouncing around under load, and settle when not. Maybe the wire lead is shorting out just enough when the advance plate moves. Ignition works differently under load vs no load.
Billmac409
Member
Mine distributor doesnt have any vacuum connection.
You said you changed spark plug wires? Did you change coil wire? I had a 283 with stock distributor and coil that acted the same way . It cut out under a heavier accel but let me get it home on a light accel. The coil wire was burning up in the ends. Also put your tranny in 2nd gear or third and set parking brake and put the engine under a load by slipping the clutch a little with a little rpm a see if it cuts out or skakes engine . You could t in a volt meter or a test probe light on ignition to see where it is braking down if it does cut out when putting engine under load. In the older days that was like putting a ignition system on a engine scope. You could also hot wire coil direct to battery and see if cutting out is eliminated. You would have to remove that wire to kill engine after that test. If engine still cuts out I would suspect the crane unit in distributor or that area.
Im gonna go with springs and rods in the carb.
Didn't do it before why would it do hard jerking now.either go rich or lean won't cause a hard buck in my opinion. Can't say I ever had a fuel issue causing a sudden jerk buck. Either they would flood run steady or no power on lean side not getting enough fuel.It would be easy to determine if it could be driven for engine miss or drive line issue. My thoughts were if engine is not cutting out period,,,,, maybe a drive line issue as carrier bearing slop, differential control arm bushings shot letting axle housing shift up and down. letting u joints bind . Broken rear control arm frame mount. That is why I mentioned power brake engine setting still.
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Easy things here to try, make sure your idle mixture screws are turned out 1 1/2 to 2 1/2 turns , and change metering rods to a smaller tipped (richer) rod, and most important here use the next step stiffer spring under metering rod piston, this will richen your ( tip in throttle response ) by allowing it to come in sooner , , and stop the surge at light cruise.
Revs fine free wheel. 1st gear bucky. 4th is fine. Tach is steady and smooth. Tires bark. the tires bark because they stop. I say the rear is binding up and unbinding. maybe internal. could be trans. 1st gear has the most torque on the drive line. 4 has little so no bind.
You are forgetting it didn't do the bucking before. How could springs and rods change ,causing bucking.
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Power brake engine setting still= engine cuts out bucks= Problem in engine.
Power brake engine again setting still ,no bucking= engine not the problem bucking.
Check rear driveline components .
That's the way I would diagnose the concern.
Power brake engine again setting still ,no bucking= engine not the problem bucking.
Check rear driveline components .
That's the way I would diagnose the concern.
The advice was for Billmac409 who first posted.
not forgetting anything , just been there and dealt with this problem before
Heres hoping he finds his problem without to much trouble
I don't see how a transition from fuel being rich to lean in a few seconds or vice versa could make a violent hard buck as he described. A ignition loss on and off fast would be more of the problem which I have encountered once .
He said it was a hard buck that almost throw him out of the seat. That's what I based my opinion on. I am sure you have had more experience since you do race for the best running . He said it never did that before so I wouldn't think a stock 1406 eddy would be a culprit. I have four different vehicles with that carb and never encountered a hard buck. .I didn't mean to pull your chain.
I've had same experience and what dm62409 is suggesting helped cure the problem. also had a similar issue with the advance weights being stuck on another engine.