[mjfitzz]

I have a '67 Bonneville wagon with 100% stock 400 4 bbl, TH400 w A/C. Idles great, both in Neutral and in Drive. In Neutral, the engine revs freely. When it's in Drive, ANY throttle stalls the engine like blowing out a candle and causes a crisp backfire out the carb (stock Carter AVS). This problem surfaced as a stall on drive-away from a stop, but beforehand the car ran like a champ - no issues.

After exhaustive checking (timing, dwell, vac advance, vac leak, voltage, choke, idle mix), the ONLY problem I discovered was that the weight on the 2-piece harmonic balancer assembly was loose to the point where it was not turning with the engine. Is this the culprit of my stall?

[68 Firebird]

if the balancer has slipped how can you verify accurate timing?

sounds like timing or timing chain may have jumped a tooth.

[mjfitzz]

Thanks for your reply! This car has the old style 2-piece balancer/pully assembly that goes with pre-'68 water pump/timing chain cover assemblies on Full Size Pontiacs. The assembly consists of a hub, which is Woodruff-keyed to the crank and has the timing marks. So, the timing marks can't move relative to the crank. I di check though and the timing chain is right on the dots. This is how I found the loose inertia ring.

[68 Firebird]

learn something new everyday!!! I am using the later style on my 68, with the rubber ring.

back firing up out of carb that seems like ignition though.

Good Luck

Gerry C

[hal101]

I would check accelerator pump in the carb

[Pontirag]

Originally Posted by hal101

I would check accelerator pump in the carb

Ditto.

Check everything but your description is classic accelorator pump failure

[mjfitzz]

Ah haa! Thank you all for the advice. Rookie mistake by an old dog.

[lust4speed]

If the accelerator pump checks out ok, then I would check the continuity of the wire from the points to the negative side of the coil. It took me awhile to chase down that problem many years ago. If there is a break, it will be in the loop inside the distributor between the points and the grommet where the wire goes out of the distributor. Sometimes these wires last forever, and sometimes they fail. When you rev the engine in neutral there is no load and the advance plate hardly moves, but when you accelerate from a stop the vacuum drops and the advance plate pulls on the wire. If there is a break, then this motion will separate the copper strands and create an open. The plastic insulation on the wire will effectively hide the problem.

[mjfitzz]

Thanks for weighing in on this! Funny yu mention the point to coil negative wire, because intitially I was certain this problem was in the distributor. So, I have already swapped out the coil and distributor from another good running '67, yet the problem is still there. The carburetor is also a fresh re-build - so that's why I was ignoring fuel as a possible cause.

What do you think about this angle: In '67, they used a resistor wire instead of a ballast resistor. Could a fault in this wire be causing my issue?

[lust4speed]

Probably not the resistor wire since the engine would lay over both with and without load.

A fuel problem will show up as a situation that can be altered somewhat by playing with the gas pedal, while electrical is usually a much more exact drop that won't be altered by playing with the gas.

I would gather that since this is a load situation, that you could duplicate the failure by simply locking down on the brakes and torquing the engine up. If this is true, then get your timing light out and hook it up and set it somewhere secure so you can see the flashing from the driver's seat. If the light drops out just as the engine dies, then you've isolated the problem to electrical. If the light continues to flash when the engine dies, then it pretty much has to be fuel.