Guys: '76 El Camino 350 with 400 turbo transmission. As we take off from stop and accelerate past 35mph, we get a surge in power then no power. It is like it revs, then drops. If you maintain pressure on the accelerater, it will buck or rock back and forth between power and no power. It doesn't shut down, or die, just keeps rocking until I release the accelerator and then re-accelerate, then it runs great. I told my dad, he says maybe the transmission modulator. A friend at school says carb trouble. I would be thankful for any ideas, and where should we start.

Is the trans up shifting or down shifting when you let off and then re-acclererate?

The way you describe it, I would agree with dad, maybe not the mod per say, but SOMETHING with the 400.

Have you replaced the fuel filter in the carb lately?

Carb or timing. Disconnect and plug (on the carb side) the vacuum line to the vacuum advance can on the distributor. Test drive the car, and if the problem goes away, it's the cannister. You may lose power due to the lack of spark advance, but if the engine runs steady, you've found your bug. Also, remove the rotor and check the advance weights for freedom of movement, wear on the posts, etc.. If they seem to be sticking, spray them with WD-40.

If it's a carb problem, it's a bit more difficult to diagnose without knowing what carb is on it. The fuel filter does not sound at fault. If clogged, it will have an effect moreso at full throttle. Likewise, the transmission modulator should not produce this exact symptom, but I can't completely rule it out.

With a little more info, I may be able to pinpoint your problem. You can email me through the above link if I don't get back to you through this forum, as I sometimes go for days without checking in to this site.

Steve