I have a 1987 Chevy 20 van with a 350 in it. The van starts and idles like it is brand new, but when you try and accelerate hard (put the gas to the floor to pass) it loses power, and the engine will not wind out, when you back off the gas a bit, it does start to accelerate slowly, but it only manages to get up to about 110 Km. When you put the gas pedal to the floor it bogs down like it is choking out.
Thanks Rasmataz, we replaced the cap & rotor, and also tried advancing the timing, with no difference. The van seems to run fine, until you press too hard on the gas, then it sounds horrible, not chugging or missfiring, it just bogs down and actually loses speed, it will not achieve high RPMs ( rev up) under load. As you let off the gas, at a point it will start running better and accelerating slowly.