The Stovebolt Site Forums The Shop Area Engine Shop Power piston question.

I am rebuilding a rochester B carb I bought many years ago as a rebuilt carb for a 1954 235 truck engine. It never worked particularly well but was "good enough"

After taking it apart, it appears that the power piston may have been the problem with this carb all along. The stem is bent, and the end of the stem that contacts the check ball is mushroomed out. I am sure that the check ball could never have seated because of this.

The stem of this power piston is hollow, and there is a small hole at the base of the stem before the piston starts. I looked at some other rochester carbs I have on the shelf, and the rochester for an old 216 engine has a solid stem, as does another rochester for a 235 engine. The I also have a 1953 235 auto choke rochester, and it has the power piston with the hollow stem, but a different size hole.

I am going to need a new power piston, but now I question if the one that was in this carb was the correct one.

Would love to hear from somebody who might be familiar with the rochester B carb, who might know the difference between the solid and hollow stem power piston. Thanks.

Kurt

the solid stem piston is an aftermarket one that rebuilders use. It is sturdy but I wonder if it lets enough fuel in when it is seated against the ball. I think I have an extra one if you want me to send it to you.
George

George,

PM sent.

Kurt

Rochester illustration It looks like the hollow piston started in 1953 3.858

The ball seats in the support. The piston rod unseats it when vacuum drops.
It would be nice to know why the hollow shaft with bleed hole. Maybe it made it lighter and the bleed hole kept gas from filling it up.

As it turns out, my Carb was mis-assembled. The ball was on the wrong end of the spring. It was in the cap. The spring was ridding directly on the hollow shaft, and damaged it so that it was stuck in the support.

It would be nice to know why they wear hollow.

Kurt

I want to remind everyone that the base gasket can not cover the small hole that supplies vacuum to the power valve. If it is covered the power valve stays open giving poor gas millage.

I did that on a guys chevy II back in high school, boss showed me my screw up in front of the crusty 80 year old owner. Can't quote his words here but quite a sage!