Many thanks for the replies. I think I've followed that so far.

Reading from the master parts list - every home should have one! - the piston assembly is 160-14S and seems (by feel) in fair condition although I don't have a slotted screwdriver to remove it.

Directly below that is the step up valve assembly 149-30S. This contains a spring loaded valve which is normally closed.

Here I'm guessing because I think that there should be a connection between the two which would be the 49-89 step up push rod.

If it is, I haven't got one - which would be the cause of my problem.

I could cut a small piece of wire to test this, I think i can make a guess at the length.

So the next question is where would I get real thing?

Thers is a small hole in the base of the carb. This is the vaccum port for the valve Todd mantioned.  This hole is feed intake vacuum through a slot in the carb to manifold gasket.  If the slot is missoriented the circuit will not get its signal.  The down positio is closed held ther by vacuum, when the vacuum decreases under acceleration the spring pulls the needle out of the jet allowing more fuel. 

the other factor with this is if it not recievig its signal its open all the time leading to an over rich mixture, poor fuel mileage and possibly fouled plugs which may also be the cause of your stumble.

Quote from: martin pook on March 03, 2012, 04:20:26 PM
Hi - can anyone help me. My 33PC ticks over fine but when I open the throttle the engine tries to die and it takes a bit of wiggling the pedal to get it to pick up to higher revs for normal driving. Giving it a bit of choke helps. I've had the carb apart, blown through the jets the accelerator pump works, made new gaskets, but nothing seems to cure it and it does make the car difficult to drive. I'd be gratful for any ideas.
martin

There is a brass piston that is pulled by vacuum which opens a valve on the "power" circuit. On my '33 PD either the bore or the piston became too worn to have the piston seal well enough for the vacuum to actuate it. I had exactly the same issues coming off idle and it made drivability very bad. I ground a groove in the piston and fitted an "O" ring to make a reasonable seal around the piston. Made all the difference in the world.

Hi - can anyone help me. My 33PC ticks over fine but when I open the throttle the engine tries to die and it takes a bit of wiggling the pedal to get it to pick up to higher revs for normal driving. Giving it a bit of choke helps. I've had the carb apart, blown through the jets the accelerator pump works, made new gaskets, but nothing seems to cure it and it does make the car difficult to drive. I'd be gratful for any ideas.
martin