Plenum vacuum check flapper

I bought a sheet of phenol and hand turned a disk which has worked quite well over the past ten years.

 

At the size of this disk, it’s not going to flex, and it’s lightweight. I think thickness was something like 1mm, maybe a bit less. If I remember right, it’s what was originally used on the car. Cheap and easy to find online.

 

That cage assembly works with a pair of narrow flexible tubes connected to a pipe on the outside of the plenum, and those are frequently missing, so that may be part of your popping problem. It’s been years since I looked at that part of the system, but I remember bending my hands into awkward shapes trying to get all that hooked up.

 

when you say popping, is that through the exhaust on deceleration or snapping / spitting from the carbs?

I doubt the flapper valve is causing your issue.

Popping through the carb is a symptom of lean condition, through the exhaust is possibly and air leak in the exhaust system or intake leak. Its important to know which problem you have in order to narrow down the issue.

 

Could also be debris in the idle jets. I cleanout these jets every second year and have noticed that the car tends to pop if there is debris in them.

Best, Peter

 

Clogged idle jets is the common problem and cures most of these symptoms (8 out 10) but its not necessarily debris or fine particles causing the block, fuel is sometimes the underlying issue, especially with modern E10 fuel sitting in the fuel bowl and jets for any length of time. The jet doesnt look blocked but it is!!

Where are your air bypass screws set, they should be no more than 1/2 turn out max or ideally closed, any more and you are leaning out the mixture.

Does the mixture screws respond to adjustment, just one not working would cause a problem?

Are the accelerator pump linkages set correctly and not operating at idle, it can cause fuel to spill over.

Floats set correctly? Its vital these are set up properly as they are crucial in the correct operation of the emulsion tubes?