OT (somewhat) 911S 2.2l Motor maladies, Steady Throttle popping issue Options

[Cupomeat]

My Dad's 911S has an issue with intake popping while normal driving.

BACKGROUND; Engine fully rebuilt (within 1.5k miles) and valves adjusted about 2 weeks ago. Engine was an MFI engine converted to PMOs before we bought the car. (someday I dream to go back to MFI.)

SYMPTOM: Prior to the valve adjust a sporadic 'Popping" was coming from the intake as a small backfire on a regular basis.

After the valve adjust (first since rebuild), it runs better but still pops. When I go up there, I am going to check the rotor and dist cap, but anything else to check?

Sadly, the motor does not run nearly as strongly after the rebuild as it did before the rebuild (crazy, I know). The top end, just isn't there now like it was before. I don't get the needed time to spend with the car, tinkering, as I'd like to see why.

But, back to the popping, It seems to happen mostly while cruising at part throttle.

My logic says that it is ignition and that a spark plug (or carbon build up?) is firing while the intake valve is open.

Does this makes sense? David asked me if they carbs had been rebuilt, and it has been years since they have, but there are no flat spots or stumbles while driving.

Thanks

[ArtechnikA]

SYMPTOM: Prior to the valve adjust a sporadic 'Popping" was coming from the intake as a small backfire on a regular basis.

Eric's suggestions are good ones.
In addition, use a SynchroMeter to make sure the carbs are synchronized side-to-side.

Pop off both link rods and use the idle stop and (if necessary, shouldn't be) the idle air correction screws to even them up. Opinions on the idle air bleeds varies, but AT LEAST ONE must be fully closed. Some (including me) maintain that they should all be fully closed.

Anyway - get them all sync'd at idle.

Then put the linkage rods back on. If anything changed, adjust the linkage rods so that they're the same again.

Mis-sync'd induction means that one side of the engine is forcing the other side lean...

[Cupomeat]

SYMPTOM: Prior to the valve adjust a sporadic 'Popping" was coming from the intake as a small backfire on a regular basis.

Eric's suggestions are good ones.
In addition, use a SynchroMeter to make sure the carbs are synchronized side-to-side.

Pop off both link rods and use the idle stop and (if necessary, shouldn't be) the idle air correction screws to even them up. Opinions on the idle air bleeds varies, but AT LEAST ONE must be fully closed. Some (including me) maintain that they should all be fully closed.

Anyway - get them all sync'd at idle.

Then put the linkage rods back on. If anything changed, adjust the linkage rods so that they're the same again.

Mis-sync'd induction means that one side of the engine is forcing the other side lean...

GREAT Info, I have the Weber book, so I'll give it a go the next time I am up there.
I've had a lot of experience with synch of Dellortos, but none of the 3 barrel Webers like these.

So, in theory, what is causing the popping? How is the intake charge ignited to create the backfire? The lean condition is clearly bad for the car and I'll want to get it fixed asap.