Can't figure this out, check out video

Booster is leaking or the check valve is bad. Pull and plug the booster line and see what you have.

 

Are you saying:

1. The barrel for cyl #4 is wrongly drawing ~18 kg/hr at idle, and the barrel for cyl #3 is also at the same wrong 18 kg/hr,
or
2. The barrel for cyl #4 is wrongly drawing ~18 kg/hr at idle, but the barrel for cyl #3 is at the correct ~3.5 kg/hr?

(what video?)

 

That would be a good test.

 

A couple of things.

1. Pull the check valve and check air flow. It should only allow air to go through in one direction, (from the engine to the brake booster line). I also assume you have no problems with your brakes...plenty of boost.

2. I noticed you are using two carb meters. Reverse them and make sure one is not faulty.

3. Are the front carbs running about 3.5 kg/hr also?

4. I assume the 2 air correction screws on the problem carb are properly set, (both closed or only one partially open).

5. I assume you have properly balanced the front bank, left and right carbs with each other with the adjusting screw.

6. Did you check for a vacuum leak at the carb base and manifold? Also the lead balls that plug the holes had been know to loosen or even come out.

7. Is this a new condition for your engine? Any work done prior to this?