Need help with Series III Idling/Running. Please!

[Chippyskipper]

1973 Series III 2.25 with Weber carb. Idle jet clear. It won’t run unless adjust the idle linkage screw in, a lot. It’ll start but the carb doesn’t respond at to any adjustment of the mixture screw.. But, I pulled the vacuum line off of the brake booster, ballpark-adjusted the carb and it started right up and responded to carb adjustments. Put the line back on and it stopped. I’ve tried taking the breather cap off, with the vacuum line off, put the line back on and it stops. Same with the air intake line from the oil bath filter. I’ve sprayed carb cleaner all over the intake manifold and base of carb and detected no leaks. What am I missing?
Thanks Ken

[erik88lr]

If I'm reading what you wrote correctly the engine runs fine when the hose to the brake booster is pulled and plugged? Have you tested to see if the booster will hold vacuum?

[Chippyskipper]

No, it won’t run with the hose off and plugged. Well, it will if I crank the idle linkage screw down pretty much all the way. But then the mixture screw does nothing.

[roverp480]

So are you basically saying ,if you introduce a large air leak into the inlet manifold it runs much better?

[erik88lr]

So are you basically saying ,if you introduce a large air leak into the inlet manifold it runs much better?

If that is indeed the case it must be running way too rich, as if perhaps the carb float has sunk or fuel is pouring in for some other reason.

[jimrr]

are the air flaps in the carb operating? i've seen them on various engines get sucked shut because they have broken linkages, springs etc.