I have a MK2 Golf 1300 engine with transistorised iginition

My engine can be hesitant/jumpy on light acceleration.

I believe the fault lies with the vacuum advance unit. If I suck on the unit it constantly lets air through, shouldn't air eventually stop passing through? or is this normal?

I removed and blocked the vacuum advance unit pipe and the engine was better, but this is not a permanent solution.

All vacuum hoses are new.