Vac Advance & Shutny / Jerky Cruising
Discussion
So, I've had a very slight jerk while cursing at constant throttle.
After trying a few things, I think I have finally found what is causing this.
If I remove the vacuum advance pipe from the plenum, and block off the connector on the plenum, it runs silky smooth!
I then thought the vac advance diaphragm must be cracked/leaking. So I tried the suck-test - I can hear the diaphragm moving, and it will stick to my tongue. I can also feel/see the rotor arm moving very slightly as I suck on the vac pipe.
At the plenum end the connector isn't blocked, I checked that - can blow air through it.
The vac pipe itself isn't leaking, if I block one end with my thumb, I cannot suck air through.
Any ideas why disconnecting the pipe from the plenum & blocking up the plenum connector will smooth the rough running out, when all seems to be working?
Would this point to the timing being out?
If so, what would cause the timing to go out?
After trying a few things, I think I have finally found what is causing this.
If I remove the vacuum advance pipe from the plenum, and block off the connector on the plenum, it runs silky smooth!
I then thought the vac advance diaphragm must be cracked/leaking. So I tried the suck-test - I can hear the diaphragm moving, and it will stick to my tongue. I can also feel/see the rotor arm moving very slightly as I suck on the vac pipe.
At the plenum end the connector isn't blocked, I checked that - can blow air through it.
The vac pipe itself isn't leaking, if I block one end with my thumb, I cannot suck air through.
Any ideas why disconnecting the pipe from the plenum & blocking up the plenum connector will smooth the rough running out, when all seems to be working?
Would this point to the timing being out?
If so, what would cause the timing to go out?
Yep, my car definitely doesn't have this attached.
Still no idea how removing the vac-advance from the plenum, and blocking the plenum connector stops this jerking at small-throttle inputs.
From what I understand, the vac-advance advances the timing under small throttle openings (i.e. high-vacuum).
When I suck on the vacuum pipe, I can hear the diaphragm move, and see the rotor arm move slightly (i.e. advancing timing?) so I would think this is working.
That would lead me to believe I'm not getting enough vacuum to enable this to happen?
Still no idea how removing the vac-advance from the plenum, and blocking the plenum connector stops this jerking at small-throttle inputs.
From what I understand, the vac-advance advances the timing under small throttle openings (i.e. high-vacuum).
When I suck on the vacuum pipe, I can hear the diaphragm move, and see the rotor arm move slightly (i.e. advancing timing?) so I would think this is working.
That would lead me to believe I'm not getting enough vacuum to enable this to happen?
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