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Rough Idle solution?

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Old Aug 3rd, 2021, 21:11   #31
bdhurley
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Hi Derek, he’s got a B20. Think a pic or two would help diagnose. This is my setup with a single Stromberg.
Mine is the standard configuration for a '72 B20A.
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Old Aug 3rd, 2021, 21:39   #32
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This depends on the vintage of the engine. Volvo reversed the direction of air flow in the PCV system on later B20s. I am not exactly sure when the change occurred; but, on my 1971 (and later) the air flow is from the air filter, into the oil separator box on the side of the engine, out the oil filler cap and into the intake manifold. Later engines did not use a PCV valve in the venting arrangement. Air flow is controlled by the all important restricting nipple in the PCV flow arrangement.

On my B20E there are separate ports for the connection to the brake booster and the PCV system (with different nipples on those ports). Later carb manifolds also had separate ports so no requirement for a Tee to the brake servo.
I'm wondering if you've hit the nail on the head and the direction of flow has been inadvertently reversed? Would explain a lot if so!

OP - could be worth swapping the hoses around so the oil filler hose goes to the air cleaner and the vac stub on the inlet goes to the oil separator (going from memory of what was on my last 140 many moons ago and the pic above)
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Old Aug 3rd, 2021, 22:01   #33
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I'm wondering if you've hit the nail on the head and the direction of flow has been inadvertently reversed? Would explain a lot if so!

OP - could be worth swapping the hoses around so the oil filler hose goes to the air cleaner and the vac stub on the inlet goes to the oil separator (going from memory of what was on my last 140 many moons ago and the pic above)
Unfortunately, the hoses are configured correctly as per the attached diagram from the service manual.

I will explore placing a metal orifice disk with a smaller orifice inside the manifold nipple which may restrict the vacuum flow whilst still function to extract gasses from the crankcase.
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Old Aug 3rd, 2021, 22:21   #34
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Unfortunately, the hoses are configured correctly as per the attached diagram from the service manual.

I will explore placing a metal orifice disk with a smaller orifice inside the manifold nipple which may restrict the vacuum flow whilst still function to extract gasses from the crankcase.
It might be right for a 1972 car but what if the car is in fact a 1971 car that was registered late or perhaps someone has changed the engine at some point in time for an older chronologically but younger in miles unit?

Also as others have mentioned the vacuum advance was changed about the same time, perhaps to coincide with changes to the PCV system that may have some influence.

Thinking back i remember my last 144 was 1972/L registration and had the later arrangement as you have uploaded. I'd previously had a 1971/K 145 with the breathers the opposite way round. When i got the L reg, i at first assumed someone had put the breathers on incorrectly and swapped them back to how i thought they should be and it wouldn't tickover properly - very similar symptoms to yours?

It seems you've tried most everything else, maybe the time now is to try the silly, stupid stuff and keep it that way?
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Old Aug 3rd, 2021, 22:25   #35
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Unfortunately, the hoses are configured correctly as per the attached diagram from the service manual.

I will explore placing a metal orifice disk with a smaller orifice inside the manifold nipple which may restrict the vacuum flow whilst still function to extract gasses from the crankcase.
The nozzle size I think is designed to be correct so I don’t think it should need to be changed.

I just can’t get my head around why taking the hose off and blocking it makes a big difference. Have you cleaned the cap and flame guard pot (pr whatever it’s called).
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Old Aug 3rd, 2021, 22:35   #36
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It might be right for a 1972 car but what if the car is in fact a 1971 car that was registered late or perhaps someone has changed the engine at some point in time for an older chronologically but younger in miles unit?

Also as others have mentioned the vacuum advance was changed about the same time, perhaps to coincide with changes to the PCV system that may have some influence.

Thinking back i remember my last 144 was 1972/L registration and had the later arrangement as you have uploaded. I'd previously had a 1971/K 145 with the breathers the opposite way round. When i got the L reg, i at first assumed someone had put the breathers on incorrectly and swapped them back to how i thought they should be and it wouldn't tickover properly - very similar symptoms to yours?

It seems you've tried most everything else, maybe the time now is to try the silly, stupid stuff and keep it that way?
I think and I could be wrong but the B18 flame trap has a NRV fitted to the intake where the B20 one doesn’t so something to check.
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Old Aug 3rd, 2021, 22:39   #37
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Pic of a B18 setup showing NRV.
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Old Aug 3rd, 2021, 22:52   #38
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The nozzle size I think is designed to be correct so I don’t think it should need to be changed.

I just can’t get my head around why taking the hose off and blocking it makes a big difference. Have you cleaned the cap and flame guard pot (pr whatever it’s called).

I’ve been through everything and it’s all clean as a whistle; the flame trap and the thing it’s attached to on the side of the block, the manifold nipple, the hoses, the filler cap.

I will try making a little friction fit orifice disk with a smaller hole over the weekend and see how it behaves. If there is no change it maybe something I have to live with. There is nothing worse than being stopped at a junction and seeing the bonnet shaking and steering wheel vibrating out of the dash... pulling out the choke to fast idle does hide it. Other than that, the car is mint.
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Old Aug 3rd, 2021, 23:05   #39
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Originally Posted by Laird Scooby View Post
It might be right for a 1972 car but what if the car is in fact a 1971 car that was registered late or perhaps someone has changed the engine at some point in time for an older chronologically but younger in miles unit?

Also as others have mentioned the vacuum advance was changed about the same time, perhaps to coincide with changes to the PCV system that may have some influence.

Thinking back i remember my last 144 was 1972/L registration and had the later arrangement as you have uploaded. I'd previously had a 1971/K 145 with the breathers the opposite way round. When i got the L reg, i at first assumed someone had put the breathers on incorrectly and swapped them back to how i thought they should be and it wouldn't tickover properly - very similar symptoms to yours?

It seems you've tried most everything else, maybe the time now is to try the silly, stupid stuff and keep it that way?
Its a very late Nov'72 (L reg) with flush door handles... must have been one of the very last to be sold as the newer facelift '73 models were already being sold in '72. Hand written in the owners manual that it cost £2,374.98 (£32,047.26 in todays money)
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Old Aug 4th, 2021, 03:15   #40
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There is nothing worse than being stopped at a junction and seeing the bonnet shaking and steering wheel vibrating out of the dash... pulling out the choke to fast idle does hide it. Other than that, the car is mint.
I think bonnet shake is a vintage 140 'thing'. On my 1971 142 the hood (bonnet) frame has a center section and at one time the hood skin was bonded to that center section with an adhesive of some sort. However, with age the adhesive let go and the whole hood skin was free to resonate resulting in different modes of drumming at different engine speeds. Quite interesting / annoying. I re attached the hood skin to the center frame with some seam sealer which eliminated the lower frequency large amplitude vibration modes. After that the sections on either side of the center frame would vibrate; but, with lower amplitude and at higher frequencies. I reduced those vibrations by applying a couple of viscoelastic pads on either side of the center frame. You can see them in the attached photo.

If you have steering wheel shake you likely have problems with the rubber bushes which hold the steering column in the column support brackets. It could be as simple as one or both of the brackets that hold the rubber bushes has come loose. The rubber bush may also deteriorate; but, when I did work on my car a couple of years ago the bushes looked to be in excellent shape. If the steering wheel is vibrating in and out on the column you have a problem with the steering column thrust bearing adjustment at the top and bottom of the steering column. Don't ignore that because the actual thrust bearing cages are out of production and if yours gets damaged you are going to be into looking for a new steering column from a salvage car.
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