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Rough Idle solution?

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Old Aug 2nd, 2021, 17:38   #21
bdhurley
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Originally Posted by Laird Scooby View Post
What about the hose like i advised earlier?
The hose appears to be in very good condition and seems to fit snug on the cap nipple, I will try it with a hose clip at the cap end anyway.
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Old Aug 2nd, 2021, 17:41   #22
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Originally Posted by Burdekin View Post
How have you set the idle mixture? Did it idle nice after you rebuilt the carb and reinstalled it? Did you replace the seal and bushes on the butterfly throttle shaft? What oil have you got in the dash pot?

My 71 B20A specs are 21 to 23 deg at 1500rpm for ignition.

My isolation plate between the carb and manifold was cracked and my spare was also cracked. It idled nicer after it was replaced.

It should idle lovely. I think they will always fluctuate a little with the Stromberg with the carb piston but nothing too much.
Thanks for your reply. It was a full overhaul kit from Burlen (Diaphragm, Shaft, butterfly, seals, float valve, gaskets etc. plus a new needle and jet. My isolation plate wasnít cracked but I replaced it anyway just in case with new gaskets. The needle and jet are the fixed type and fitted the needle flush with the bottom of the piston and the pressed in the new jet 2.5mm (100 thou) from the top of the internal surface of the carb. I tuned the carb by the book. The idle trim screw fully closed seems to give best idle results.

The old seals/shaft were well worn and needed replacing anyway. I could have bought the 3 special tools needed but couldnít justify the extra £100+ for a once off job. I was thinking there may have been an issue with the temperature compensator, I only cleaned it and installed it with new seals without fiddling with it.

Overhauling the carb, 123 distributer, new coil, replacing leaking break booster, new hoses, head off, cleaned & lapped valves, decarbed the cylinders, 2mm head gasket improved the idling but didnít cure it. The only thing thatís worked is sticking my finger in the hose and like magic she runs smooth and steady @ 700rpm

Last edited by bdhurley; Aug 2nd, 2021 at 17:44.
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Old Aug 2nd, 2021, 18:01   #23
142 Guy
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Quote:
Originally Posted by c1800 View Post
It appears that 10 deg timing is for B20B, and 21-23 deg is for the B20A.

https://www.volvoclub.org.uk/manuals...ualOct1970.pdf

https://volvo1800pictures.com/docume..._B20A_B20B.pdf
The uncertainty with those documents is the application to the 1972 B20A. The owners manual is for a 1971 (I recognize it because I have the same booklet in my glove box) and the Volvo green book appears to be for earlier B20A & B20B engines because of the CR listed for the B20B. In North America, the 'tunes' changed for the engines in 1972 because of emission requirements and the 10 deg at 600-800 RPM might be correct for a 1972 B20A.
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Old Aug 2nd, 2021, 18:17   #24
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Quote:
Originally Posted by bdhurley View Post
Thanks for your reply. It was a full overhaul kit from Burlen (Diaphragm, Shaft, butterfly, seals, float valve, gaskets etc. plus a new needle and jet. My isolation plate wasnít cracked but I replaced it anyway just in case with new gaskets. The needle and jet are the fixed type and fitted the needle flush with the bottom of the piston and the pressed in the new jet 2.5mm (100 thou) from the top of the internal surface of the carb. I tuned the carb by the book. The idle trim screw fully closed seems to give best idle results.

The old seals/shaft were well worn and needed replacing anyway. I could have bought the 3 special tools needed but couldnít justify the extra £100+ for a once off job. I was thinking there may have been an issue with the temperature compensator, I only cleaned it and installed it with new seals without fiddling with it.

Overhauling the carb, 123 distributer, new coil, replacing leaking break booster, new hoses, head off, cleaned & lapped valves, decarbed the cylinders, 2mm head gasket improved the idling but didnít cure it. The only thing thatís worked is sticking my finger in the hose and like magic she runs smooth and steady @ 700rpm
What did the car run like before you did the carb? What needle are you running? I replaced just the needle first off and the idle was horrible. I then fitted a adjustable jet kit so I could adjust mixture at idle, made the world of difference.

When you say you block the hose from the filler cap, did you also block the manifold nipple?

Maybe a couple of pics of your setup might help.
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Old Aug 2nd, 2021, 18:18   #25
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As a bit of a Hale Mary suggestion, try clamping the line from the manifold to the port on the distributor to make the vacuum advance function in the distributor inactive. Ignition timing affects engine speed - modern ECUs advance and retard ignition to stabilize the idle speed. If you already have some small idle speed fluctuations causing changes in manifold pressure the distributor may be picking those up and amplifying them by changing the timing which makes the speed fluctuations worse.

If clamping the vacuum line improves things, your problem may be related to the advance curve being used in the 123 distributor. You may be able to operate without the vacuum advance function with a slight sacrifice in your fuel consumption or you may be able to resolve the problem by selecting different advance setting.

Easy to do and doesn't cost anything to try.
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Old Aug 2nd, 2021, 18:59   #26
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Originally Posted by Burdekin View Post
What did the car run like before you did the carb? What needle are you running? I replaced just the needle first off and the idle was horrible. I then fitted a adjustable jet kit so I could adjust mixture at idle, made the world of difference.

When you say you block the hose from the filler cap, did you also block the manifold nipple?

Maybe a couple of pics of your setup might help.

It ran horrible for a number of reasons when I got it. The engine and trans mounts were completely gone, the break booster was whistling and sucking in air. The carb throttle shaft was worn flopping around and a carb and dripping petrol from the cold start. I used a B1CC (for 3573 carb) needle from Burlen and their rebuild kit. I fixed the cold start (choke) leak by polishing the disk surfaces and putting a small Ďoí-ring on the inside of the shaft as there was nothing in the rebuild kit for it.

By blocking the hose, I mean pulling it off the fill cap and plugging the end with my finger. There are no vac leaks on the hose or at the manifold nipple.

A smaller orifice in the breather nipple on the manifold might help, looks to be about 3mm or 4mm... maybe make a little disk with a 2mm hole and place is inside.
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Old Aug 2nd, 2021, 19:09   #27
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Originally Posted by 142 Guy View Post
As a bit of a Hale Mary suggestion, try clamping the line from the manifold to the port on the distributor to make the vacuum advance function in the distributor inactive. Ignition timing affects engine speed - modern ECUs advance and retard ignition to stabilize the idle speed. If you already have some small idle speed fluctuations causing changes in manifold pressure the distributor may be picking those up and amplifying them by changing the timing which makes the speed fluctuations worse.

If clamping the vacuum line improves things, your problem may be related to the advance curve being used in the 123 distributor. You may be able to operate without the vacuum advance function with a slight sacrifice in your fuel consumption or you may be able to resolve the problem by selecting different advance setting.

Easy to do and doesn't cost anything to try.
Thanks for the suggestion, I might explore that. I havenít played around with the other settings on the 123dist and assumed it was already tuned with the correct settings in the presets for the B20A. My current fuel economy is 26-27mpg which I think is very good considering itís an auto.
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Old Aug 3rd, 2021, 17:03   #28
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The hose from the oil filler cap should go to the air filter. Clean air enters the crankcase from the filter. If you have it going to the inlet manifold the engine sees it as a massive air leak.
The nipple on the manifold with the restrictor should route across to the side ear just behind the fuel pump. That hose should have a one way valve just above the ear. In this cross pipe there usually is a T piece that runs a hose to your servo. Check all of the illustrations in the workshop manual, hand book or what ever you have. This is a common problem. You showed evidence of it in your first post when you mention clamping off the hose from the oil filler cap.
Go back to square one and correct your hose routing.
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Old Aug 3rd, 2021, 17:36   #29
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Quote:
Originally Posted by Derek UK View Post
The hose from the oil filler cap should go to the air filter. Clean air enters the crankcase from the filter. If you have it going to the inlet manifold the engine sees it as a massive air leak.
The nipple on the manifold with the restrictor should route across to the side ear just behind the fuel pump. That hose should have a one way valve just above the ear. In this cross pipe there usually is a T piece that runs a hose to your servo. Check all of the illustrations in the workshop manual, hand book or what ever you have. This is a common problem. You showed evidence of it in your first post when you mention clamping off the hose from the oil filler cap.
Go back to square one and correct your hose routing.
Hi Derek, heís got a B20. Think a pic or two would help diagnose. This is my setup with a single Stromberg.
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Old Aug 3rd, 2021, 17:37   #30
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Quote:
Originally Posted by Derek UK View Post
The hose from the oil filler cap should go to the air filter. Clean air enters the crankcase from the filter. If you have it going to the inlet manifold the engine sees it as a massive air leak.
The nipple on the manifold with the restrictor should route across to the side ear just behind the fuel pump. That hose should have a one way valve just above the ear. In this cross pipe there usually is a T piece that runs a hose to your servo. Check all of the illustrations in the workshop manual, hand book or what ever you have. This is a common problem. You showed evidence of it in your first post when you mention clamping off the hose from the oil filler cap.
Go back to square one and correct your hose routing.
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.
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