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Rough Idle solution?

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Old Aug 2nd, 2021, 15:15   #11
Burdekin
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Originally Posted by Underdrive View Post
If you've got a 123 from Amazon Cars it should have their own custom curve for unleaded (number 3 I think).
Yeah but also has the standard B20A map. I am using the B18B, like it better than the Amazon cars map.
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Old Aug 2nd, 2021, 15:19   #12
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If you've got a 123 from Amazon Cars it should have their own custom curve for unleaded (number 3 I think).
I preset 123 from Skandix and set it for B20A as per the documentation.
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Old Aug 2nd, 2021, 15:21   #13
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Where did you get the 123 dizzy from? My car is a little modified with increased compression ratio and a slightly hotter cam but it ran horrible on the B20A ignition curve. I have a Amazon cars 123 dizzy. If the other things suggested don’t make any difference try the B18B curve as well.
I got a preset 123 from Skandix and set it up for B20A (I think #4)
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Old Aug 2nd, 2021, 15:36   #14
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Blocking off the line from the oil filler cap to the manifold would result in you losing the 'positive' air flow for the crankcase ventilation system. This will result in the faster accumulation of moisture in the oil with potential sludge build up. However, most cars up to the early '60s used this non positive ventilation so it will work.

Since the crankcase ventilation hose seems to affect your problem, make sure that you have the hose connected to the correct nipple on the intake manifold. The correct nipple will have a restricting orifice in it (I think its about 1/8") which limits 'false air' flow into the intake manifold. If you use an unrestricted nipple you will have too much air flow and won't be able to properly set up idle.

You said you set the timing at 10 deg. According to the 1971 Volvo service manual the B20A ignition is set to 21-23 deg BTDC with the engine running at 1500 RPM and the vacuum line to the servo on the distributor clamped off. I don't know what the values are for a non North American 1972 B20A so perhaps confirm the correct values for your 1972 B20A. As described by others, make sure all the base tune settings are correct before trying to diagnose further.

On an off chance, since you have a 123 distributor, make sure that the advance settings are correct for a B20A . In North America the up to 1971 B20A engines used vacuum advance as opposed to retard. I don't know whether the 1972 versions continued to use vacuum advance so make sure you haven't mixed that up if you have a 123 that is programable.
Thank you for your indept reply. I've combed through my 1972 green service manual and the only timing setting all I can find is 10°BTDC @600-800 rpm for 97 octane in the specifications on page 0.9. I will try your settings mentioned abover and see how it runs.

I did confirm that the hose was connected to the correct nipple with the restriction orifice. Also add that I have a new break booster, NRV and hose.

My 123 distributor is the preset type from Skandix. I confirmed the correct setting for B20A.

The car drives okay, easily cruses at 55mph anything over that the wind noise is unbearable and its returing 26-27mpg(UK).

Rough idle maybe something I have to live with.
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Old Aug 2nd, 2021, 16:00   #15
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Check your oil filler cap and the gasket. It should be airtight.
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Old Aug 2nd, 2021, 16:50   #16
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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.
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Old Aug 2nd, 2021, 17:05   #17
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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
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Old Aug 2nd, 2021, 17:49   #18
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Originally Posted by saintlyvolvo View Post
Check your oil filler cap and the gasket. It should be airtight.
Its a new gasket and the cap goes on snug.
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Old Aug 2nd, 2021, 18:08   #19
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Renew the seal on the oil filler cap and also inspect the hose on it as well. Often the hoses perish/go soft so while they seal when cold, once warm they go soggy and let excess air in.
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Originally Posted by saintlyvolvo View Post
Check your oil filler cap and the gasket. It should be airtight.
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Originally Posted by bdhurley View Post
Its a new gasket and the cap goes on snug.
What about the hose like i advised earlier?
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Old Aug 2nd, 2021, 18:34   #20
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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
It must be a missprint on my '72 volvo service manual green book. The Haynes manual also says 14 deg @ 600-800 rpm (which would be close to 21-23 @ 1500rpm as in the owners manual)

I also found a service bulletin 20-16 issued in '74 for timing adjustments for the different octane ratings of the day. There is some interesting documents on this webpage with the help of google translate from Swedish.
http://www.240.se/litteratur/sm20-16.pdf
http://www.240.se/

Last edited by bdhurley; Aug 2nd, 2021 at 18:45.
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