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Old 04-29-2021, 04:28 PM   #1
1968 volvo
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Question HIGH rpm

Hello! I have a 1968 Volvo 142s with a B20 engine. The Carburetors were just completely rebuilt including replacing the old brass throttle shaft bushings with delrin.

It idols at 2000 rpm once it warms up. I have replaced the vacuum hoses, replaced the one way valves, turned down the idol screws on the carburetor and replaced the intake manifold gasket. None of those have done anything to help. Any suggestions on how to troubleshoot? Anything I should attack next? Let me know!!!
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Old 04-29-2021, 04:47 PM   #2
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My guess is that your intake manifold is slightly warped and after the car warms up, the seal between it and its gasket no longer seals and extra air in induced into the head.

You can try spraying carb cleaner around the manifold when it's idling high. If the idle goes down, you have a leak.
This does not work 100% of the time though because it's hard to reach all the areas.

Check that the intake mating surface is "true".
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Old 04-29-2021, 05:13 PM   #3
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Post a pic of the engine compartment so that we can see how the hoses are routed. Specifically PCV and brake booster hoses.
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Old 04-29-2021, 05:28 PM   #4
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When I swapped the weber on my car for a pair of SUs I found that I couldn't get the idle below 1500 rpm. When I went back to it I noticed two things. I had false air coming from the PCV system (disconnected hose) and the fast idle adjustment screws were holding the throttle open such that the normal idle screws did nothing. My experience has mostly been little things that I missed throwing everything off.

SW-EM has a useful diagram for sources of false air. https://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air


I would say we can rule out the throttle shaft bushings being a problem, which just leaves the carb/manifold gaskets, any hoses going into the manifold or carbs after the throttles, and the manifold/head gasket. If your B20 used to be fuel injected then you'll also have to worry about the old injector holes and whatever was used to plug them.
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Old 04-29-2021, 05:46 PM   #5
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Originally Posted by hiperfauto View Post
Post a pic of the engine compartment so that we can see how the hoses are routed. Specifically PCV and brake booster hoses.
Whats the best way to post a photo on here?
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Old 04-29-2021, 05:52 PM   #6
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Originally Posted by spock345 View Post
When I swapped the weber on my car for a pair of SUs I found that I couldn't get the idle below 1500 rpm. When I went back to it I noticed two things. I had false air coming from the PCV system (disconnected hose) and the fast idle adjustment screws were holding the throttle open such that the normal idle screws did nothing. My experience has mostly been little things that I missed throwing everything off.

SW-EM has a useful diagram for sources of false air. https://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air


I would say we can rule out the throttle shaft bushings being a problem, which just leaves the carb/manifold gaskets, any hoses going into the manifold or carbs after the throttles, and the manifold/head gasket. If your B20 used to be fuel injected then you'll also have to worry about the old injector holes and whatever was used to plug them.
The carb/manifold gaskets are brand new. And I see no signs that my car was ever fuel injected. Is there a quick way to check once and for all that it wasnt ever injected? is there a good way to check the soundness of my pcv system?
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Old 04-29-2021, 06:19 PM   #7
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just because the gaskets are new doesnt mean they cant leak. A warped surface, burr from a drop, residual gasket from disassembly, improper torque spec, improper torque sequence can all leave you with leaks. SU carbs are sensitive to a few things, so I would start what they are sensitive to, air leaks, and imbalance. Start by spraying some carb cleaner around all the mating points and the throttle shafts while running, if no leaks are found, try setting and syncing the carbs again.

If it was injected there would be a P shaped boss on the head between the valve cover and the manifold inline with each intake runner.

PCV check- Pull the pcv and brake booster (if it has a booster) hoses off the intake, and plug the intake them. See if that changes anything.
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Old 04-29-2021, 06:35 PM   #8
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^ Agreed. I tried a few gaskets on a stubborn B20 of mine with the same symptoms before I realized the manifold was warping slightly only after it warmed up. The gaskets were just not thick enough to make up for it.
I finally solved the problem by using gasket sealer. This is not something I'd normally recommend, but I was too broke to have the manifold resurfaced at the time.
It fixed the problem.

OP - What carbs to you have and do the butterflies have the little spring / override valve?
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Old 04-29-2021, 06:47 PM   #9
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Quote:
Originally Posted by 1968 volvo View Post
Whats the best way to post a photo on here?
Imgur is the site where most people host their pics.

If you donate to TB you can upload pics to the server after your name turns blue.

https://forums.turbobricks.com/showthread.php?t=356726
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Old 04-29-2021, 06:56 PM   #10
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Originally Posted by hiperfauto View Post
Imgur is the site where most people host their pics.

If you donate to TB you can upload pics to the server after your name turns blue.

https://forums.turbobricks.com/showthread.php?t=356726
Here is the picture of my engine bay for all to see.

https://imgur.com/a/8sLShnc
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Old 04-29-2021, 07:04 PM   #11
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^ Agreed. I tried a few gaskets on a stubborn B20 of mine with the same symptoms before I realized the manifold was warping slightly only after it warmed up. The gaskets were just not thick enough to make up for it.
I finally solved the problem by using gasket sealer. This is not something I'd normally recommend, but I was too broke to have the manifold resurfaced at the time.
It fixed the problem.

OP - What carbs to you have and do the butterflies have the little spring / override valve?
I believe the carbs i have are the su-hs6? There is a second set of butterfly valves in the intake manifold if thats what you mean.

As for Gasket sealer that may be the best option if the gaskets are leaking... I understand its not the best option but I am on quite a restrictive budget. Is it also possible to get a thicker gasket to make up for any potential imperfections?
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Old 04-29-2021, 07:22 PM   #12
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That's not what I meant, but that second set of butterflies can also be a source of leaks.
The things I was talking about are on the carb. butterflies. You'd know them if you saw them.

I do not know of a thicker gasket. I once tried to fix it by using two gaskets, but that made no difference.
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Old 04-29-2021, 07:24 PM   #13
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Quote:
Originally Posted by 1968 volvo View Post
I believe the carbs i have are the su-hs6? There is a second set of butterfly valves in the intake manifold if thats what you mean.

As for Gasket sealer that may be the best option if the gaskets are leaking... I understand its not the best option but I am on quite a restrictive budget. Is it also possible to get a thicker gasket to make up for any potential imperfections?
Your PCV setup looks OK to me. I would go through and check all the hoses for cracks. Do the carb cleaner trick to check the gaskets.

I've read about the dual butterfly setup causing issues. Maybe those throttle shafts are worn? The preferred setup for a B18/20 and dual SUs seems to be a cast dual port exhaust manifold and aluminum intake manifold or the one piece setup without the secondary butterflies.

The valve alshnertz is talking about is a little disc and spring on the throttle plate inside the carburetor. The later HS6 and HIF6 carburetors got them and sometimes cause problems.
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Old 04-29-2021, 08:03 PM   #14
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Yeah, the PCV/booster hoses appear to be connected properly but it's difficult to tell from the pic how they're attached at the manifold.

It looks like you're still using a PCV valve from the B18. B20's used a restricted fitting on the manifold instead. It's a cleaner setup and doesn't rattle like a PCV valve. They're available new but they're pricey.

https://vp-autoparts.com/en/artiklar...0_b30-2mm.html

The intake manifold with the extra butterfly valves has a couple of other places that can introduce a vacuum leak. The plate between the carbs has a gasket that can leak and there are plugs in the manifold for the secondary butterfly shafts on the inboard side that may have fallen out or been accidentally knocked out. Also, there should be a vacuum seal on the outside of the manifold on the secondary butterly shafts.

I like to remove the secondary butterflys completely and I keep the plugs in stock.

I think the most likely cause of your high idle is that the linkage between the carbs got flipped over during the carb service and now the linkage isn't pulling the throttles closed.
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Old 04-29-2021, 10:51 PM   #15
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Originally Posted by alschnertz View Post
That's not what I meant, but that second set of butterflies can also be a source of leaks.
The things I was talking about are on the carb. butterflies. You'd know them if you saw them.

I do not know of a thicker gasket. I once tried to fix it by using two gaskets, but that made no difference.
The butterfly valves appear to be solid pieces of brass.
Here are two shots of them.

https://imgur.com/a/6WNE26g

Maybe just gasket sealer is the safest approach
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Old 04-29-2021, 11:09 PM   #16
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Yeah, the PCV/booster hoses appear to be connected properly but it's difficult to tell from the pic how they're attached at the manifold.

It looks like you're still using a PCV valve from the B18. B20's used a restricted fitting on the manifold instead. It's a cleaner setup and doesn't rattle like a PCV valve. They're available new but they're pricey.

https://vp-autoparts.com/en/artiklar...0_b30-2mm.html

The intake manifold with the extra butterfly valves has a couple of other places that can introduce a vacuum leak. The plate between the carbs has a gasket that can leak and there are plugs in the manifold for the secondary butterfly shafts on the inboard side that may have fallen out or been accidentally knocked out. Also, there should be a vacuum seal on the outside of the manifold on the secondary butterly shafts.

I like to remove the secondary butterflys completely and I keep the plugs in stock.

I think the most likely cause of your high idle is that the linkage between the carbs got flipped over during the carb service and now the linkage isn't pulling the throttles closed.
Does the pcv valve screw into the manifold?

Here's two better pictures of the intake manifold side.

https://imgur.com/a/OTRa0lN

Are the plugs to eliminate the secondary butterfly valves for sale anywhere? Im all about simpler. Thanks for the advise Ill check the linkage asap.
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Old 04-29-2021, 11:17 PM   #17
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Your PCV setup looks OK to me. I would go through and check all the hoses for cracks. Do the carb cleaner trick to check the gaskets.

I've read about the dual butterfly setup causing issues. Maybe those throttle shafts are worn? The preferred setup for a B18/20 and dual SUs seems to be a cast dual port exhaust manifold and aluminum intake manifold or the one piece setup without the secondary butterflies.

The valve alshnertz is talking about is a little disc and spring on the throttle plate inside the carburetor. The later HS6 and HIF6 carburetors got them and sometimes cause problems.
The vacuum hoses were replaced 2 weeks ago. is it possible that they cracked already? I assume its good to double check.

Ill investigate the second butterfly valves being bad.

Whats a good place to shop around for intake manifolds?
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Old 04-29-2021, 11:55 PM   #18
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Originally Posted by 1968 volvo View Post
Does the pcv valve screw into the manifold?

Here's two better pictures of the intake manifold side.

https://imgur.com/a/OTRa0lN

Are the plugs to eliminate the secondary butterfly valves for sale anywhere? Im all about simpler. Thanks for the advise Ill check the linkage asap.
Yes, the PCV fitting screws into the manifold. There is no valve per se. The fitting just has a small hole that draws the crankcase vapors into the intake all the time.

It appears that you have an intake manifold from a '68 122 that only has one place for a fitting. You need 2 to use the B20 PCV fitting on a 140 because you need manifold vacuum for the booster. You would need to tee off the one vacuum source to use the B20 PCV fitting.

I have the plugs to eliminate the secondary butterfly valves listed on my web site but it's best to contact me through PM if you want them.

http://hiperformanceautoservice.com/...oducts_id=1519
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Old 04-29-2021, 11:55 PM   #19
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Quote:
Originally Posted by alschnertz View Post
My guess is that your intake manifold is slightly warped and after the car warms up, the seal between it and its gasket no longer seals and extra air in induced into the head.

You can try spraying carb cleaner around the manifold when it's idling high. If the idle goes down, you have a leak.
This does not work 100% of the time though because it's hard to reach all the areas.

Check that the intake mating surface is "true".
1968 volvo
Cannot see your response to this - have you tried that yet?
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Old 04-30-2021, 12:14 AM   #20
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Cannot see your response to this - have you tried that yet?
I haven't tried it yet Ill let you know soon as I do.
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Old 04-30-2021, 04:38 AM   #21
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I just did a job with the same issues, customer just had the carbs rebuilt by a"shop". the throttle plates were worn, no matter how much you backed off the idle screw. Air leaked around the sides. New plates solved the problem
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Old 04-30-2021, 10:30 AM   #22
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I just did a job with the same issues, customer just had the carbs rebuilt by a"shop". the throttle plates were worn, no matter how much you backed off the idle screw. Air leaked around the sides. New plates solved the problem
OP got his carbs rebuilt with Delrin bushings, there is only one guy I know of who does that, Tom Bryant. When he did my HS6 bodies they got new throttle shafts and plates. So I would guess OP got the same?
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Old 04-30-2021, 11:08 AM   #23
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OP got his carbs rebuilt with Delrin bushings, there is only one guy I know of who does that, Tom Bryant. When he did my HS6 bodies they got new throttle shafts and plates. So I would guess OP got the same?
Tom Bryant is the guy who I hired. Its possible that the throttle plates aren't new. But I'm confident that he would have fixed them if they were bad.
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Old 04-30-2021, 08:38 PM   #24
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Hello. I tried doing the carb cleaner on my car... nothing showed up until the car was warm. Once it warmed up, I was able to find it. It is for sure the secondary butterfly valves in the intake manifold. I will record it maybe tomorrow and post a video via Imgur.

What are your suggestions on how to fix it?
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Old 04-30-2021, 11:04 PM   #25
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Remove the secondary butterflies and the secondary throttle shafts and plug the holes in the manifold.

We've seen people unnecessarily drill, tap and install threaded plugs, while we have the correct size plugs that just need to be tapped in with a hammer.

If you look carefully you will see that Volvo did the exact same thing by using a tap in plug for the inner holes for each of the secondary throttle shafts.

In fact we used to re-purpose the used plugs from cracked manifolds and when that supply ran dry we bought them right from Volvo back when they were available and when that well ran dry, we sourced some from a supplier that made the right size plug.

FYI, you will need to remove the carbs to remove the secondary butterflies and if not already done, you should solder closed the decel valves that are built into the butterflies in the carburetors.

We also have carb base gaskets as they might tear when you remove the carbs.
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