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Carb sync. No vacuum right side.
Posted by: smokejumper98 ()
Date: November 05, 2020 02:04PM

Here are the stats:
1963 Monza Spyder that had previously been converted to a 1961 motor with PG. (I have the original Turbo motor that I would eventually like to rebuild but I don't have a 4 speed manual.)

I have been trying to get the carbs sync'd up but it is kicking my a**. The left side carb has plenty of vacuum, but the right carb has virtually no vacuum below 1200 rpm. Here is what I have done so far:

Compression test:
1-120 2-125
3-130 4-120
5-110 6-110

Search for vacuum leak. Non detected. Sprayed carb cleaner all around base and carb. Sprayed the balance tube (even tested everything with the balance tube unhooked and capped off.)

Adjusted the valves while running. 1/2 to 3/4 turn past clacking noise.

Checked dwell, looks good at 31.
Set timing to 14.


I have used the manual and gone through all the steps for linkage adjustment and setting the fast idle over and over again.

Here is what I have to do to sync the carbs. Once I have the linkage set as described in the manual and numerous other threads here, I have to adjust the throttle rod linkage on the left carb down in the swivel to raise the idle on the right carb to almost 1800 rmp to get a similar vacuum reading on both carbs. When they are sync'd at this high of rpm there is not enough adjustment on the curb idle screw to bring the carbs down to a reasonable level idle. I am sure I am probably doing something wrong but I don't know what.

Buena Suerte, Todd
Boise, ID
1963 Monza Spyder

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Re: Carb sync. No vacuum right side.
Posted by: TerribleTed ()
Date: November 05, 2020 02:13PM

Sounds like you have a carb with a blocked idle circuit. all the things you did are nice but probably not related to the issue. If the carb is not closed off (idle speed set so low that the throttle plate is closed) then the idle circuit is not working. With the engine idling block the R carb with your hand. Does the engine slow down and stumble or change little? Do the same with the L carb. What does it do here kill the engine? I bet covering the good carb will kill the engine and the R when covered will not change much. A bit of trash in the fuel has maybe blocked the idle passage.

Sometimes this can be unblocked by accelerating the engine to 2000-4000 RPM and while holding this RPM slap your hand over the offending carb a number of times blocking and unblocking its flow. If it starts idling on the R side again you might be ok (unless it recurs). If not disassembly and thorough cleaning of the carb or carbs is the best course to take. If they have not been rebuilt recently. this is a good time to do it. If there is debris in the carbs fix the fuel system, usually caused by an old rusty fouled fuel tank...best repair of that is to replace it.

---------------------------------------------------------------------------------------------------------

Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
[www.facebook.com]



Edited 1 time(s). Last edit at 11/05/2020 02:14PM by TerribleTed.

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Re: Carb sync. No vacuum right side.
Posted by: smokejumper98 ()
Date: November 05, 2020 02:18PM

Thanks Ted.
I will look into the idle air circuit and make sure the right carb is cleaned. I had both apart recently but will pull the right one apart again. You are correct, at idle I can cover the right carb and nothing happens. If I cover the left it dies.

Buena Suerte, Todd
Boise, ID
1963 Monza Spyder

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Re: Carb sync. No vacuum right side.
Posted by: TerribleTed ()
Date: November 05, 2020 02:31PM

smokejumper98 Wrote:
-------------------------------------------------------
> Thanks Ted.
> I will look into the idle air circuit and make sure the right carb is cleaned. I had both apart recently but will pull the right one apart again. You are correct, at idle I can cover the right carb and nothing happens. If I cover the left it dies.

They can be annoying. sometimes a little particle in the passage will pass cleaners etc. and as soon as you operate the engine it moves and blocks it againsmiling smiley I have only ever pitched 2 carb bases over the years that just refused to get clear (out of over 100 carbs work on), but, I have gone back a few times on a number of them. Try the rev it up and slap the carb closed repair. I works fairly often. If it comes back down the road you can slap again or pull the carb then.

---------------------------------------------------------------------------------------------------------

Avid Corvair hobbiest since 1984.
I have personally performed ground up restoration on over 20 Corvairs.
I currently work full time at restoring and repairing Corvairs.
Located in the Atlanta Georgia area.
[www.facebook.com]



Edited 1 time(s). Last edit at 11/05/2020 02:32PM by TerribleTed.

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Re: Carb sync. No vacuum right side.
Posted by: smokejumper98 ()
Date: November 05, 2020 02:39PM

I will try that. Any suggestions on cleaning out the idle air passages if slapping the carb around doesn't work.

Buena Suerte, Todd
Boise, ID
1963 Monza Spyder

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Re: Carb sync. No vacuum right side.
Posted by: MattNall ()
Date: November 05, 2020 02:52PM

Follow Ted's advice INSIDE the carb.

OUTSIDE


1 Do you have the 1/8 insulators under both carbs? Keeps linkage from hitting head!

2 Remove both downlinks and see if problem persists.

Also, at this time you can open each carb to see how it works above idle, etc.

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
...............110-PG.................................................Webered-Turbo

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Re: Carb sync. No vacuum right side.
Posted by: smokejumper98 ()
Date: November 05, 2020 03:46PM

I do have insulators.
Problem persists with down links removed and both carbs seem to work well individually above idle.

Buena Suerte, Todd
Boise, ID
1963 Monza Spyder

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Re: Carb sync. No vacuum right side.
Posted by: jjohnsonjo ()
Date: November 05, 2020 04:02PM

If the quick steps don't work, switch the carbs from side to side. If it follows the carb, you know where to focus your inspection and rebuild.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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Re: Carb sync. No vacuum right side.
Posted by: smokejumper98 ()
Date: November 05, 2020 06:25PM

Good point JJohn

Buena Suerte, Todd
Boise, ID
1963 Monza Spyder

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Re: Carb sync. No vacuum right side.
Posted by: cnicol ()
Date: November 05, 2020 06:53PM

Here's the location of the idle jet. If you hold it up to the light just right, you should be able to see daylight through it.

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
65 Canadian Monza 4dr 110/PG 40k
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

Attachments:
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Re: Carb sync. No vacuum right side.
Posted by: Steven Barker ()
Date: August 07, 2022 12:57PM

smokejumper98 Wrote:
-------------------------------------------------------
> Good point JJohn

Hi, Any luck? Did you fix it yet I wonder? I had the same issues with my son’s 1965 Vair today.

Thanks, Steven

Vairnut1962

1957 Studebaker Silver Hawk (sold recently)
1967 Corvair coupe w/auto and factory air
1969 Corvair coupe w/4 spds and 140hp

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Re: Carb sync. No vacuum right side.
Posted by: wittsend ()
Date: August 07, 2022 03:27PM

Smokejumper98 wrote: The left side carb has plenty of vacuum, but the right carb has virtually no vacuum below 1200 rpm.

I assume you are using a tool like a Uni-Sync to determine the low vacuum reading on the one side? Regardless on any FUEL delivery problems that may or may not exist it seems like you have an AIR delivery issue to contend with - first. Either the throttle blade is completely closed off on the affected side or at the low demand for air at idle it is bleeding in elsewhere (down stream of the carburetor) and not reading on the Uni-Sync.

Others have already mentioned the carb base gaskets and the balance tube. A while back I recall there was a discussion about a rubber plug that was on a flat spring that served a purpose (air bleed???) on some of the carbs. IF your carb has those plugs and one is missing could that be an air bleed issue at idle? I don't know, I'm asking the whole group for your sake.

I have seen dual carb set ups (my experience is with Datsun and Volvo SU's) where one carb is providing all the air and fuel at idle while the other reads nothing on the Uni-Sync. Then the slightest opening of the lame carb quickly elevates the RPMs. Have you tried turning down the left side carb while turning up the right side in small increments? The lack of vacuum reading on the right side leads me to believe that you have a situation described above.

------------------------------------------------------------------------------

***'61 Lakewood, a "Freebie" in hibernation for 27 years - In the process of applying CPR.***

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Re: Carb sync. No vacuum right side.
Posted by: red monza ()
Date: August 07, 2022 04:07PM

The right side supplies vac to the vac advance...did you check to see if the vac pull off is good?

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Re: Carb sync. No vacuum right side.
Posted by: RobertC ()
Date: August 07, 2022 11:37PM

Decades ago, a piece of "metal" got stuck in the idle tube of one carb - see Craig's pic above.

Memory not great, but the symptom was engine ran poorly below 30(?) mph and ran fine above that speed.

The "valve" that wittsend mentions is on the side of the base of the carb. I believe it is for hot restart. The description / setting is in the 65 shop manual. Do not know what symptom(s) are if the spot is open all the time.



Edited 1 time(s). Last edit at 08/07/2022 11:40PM by RobertC.

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Re: Carb sync. No vacuum right side.
Posted by: Frank DuVal ()
Date: August 08, 2022 10:25AM

Quote
wittsend
Others have already mentioned the carb base gaskets and the balance tube. A while back I recall there was a discussion about a rubber plug that was on a flat spring that served a purpose (air bleed???) on some of the carbs. IF your carb has those plugs and one is missing could that be an air bleed issue at idle? I don't know, I'm asking the whole group for your sake.

The idle vent valve on the outside of the base 1964 and later carburetors can be left off and the car will run normally. It vents to top of the float bowl. When missing, it vents the top all the time, but not through the air cleaner assembly, that is all. With the valve closed, the float bowl is vented through the air cleaner assembly.

Valve added for hot start issues, not operational issues.

Frank DuVal

Fredericksburg, VA

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Re: Carb sync. No vacuum right side.
Posted by: joelsplace ()
Date: August 08, 2022 02:07PM

Frank,
We had a discussion about this a year or more ago and someone corrected me. I looked at some carburetors just the other day and the hole from the rubber disk went into the throat of the carburetor below the cluster so that would be an air leak. It may not make any I'm not saying they are all that way but the ones I looked at the other day were. I don't know what year the ones I looked at were. I really need to go through my stack and see if all of them I have are that way.

Joel
Northlake, TX
5 Ultravans, 138 Corvairs and counting...

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Re: Carb sync. No vacuum right side.
Posted by: JimBrandberg ()
Date: August 09, 2022 05:47AM

I use a Uni-Syn rather than vacuum gauge for synchronizing carburetors.
Usually before I begin I find where the throttle stop screw contacts the arm and go down 1.5 or 2 turns so they're both the same. Then adjust the left swivel to match the right one which is fixed. I generally unhook the chokes until later and make sure nothing is keeping the throttle from closing against the screw and not up on a fast idle step. When adjusting the swivel after that with the engine running it's not usually more than a turn or two.

The idle circuit goes up and through the venturi cluster and into a passage in the body of the carburetor. I spray carb cleaner and compressed air down through that hole in the body and make sure it's coming out the bottom. There's the top hole, the hole the needle goes to, the idle hole below the throttle plate and the transition slot above the throttle plate. 66 carburetors also have a hole further up from the transition slot. If you bottom out the adjuster needle it helps to force it out through the transition slot above the throttle plate. What I try to do is cover all but 1 of the holes with a finger or something and make sure the carb cleaner and compressed air will come out of the open hole.
With the transition slot and all, the idle circuit is responsible for an awful lot before the carburetor is just relying on the main jet.

P.S. I can talk a good game but I have so much trouble with carburetors it's embarrassing.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Carb sync. No vacuum right side.
Posted by: Paulsgt ()
Date: August 09, 2022 08:16AM

I had same(?) problem a couple of months back. Turns out there was something blocking the idle jet just like Craig suggests. To get good balance you will want to make sure your venturi clusters match. That is easier said than done because you have to have a way to measure the idle jet and the air bleed at the top of the cluster. Takes some very small drill bits. Bob Helt's book on carburetors is nearly a must-have if you are getting that deep into carbs. You'll want to read it 2 or 3 times.

Enjoy the Corvair!

Paul Sergeant
CORSA Central Division Director / CORSA Treasurer
Lee's Summit, MO
CORSA since 1975
Member – HACOA, Corvair Minnesota, CORSA, Little Indians, POCI


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Re: Carb sync. No vacuum right side.
Posted by: Frank DuVal ()
Date: August 09, 2022 10:11AM

Joel, the 64 and up bases have that vent tube sticking up which requires the 1/4" or so hole in the top cover gasket for that tube to stick through. 60 to 63 do not have this vent tube sticking up and can use the earlier style top cover gaskets that do not have this hole. ACDelco kits used to come with both gaskets (hole and no hole). Same with venturi cluster gaskets that in 1965 got an extra hole for the power valve. I just recently punched holes in some of my early top cover and venturi gaskets to use them on later carburetors. winking smiley This is to do those spring clean outs where carburetors need some dusting and cleaning but not rebuilding. HA!thumbs up

So, that tube sticking up is the bowl vent that leads to that side rubber vent valve. Yes, the path also does go to another place so the bowl will vent off idle.

Frank DuVal

Fredericksburg, VA

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Re: Carb sync. No vacuum right side.
Posted by: Frank DuVal ()
Date: August 09, 2022 02:32PM

More. The hole for the rubber vent valve is drilled through the "plenum" into the throttle area. This is what Joel was speaking about. This hole that enters the throttle area, just above the throttle plate when closed is about 7/64" diameter.

There are also two maybe 1/8" holes from the air cleaner area of the top cover into the top of the float bowls. Maybe this makes a "flo-through" ventilation from the air above the choke plate through the area above the fuel in the float bowls, down through the vent pipe and into the throttle plate area when the throttle is off idle and the valve closes.

Why? That 7/64" hole into the throttle area is always open to air, either straight through the valve at idle or from above the float bowls/above choke plate when off idle. So, no operational change (running) to the engine with or without the valve installed. Maybe the rubber valve is there simply to stop dirt from entering except at idle.

So, yes, air leak, but always there!thumbs up

Frank DuVal

Fredericksburg, VA

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