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Venturi cluster.
Posted by: northrop n9m ()
Date: January 30, 2020 02:59PM

Hi
I have a 66 convertible corsa 140 4spead. I'm having trouble on one of the primary cards, fuel is dribbling from the venturi cluster at idle. I've checked the float level and tried lowering and raising it, I've changed the Custer gasket and swapped the carbs side to side. What else am I missing.
Thanks. Lane.

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Re: Venturi cluster.
Posted by: joelsplace ()
Date: January 30, 2020 03:18PM

The clusters get warped so you have to remove the brass tubes and file them flat but that will not cause your problem. You probably have too much fuel pressure.

Joel
Northlake, TX
5 Ultravans, 114 Corvairs and counting...

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Re: Venturi cluster.
Posted by: MattNall ()
Date: January 30, 2020 03:35PM

As Joel suggests.. Check fuel pressure! If over 4 psi with engine idling

Electric pump... buy a 2-4 psi pump or install a regulator.

Mechanical pump Cut coil spring under top cover until pressure is in range.

Here's how to test pressure. You can buy all, including line premade.

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Re: Venturi cluster.
Posted by: dryenko ()
Date: January 30, 2020 03:38PM

Later carb kits have a needle seat hole bigger than the originals from GM.
This also can overpower the floats.
You also may have a float that is filling with fuel.
Check your fuel pressure fist.
The replacement pumps have too strong a spring.
I have seen them with over 10lbs fuel pressure.
4-5 psi is plenty.
Your opinion may vary [YOMV ]

Bob C aka Dryenko
Dobson, NC 27017

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Re: Venturi cluster.
Posted by: northrop n9m ()
Date: January 30, 2020 05:11PM

Hi
Thanks for the information. I forgot to mention I have replaced the fuel tank, fuel lines and installed a California corvair low pressure electric fuel pump. Maybe the neatle and seat are bad.
Lane

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Re: Venturi cluster.
Posted by: MattNall ()
Date: January 30, 2020 05:21PM

The Drip followed the car? check the carb... and if nothing shows... lower the float level 1/8"

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: Venturi cluster.
Posted by: JimBrandberg ()
Date: January 30, 2020 06:39PM

There was a thread on here a few years ago about sanding the venturi cluster gasket surface flat. I made a tool from a needle nose pliers for removing the brass tubes after reading that thread. There's a picture of his tool for that and some pictures of the progress being made when sanding it on a flat surface. I use emery paper on my 3/8 steel plate bench top.

Yes too much fuel pressure is the number one offendor.

I get smaller needle and seats from Grant Young at Wolf Industies.
I haven't check lately but the ones from Clarks a few years ago were even bigger than original LM. I don't know the hole sizes off the top of my head.

I have MUCH frustration sometimes getting them to stop dripping. Sometimes it seems to be a factor of the side to side synchronization.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Venturi cluster.
Posted by: v8vair ()
Date: January 31, 2020 06:01AM

Ive seen this a few times. Both times the needle Base wasn't tight and the fuel was leaking by the gasket. Almost drove me insane smiling smiley Mike

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine



Edited 1 time(s). Last edit at 01/31/2020 06:07AM by v8vair.

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Re: Venturi cluster.
Posted by: cnicol ()
Date: January 31, 2020 06:29AM

Another possibility: Idling on the main jet due to a plugged idle jet. Idle speed screw gets cranked-in until there's enough airflow to get the cluster to drip. Is your idle speed screw adjusted abnormally far down?

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Venturi cluster.
Posted by: northrop n9m ()
Date: January 31, 2020 07:13AM

Thanks for all the input. I'm going to pull the carb back off on sat, I will change the needle and seat make sure the cluster base is flat, make sure the idle jet is clean and start from scratch with the carb adjustment's.
thanks again for all the information.

Lane

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Re: Venturi cluster.
Posted by: cnicol ()
Date: January 31, 2020 11:16AM

In my experience, warped clusters are reluctant to flow fuel and cause large hesitation. I think the "warped, (leaking gasket) cluster theory is a red herring when the issue is flowing too easily or overfull fuel bowl. JMO

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: Venturi cluster.
Posted by: corventure Dave ()
Date: January 31, 2020 11:46AM

Craig is right. A warped cluster will not likely be a venture drip issue. The warped cluster will interrupt the vacuum flow.

Also check the float spring. It not only helps with float bounce, it also helps maintain float level. I adjust mine so the float assembly is almost weightless against the needle valve. Fuel pressure will assure the valve will open completely. So tightening up the float spring a little will not effect fuel delivery, but will assist the float to keep the needle valve from flowing all the time. This works especially when lowering the float level does not solve the venture drip issues.

Corventure Dave

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Re: Venturi cluster.
Posted by: Brizo ()
Date: January 31, 2020 11:51AM

I've also seen float springs install several incorrect ways that could restrict free float movement .

Dan Brizendine, Circle City Corvairs
'64 8door Greenbrier 140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"

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Re: Venturi cluster.
Posted by: v8vair ()
Date: January 31, 2020 12:47PM

I thought the seat was tight but it hadn't crushed the gasket. These were from previous rebuilt carbs and I believe the bead blast process marred the threads so it took a lot more to tighten them. Mike

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

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Re: Venturi cluster.
Posted by: joelsplace ()
Date: January 31, 2020 01:54PM

I mentioned the warped cluster as a don't forget to check while you have it apart item.
Sorry for the confusion. I should have been more clear.
It certainly won't cause dripping.

Joel
Northlake, TX
5 Ultravans, 114 Corvairs and counting...

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Re: Venturi cluster.
Posted by: JimBrandberg ()
Date: February 01, 2020 07:44AM

I' m reluctant to disagree with Craig but sanding the cluster gasket surface flat has stopped the dripping for me sometimes.
Some have reported a "bacon frying crackling" sort of a noise associated with it but it's subtle.

One clue that you've cranked the idle stop screw down beyond the idle circuit is that the throttle plate edge no longer covers the vacuum advance. When idling properly you should be able to hook up the VA hose and see no change.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Venturi cluster.
Posted by: joelsplace ()
Date: February 01, 2020 08:18AM

How could that work Jim? The cluster uses vacuum to pull fuel through it. If it leaks there is less vacuum available to pull fuel.
At closed throttle there isn't any vacuum there anyway so high fuel level is all that can make fuel flow through the cluster.

Joel
Northlake, TX
5 Ultravans, 114 Corvairs and counting...

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Re: Venturi cluster.
Posted by: JimBrandberg ()
Date: February 01, 2020 01:06PM

I can't say how it works only that it has for me on occasion.
Perhaps the other thread I referenced from a few years ago has more information.

Jim Brandberg
Isanti, MN
CorvairRepair.com



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Re: Venturi cluster.
Posted by: v8vair ()
Date: February 01, 2020 02:11PM

Im no engineer. so what I say may be wrong. Atmospheric pressure is what pushes the fuel through the main jet, then through the atomizer tube then through the bottom of the cluster. What we refer to as vacume is actually lower atomospheric pressure from the piston going down and the butterfly opening. So the way I see it the fuel is pushed through the cluster ??? Once the Pressure drops in the Venturi the atmospheric pressure of 15 or so in the float bowl is more than in the venturi. The rush of air coming by the cluster helps atomize the fuel in the venturi. Ok now that I confused myself ill stopsmiling smiley Mike

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

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Re: Venturi cluster.
Posted by: joelsplace ()
Date: February 01, 2020 05:24PM

Yes that is correct. Fuel technically isn't pulled through the venturi.
Sometimes it helps to know what is really going on instead of what it looks like.

Joel
Northlake, TX
5 Ultravans, 114 Corvairs and counting...

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