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Carb woes. Any advice?
Date: August 01, 2018 05:39AM

Guys, continuing my fuel woes. Ever sense my carb shop rebuilt my carbs, Ive been having a problem. The first problem was one carb leaking, and loading up to the point that raw fuel was dumping out of my exhaust. Shop blamed it on fuel pressure but I knew it wasnt. I tested pressure anyway and it turned out, one of the floats was taking on fuel. I assume if they missed that, they could miss other things. After that, the main issue has been a dead spot under hard acceleration which occurs seemingly out of nowhere. Its not a major issue drive-ability wise so I've been ignoring it. However, since my e-fuel pump died and I went back to mechanical, I get pinging and what feels like fuel starvation at higher rpm. Whats more, I have spoken to a friend who used the same place for his quadrajet, and he is experiencing almost the same thing. Premature fuel pump failure, and starvation at higher rpm. So now Im doubting these carbs completely. They look pretty, but that’s about it. I'm wondering if the floats are set too low, and the electric pump was overcoming that, where the mechanical one cant. Or, is there a deeper issue. I don’t know carbs super well. I grew up working on fuel injection. I know enough to clean and rebuild a motorcycle carb(s), but not enough to diagnose an automobile carb issue. I think its no coincidence that me and my buddy are both having issues on two completely different engines, but carbs from the same shop. I guess first thing to do will be check float height? Btw, tank, lines, filters and pump are new and have been since carb install.

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Re: Carb woes. Any advice?
Posted by: BobV66Vair ()
Date: August 01, 2018 06:52AM

buy Bob Helts book for your cabs and rebuild them yourself. If you have his book, you can do as good a job as any shop, or better. When you take it apart, see where every linkage and piece goes. Find them in the book as you disassemble and it will make it easier to assemble. Carb kits are available from Clark's and some flaps.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Carb woes. Any advice?
Posted by: JimBrandberg ()
Date: August 01, 2018 06:57AM

If I'm having trouble and suspect the fuel level I like to remove the carb to the bench, remove the top and see what the level is. I think it should be close to but perhaps a little lower than the "ramp" going up the on end of the bowl with the main jet.
Before doing this I like to run the engine and then shut it off and then immediately loosen one of the lines to remove the fuel pressure, letting the fuel run onto a towel. It may be folly but I don't want the carb to possibly continue filling with the residual pressure.
Each time you do this it may just be a snapshot, I wonder if the level in the bowl lowers and rises a bit when the engine is running.

It does sound like perhaps you have fuel starvation under hard acceleration or high RPMs. Of course you would want to investigate when it's actually having trouble but it's difficult to just pull over out on the road and start removing the carburetors. You could cut the engine, pull over and check for an accelerator pump squirt.

So what did you have for fuel pressures with the mechanical and electric pumps?
In these days of excessive pressure with mechanical pumps it's hard to keep in mind that fuel starvation is another possible problem. Sometimes the rubber hose near the starter can suck air which hinders the mechanical pump's ability to draw fuel. An electric pump mounted by the tank is just pushing on through at this point.

I see some carburetors that are painted up nice with new hardware but have operational issues. I'm not much for paint on carburetors especially if it's on the bowl gasket surface making removing the gasket in one piece futile.
I like to put Syl-Glyde grease on the bottom of the bowl gasket so it comes off the bowl and sticks to the top.

All that fuel wash you had is tough on your cylinders and getting into the oil as well.

Just some thoughts and I'd like to read more. I certainly have my share of trouble with these carburetors.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Carb woes. Any advice?
Posted by: MattNall ()
Date: August 01, 2018 06:58AM

Please name the shop... no need to say anything else..

What was the pressure with the e-pump? What is the pressure now with the mechanical?





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 woes. Any advice?
Posted by: Frank DuVal ()
Date: August 01, 2018 08:10AM

I take the top off the carburetor while it is still bolted to the head to see fuel level.thumbs up

Frank DuVal

Fredericksburg, VA

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Re: Carb woes. Any advice?
Date: August 01, 2018 08:17AM

MattNall Wrote:
-------------------------------------------------------
> Please name the shop... no need to say anything
> else..
>
> What was the pressure with the e-pump? What is
> the pressure now with the mechanical?


Let me preface by saying that these guys did a 61 Cadillac Carb for me with 0 issues at all. I hate to drag them through the mud. Custom Rebuilt Carburetors in Middlesex NJ. [customrebuiltcarbs.com]

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Re: Carb woes. Any advice?
Date: August 01, 2018 08:18AM

Pressure with the electric pump was spot on 4psi. I have not checked pressure with the mechanical clarks pump. I suppose I have to find a good way to do that.

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Re: Carb woes. Any advice?
Posted by: MattNall ()
Date: August 01, 2018 08:21AM

No Mud! Everyone makes mistakes some time!! We just need to see if it the same as named before...





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 woes. Any advice?
Date: August 01, 2018 08:22AM

They had some sort of bronze coating on them, not paint. It doesn’t wash off with gasoline. They are clean inside and out, or rather were when I checked the leaking float.

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Re: Carb woes. Any advice?
Posted by: DAVECS1 ()
Date: August 01, 2018 09:56AM

I assume they have been properly balance when installed, using a carb sync tool. And that all vacuum leaks have been accounted for. Carb is no different then EFI the levers are justin different places.

THe carb sync tool should give you a good idea on the signal the carb is getting (aka how much air is venturing down the carb to suck the fuel into the engine) So if that looks good then I would get a vacuum gauge on it while it is running. Make sure the ottal vacuum is sufficient to work with the stock jetting in the carb. As the engines get older sometimes the vacuum signal gets a bit weaker and a bigger jet can crutch it. All this is equal to tuning the VE table in EFI. You have a MAP sensor that senses vacuum and the injectors squirt the corresponding amount of fuel.

I assume it is idling fine, but I have also found if you are having low load driveability issues the carb can go back and forth off the idle circuit and if it is not ride low engine speed driveability is not good. This is similar to how you Inlet air stepper motor regulates the air with the throttle closed so it better matches min duty cycle of your injectors and creates a steady idle or cruise.

Then there is accelerator pump. Easy check. Look down the carb, if it squirts when you hammer the throttle it is working. If the car stumbles it is still working it just may be too much or not enough, and then you get to play with springs and linkage arms. On EFI this is similar to tuning the power enrichment circuit.

FUel supply is a bit of a tricky issue I suppose. If your flooding then of course the float is not shutting the fuel off and it is pouring down the carb. Other than that if the float can shut then you just need to have a enough fuel you cannot outrun the bowl and suck it dry. THe bowl should be good for a about 5 or 6 pump shots and then steady state accelerations.

1964 Monza Convertible
110 4 speed
Peoria, IL

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Re: Carb woes. Any advice?
Date: August 01, 2018 01:52PM

DAVECS1 Wrote:
-------------------------------------------------------
> I assume they have been properly balance when
> installed, using a carb sync tool. And that all
> vacuum leaks have been accounted for. Carb is no
> different then EFI the levers are justin different
> places.
>
> THe carb sync tool should give you a good idea on
> the signal the carb is getting (aka how much air
> is venturing down the carb to suck the fuel into
> the engine) So if that looks good then I would get
> a vacuum gauge on it while it is running. Make
> sure the ottal vacuum is sufficient to work with
> the stock jetting in the carb. As the engines get
> older sometimes the vacuum signal gets a bit
> weaker and a bigger jet can crutch it. All this is
> equal to tuning the VE table in EFI. You have a
> MAP sensor that senses vacuum and the injectors
> squirt the corresponding amount of fuel.
>
> I assume it is idling fine, but I have also found
> if you are having low load driveability issues the
> carb can go back and forth off the idle circuit
> and if it is not ride low engine speed
> driveability is not good. This is similar to how
> you Inlet air stepper motor regulates the air with
> the throttle closed so it better matches min duty
> cycle of your injectors and creates a steady idle
> or cruise.
>
> Then there is accelerator pump. Easy check. Look
> down the carb, if it squirts when you hammer the
> throttle it is working. If the car stumbles it is
> still working it just may be too much or not
> enough, and then you get to play with springs and
> linkage arms. On EFI this is similar to tuning the
> power enrichment circuit.
>
> FUel supply is a bit of a tricky issue I suppose.
> If your flooding then of course the float is not
> shutting the fuel off and it is pouring down the
> carb. Other than that if the float can shut then
> you just need to have a enough fuel you cannot
> outrun the bowl and suck it dry. THe bowl should
> be good for a about 5 or 6 pump shots and then
> steady state accelerations.
Idle is smooth and low rpm even under a heavy load is smooth and about as powerful as 80hp can be. Its literally just an issue when you’re in passing conditions. Cruising speed I hear some pinging even with timing being spot on and 93 octane, although I usually run regular.

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Re: Carb woes. Any advice?
Date: August 01, 2018 02:08PM

It almost feels like the accelerator pump doesn’t have enough throw. Like it runs out of spray halfway through. You might be on to something with manipulating the linkage, but visually it seems to work fine.

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Re: Carb woes. Any advice?
Posted by: MattNall ()
Date: August 01, 2018 02:43PM

Take the bent rod off... actuate the pump manually and you'll see how to adjust..

Sometimes I've shortened the arm up to 3/8" and drilled a new hole in it.





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 woes. Any advice?
Posted by: DAVECS1 ()
Date: August 01, 2018 07:03PM

MattNall Wrote:
-------------------------------------------------------
> Take the bent rod off... actuate the pump manually
> and you'll see how to adjust..
>
> Sometimes I've shortened the arm up to 3/8" and
> drilled a new hole in it.


I had to do this on my carbs when I had them. Ran great afterwards.

1964 Monza Convertible
110 4 speed
Peoria, IL

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Re: Carb woes. Any advice?
Date: August 03, 2018 05:09AM

Ok, thanks. I will take the air cleaners off tonight and see what I get.

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Re: Carb woes. Any advice?
Date: August 04, 2018 01:49PM

Finally had a moment to work on my own vehicle and guess what.. Crap. Before starting the car, I yanked the filters and pumped the linkage. No fuel. I know there is fuel in the carbs from when I parked it, but hell lets make sure. Started her up (just a quick crank) and let it idle for a minute. Cut the ignition and pumped the linkage. Nothing. Pulled the accelerator pump rod off and there is about an inch of free play and then some sort of resistance pumping feeling. Still no fuel spray though. Are you telling me that this @#$%& goddamned thing has been relying on engine vacuum alone to pull fuel for over a year? Christ all mighty, I'm about to go launch these carbs through that shops window.

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Re: Carb woes. Any advice?
Posted by: steve c goodman ()
Date: August 04, 2018 02:14PM

Over a year since it has run? Don't blame the carbs. Our cars need steady exercise.

The shelf life of new fuels is minimal. The new fuels have a bad effect on rubber, it hardens pieces such as accel pump cups and diaphrams and rubber fuel lines.

best wishes, Steve
Rear Engine Spec. Inc. Golden, Colo.

1962 spyder 3.0L turbo---1965 Crown V8
1967 monza 110/4---1968 monza 110/4
1971 amante gt 110/4
CORSA/RMC/PPCC

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Re: Carb woes. Any advice?
Date: August 04, 2018 02:32PM

No No, i drive it daily. Read my first post. The carbs were done by a local carb shop about a year ago and Ive had problems since.

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Re: Carb woes. Any advice?
Date: August 05, 2018 05:57AM



There you have it.

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Re: Carb woes. Any advice?
Posted by: Lane66m ()
Date: August 05, 2018 06:11AM

Get the Viton accelerator pump cups from California Corvairs, JASVAIR (on Forum) or Rafee (corvair1 on web). Install them and put carbs back together with new gasket. Set them up again and see how it runs.

You might want to clean out the carb with carb cleaner just to make sure all passages are clear while it is apart.

Al Lane
Ellabell GA

1966 Monza Coupe, 110 hp, 4 Spd
1968 Camaro SS Coupe 350 CI 295+ HP PG
1964 Greenbrier Deluxe, 6 dr, 80 hp car engine, PG
2015 Chevrolet Malibu 2LT
2018 Chevrolet Silverado LTZ Z71 Centennial Edition
1947 Farmall A tractor 15 hp





Edited 1 time(s). Last edit at 08/05/2018 06:12AM by Lane66m.

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