Venturi's in action in idle

[Marx3]

Hi first post ever!

I have recently rebuild a 7043202 carb, though I usually buy Hygrade's kits ( actually rebuild several Qjets ), this time I bought a cheaper one from Echlin.
It is supposed to service a handful of carbs with different cast-numbers.

The problem is that in idle, the engine sucks fuel out of the venturi's. It is not dripping, the fuel is flowing out of them. very weird.
the carb has holes drilled in the plates, but still I have to open up the plates alot to get it too idle.
Tried the carb on a Buick Nailhead, and at 600 rpm it the venturi's where flowing fuel.

I am 99 % sure that I selected the right airhorn gasket and gasket for the baseplate. ( there was 3 different in the kit ) 

What am I overlooking here? or do I simply just try another gasket?

Regards Jacob

[Marx3]

forgot to mention that, though floatlevel was set to specs, I tried lowering it a bit.
I also tried blinding the holes in the plates.
No effect. Venturis still distributing fuel in idle

[Cliff Ruggles]

Do you have one of our books yet?  It covers complete/correct rebuilding, and custom tuning, etc.

That carburetor has an idle bypass air system, which is more effective than drilling the throttle plates to lower the angle at idle speed.

I would imagine the idle tubes are plugged up some, or not large enough for the application.

Viton parts are manditory these days.  We sell Viton high flow needle/seat assemblies and complete accellerator pump assemblies.  Aftermarket kits will not contain the correct components as the supplier of parts for these kits is still using up old stock.....Cliff

[Marx3]

I have just bought your book, it is on it's way across the sea!

I have rebuild 10-15 Qjets in the past, and have never seen this before, but on the other hand, have never used Echlins cheap kits.
I will try cleaning it out again!
Can you explain to me exactly what is happening that makes the fuel flow form the venturies?

And if that does not work, I will buy a Hygrade kit, they come pretty cheap here in Europe. I ain't quite ready to spend 80 bugs and have it flown overseas, tax etc. just yet. Not on this carb at least. I dont mean to sound cheap, I think I will use your kits in the future!
thanks for the reply!
Regards Jacob

[Cliff Ruggles]

Unfortunately, you will find that all of the currently available over the counter kits will not contain good parts.  All of the companies who made and sold carburetor kits have went out of business, or have been bought out by one major company.

We buy carburetor kits from various sources periodically to check out the contents.  They will NOT contain Viton parts in most cases, and not even the correct parts.  They will also not contain a lot of parts that we consider manditory items to replace during rebuilding, such as the secondary plastic cam/spring, Viton high flow needle/seat assemblies, power piston spring, upgraded accellerator pump with new springs, etc.

Are incomplete kits with inferior parts in them really a bargain?.....Cliff

[Marx3]

Inferior kits are no doubt about it, not worth the effort installing! But now I know your site, right

btw, would you explain the physics of the venturies flowing fuel, I cant get it into my head.  Is it the lack of available air from the bypass system that creates a stronger signal in the boosters?

[77cruiser]

With too much airflow through the venturis they're going to pull fuel. Does the carb have an idle bypass?
Can you increase your timing to bring the idle up & then close the throttle a bit?

[Marx3]

Obviously is airflow sucking the fuel out of the venturi's But why!!! Is it solely because of some fault in the idlebypass system, or can it also be due to a wrong gasket?

I dont see the typical bypass system on the backside of the carb. Just the unused area and two unthreaded holes where the screws would be. Man I am confused on this one.

[Marx3]

Forgot to mention that on a Nailhead 425 idling at 600 rpm, 16-17 Hg, and about 35 degrees of advance ( with manifold vacuum ) they still distributed fuel... really weird.

[Cliff Ruggles]

Did you pull the idle tubes during the rebuild to make sure they were not blocked or obstructed?  In most cases they will have considerable debri, dirt, corrosion in and under them. 

When placed in service with insufficient idle fuel, the idle speed screw will need to be turned in to sustain the engine, it pulls fuel from the boosters (nozzle drip).....Cliff

[Marx3]

I did not pull them, but i made sure I could blow air through them. I will re-check them and make sure! I must admit that I also tried the carb on a SBC and started it up real quick without a fuel filter. Foolish of me, should have known better. It flooded instantly, so theoretically there could be some new dirt in the tubes. I will check up and report back!

[Marx3]

Hmm, turned out it was dirt in the left idletube. or down restriction. Non the less, poking a thin piece of wire through them helped open up the effect on the left mixturescrews and Wham! The Nailhead came to proper life!
Just recieved your book Cliff. Officially my new bible. Thanks!

[Cliff Ruggles]

We pull the idle tubes on any level of carb build here, always have.  Most shops simply "rod" them out, but there will often be considerable dirt/debri under them, since the area below them is not accessable.  Sooner or later they will get plugged up, seen this happen way too many times. 

Our HP kits come with new idle tubes, so have no fear if you mess them up some pulling them out.....Cliff

[Marx3]

How do you pull them up? or is that an industrial secret ;-)

So when I order my kit for the next rebuild, you can determine which tubes I need based on the carb-number?
btw, when I need a kit, where do I go? Do I fill out the form on the homepage?

[Cliff Ruggles]

We can pre-drill the idle tubes if requested.

The information to pull them is in the book.

Contact us directly for parts, cliffshp@embarqmail.com, 740-397-2921...thanks...Cliff