Are these holes in carb intended to have screws in them?

304065 · 06-18-2011, 01:58 PM

Well I put the carbs on today, Weber 40IDA3C.

I put M5 nylocks on the pointed studs to hold the velocity stacks.

Now I notice some threaded holes in the carb tops
Identified in this photo.

Do these need screws in them? What locking method if yes, so they don't back out and fall down the jet holes? Or do you leave them open? I don't remember if there were any screws in them on disassembly (five years ago).

Thanks!

304065 · 06-18-2011, 06:35 PM

never mind . . .

ratpiper71T · 06-20-2011, 05:18 AM

Just ou of curiosity-I didn't see in you other threads- did you do or have done the float well baffle and anti percolation mods?

304065 · 06-20-2011, 07:15 AM

Yep, Bieker did all that.

Carburatori Bellissimo! Restored Weber IDA3C

Walt Fricke · 06-20-2011, 11:47 PM

I once made the mistake of holding the velocity stacks on with machine screws. Sure enough, some got loose, and fell into the throats. Only one of the three affected pistons was a writeoff, but not pretty or helpful. I could hear something was wrong as my wife drove the last couple of laps of an enduro.

Do you actually have those screen covers? I've never had any. Instead, I have put a piece of open cell foam into the recess they cover, which is then under the aftermarket air filter base (which has holes in the right places). Seems to do the trick of keeping sand grains and the like out of the innards. But the stock pieces would probably be better.

304065 · 06-21-2011, 05:10 AM

Walt, I don't have those screens, they are a performance mod for folks running mesh-type filters. I realized what the threaded holes were actually for when I found that photo.

Nice, no? Of course one would have to shorten the float vent tubes.

Walt Fricke · 06-21-2011, 12:11 PM

Ah - float vent tubes. My 46s don't have them.

I'm trying to recall the setup on the 40s I ran on a 2.3 motor, but I sold them a ways back and can't recall if they had those tubes or not.

But one should do something to prevent debris from finding its way into the air corrector etc. stack. With the float stacks sticking up, what serves this purpose?

304065 · 06-21-2011, 03:48 PM

Quote:

Originally Posted by Walt Fricke

Ah - float vent tubes. My 46s don't have them.

I'm trying to recall the setup on the 40s I ran on a 2.3 motor, but I sold them a ways back and can't recall if they had those tubes or not.

But one should do something to prevent debris from finding its way into the air corrector etc. stack. With the float stacks sticking up, what serves this purpose?

Walt,

The factory intended that these be contained inside the airbox. The bathtub shaped housing is secured to the top of the carb by the studs that hold the velocity stacks down, and everything inside receives filtered air.

Which is a concern, particularly for SWB owners, where rust finds it way into the air filter housing. Eventually rust flakes end up in the float bowls, clogging things, or in the jets, clogging them further. Most guys don't take the time to detail the INSIDE of their air cleaner housing, but that's a very important step to prevent these issues down the line. It also makes it easier to wipe the oil film blowby out at every oil change.

1QuickS · 08-22-2011, 08:36 PM

The pretty picture of the Weber top cover with the air horns is one I took to showcase those little screens I make and sell to the racers. The screens cover the emulsion tube wells and were for use when open intakes were used for race applications; since road debris has direct access into the fuel bowls and down the air corrector/emulsion tube stack it can quickly find its way to the idle jets and plug them first: they have the smallest orifices in the Webers except for the squirter nozzles.

Rust can develop in the vent pipes which drops directly into the fuel bowls. When I remanufacture a set of Webers I remove and replate these. Also, these OEM boats have rubber seals that set into a trough, this trough can collect water and rust. This rust is then drawn into the air cleaner (bypassing the filter) and directly into the fuel wells; I learned about this a long time ago after having #3 idle jet blocked with rust flakes on a frequent basis.

OEM and K&N types of air cleaner housings make use of the four M4 tapped screw holes to assure a complete seal around the emulsion tube well; wave washers are the locking device used.

304065 · 08-25-2011, 03:43 AM

Paul, are you saying that there should be M4 screws in those holes when the factory boats and air cleaner are used?

Why do you advertise those screens for race use only?

Why did the factory have the float vent tubes stick up past the top of the carb on the 40s, but cut them off on the 46?

1QuickS · 08-25-2011, 06:33 AM

Air screens were needed when open air horns were used to keep small crud from entering the fuel well and emulsion tubes which could later block the idle jets and possibly larger chunks could block the mains.

These screens are used for racing since they are not needed when air cleaners are installed over the entire top of the carburetor. If they are used then the vent pipes in the top cover must either be drastically shortened or removed altogether.

The vent tubes on production Webers have had two different lengths; the tall ones like you mentioned and a short version as used on the IDS throttle bodies (for 2.0 S's for '67 and '68.) I think that vent pipes help keep sloshed fuel from draining down the sides of your carb; the IDS version was machined to have a reduced ID in its short body where the taller ones were constant ID through their length. The racing 46's had vent holes that were a smaller diameter than those required to install vent pipes for OEM applications which helped keep sloshed fuel loss to an acceptible minimum. Otherwise, I doubt that sloshed fuel is a concern to racers.

I recommend using the M4's to help conform the thin metal of the air cleaner "boat" to the sealing gasket on top of the carb to keep as much junk from being sucked into the carb as possible. Remember that the air cleaners are operating under vacuum or at least at a lower air pressure than ambient so dust will be drawn through any discontinuities in the seals of your air cleaner.

Walt Fricke · 08-25-2011, 01:57 PM

If I ever go back to carbs, I will purchase four of Paul's nice screens. Because I have found bits of crud inside my air filters (aftermarket pleated or foam type). I once had a fould main jet with a little piece of tar blackened sand in it. Found it with an IR heat gun - one exahust of six was distinctly cooler than the rest. Unscrew the jet, and voila - there's the problem.

My solution was a piece of open cell foam in the recess in the carb body under each opening in the "boat" plate of the air filter assembly. Kept crud from getting in. No doubt the factory oil bath cleaners were less likely to admit stuff like this. Don't know how it gets in, but it does.

Though neither my 40 nor my 46 had the tall tubes.

Walt