Weber 48 IDA small mystery

[zrayr]

What is the purpose, if any, of this cavity in the main carb body casting ? Sometimes I find there is gas in them although it seems to be completely sealed off by the cover gasket ?




Z

[Rick Parker]

In many Air cooled VW Drag Race applications the wall between the float chamber and that cavity is removed in a Vertical Mill, thus increasing the fuel volume in the float chamber.

[PaulProe]

Originally Posted by zrayr

What is the purpose, if any, of this cavity in the main carb body casting ? . . .

When making a casting, thick areas generate shrinkage problems. The casting is symmetrical about the float chamber. On one side is the hole for the accelerator pump - only one needed so nothing on the opposite side would create a large thick area. To deal with this, the designer then cored out the area to reduce the amount of metal being poured. I can understand his thinking when designing the casting to keep the float chamber symmetrical so just make this an unused cavity.

Like Rick said, some VW guys mill the wall out to get a larger float chamber. Since the 2-3lb fuel pressure doesn't flow real fast, some drag racers were running out of fuel on their pass. This helps that problem.

Really a non-issue on our cars - unless maybe you're drag racing a set of Webers.

Paul

[zrayr]

Originally Posted by PaulProe

".......To deal with this, the designer then cored out the area to reduce the amount of metal being poured.

Paul

I pretty much had the same thoughts. But I'd still like to know how gas is getting into the cavity . Sometimes it's half full, sometimes 3 carbs have gas there and one is bone dry. All kinds of different combinations with seemingly no pattern.

It just doesn't seem likely the top cover gasket is getting saturated and then the gas is wicked by capillary action into the cavity . These carbs are about two years old and part of a Weber set up purchased from Jim I.

Are the rest of you guys getting any gas in the cavity ?

Z

[Tom Howland]

I have the same thing happening. That makes me think gas is also leaking into the Venturi. That would be a good cause of tuning problems.

[Rick Parker]

Leaky gasket, no other way. During Braking or Acceleration fuel stacks up on the wall and leaks past the gasket void.

[zrayr]

Alright Rick, I'm going to break into the tune up kits I've got squirreled away and replace the cheap looking top cover gaskets with a set of brand new cheap looking top cover gaskets.

Z.

[Rick Parker]

The gaskets I have gotten have been pretty dried out and are a little difficult to get over the studs. Fuel in that chamber isn't an issue.

[zrayr]

Originally Posted by Rick Parker

The gaskets I have gotten have been pretty dried out and are a little difficult to get over the studs. Fuel in that chamber isn't an issue.

Probably not, but as was mentioned above, where else might the fuel be leaking into ? So new gaskets go on, and there might be some unintended benefit

Z.

[Gaz64]

I'd take the lids off, dry out the cavities, fill the bowls to the normal level, and observe over a time period how the weep is occurring.

If the weep happens while stationary, it must be porosity from the main well, or similar while operating the pump circuit.

[Rick Parker]

Sometimes the sealing surface of the lid is not absoluely flat and can be made so with very fine Wet or Dry sandpaper on a piece of glass. There may also be a little leakage past the pump squirters and respective O rings.

[Gaz64]

Originally Posted by Rick Parker

Sometimes the sealing surface of the lid is not absoluely flat and can be made so with very fine Wet or Dry sandpaper. There may also be a little leakage past the pump squirters and respective O rings.

I agree with you Rick, especially if the OP is running 00 pump exhaust valves.

[zrayr]

thanks for the ideas.

currently using the 0.50 acc. pump exhaust valves.

dried out the 3 "wet" cavities 3 days ago. Will replace gaskets and ck. over soon.

Z.