Any Weber carburettor experts?

[The Surveyor]

After the great joy of getting my Maserati Mexico started for the first time yesterday, I noticed petrol seeping out of from the gaskets to the insulation blocks at the base of the carb's.

I've pulled off the carbs this morning and found that each of the insulation spacers have a slot in them which looks to be where the petrol was coming out.



Now I'm not an expert, but this just doesn't look 'right' to me although each base has the exact same slot and they look 'factory', and not cut as a DIY bodge.

Anybody seen this before?

[The Surveyor]

Oh and for reference, the carbs are 38 DNCL5 Webers.

Cheers

Paul

[marshalla]

"for the first time".

How long has it been standing ?
When were the carbs last overhauled ?
Have you checked internal carb. seals, gaskets and float levels ?
What sort of fuel pump are you using ?

Edited by marshalla on Sunday 17th August 15:36

[The Surveyor]

marshalla said:

"for the first time".

How long has it been standing ?
When were the carbs last overhauled ?
Have you checked internal carb. seals, gaskets and float levels ?

Carbs are fine and not what's causing me any concerns as they were refurbished before I bought the car although it has been 3 1/2 years since it last ran. The thing that does concern me is the slot in the insulation plate. Should it be there or not as surly it should be sealed below the carb?

Paul

[marshalla]

The Surveyor said:

Carbs are fine and not what's causing me any concerns as they were refurbished before I bought the car although it has been 3 1/2 years since it last ran. The thing that does concern me is the slot in the insulation plate. Should it be there or not as surly it should be sealed below the carb?

Paul

I disagree - fuel should not come out of the mounting area if the carbs. are fine. It suggests there's an overflow or leak somewhere inside the carb. which is causing fuel to discharge somewhere that it shouldn't. Last time I had it, it was because I had a leaky float which was allowing one carb. to continue to flow even when the float chamber was full (the float had sunk and wasn't closing the inlet valve).

As for the slot - Maserati may have designed it that way to allow air into the inlet. Funny thing to do, but that's the usual effect if the mounting isn't tightened up enough - not fuel dripping out. Or it may just be there to accommodate compression effects as the mount is tightened.

[The Surveyor]

marshalla said:

I disagree..

As for the slot - Maserati may have designed it that way to allow air into the inlet. Funny thing to do, but that's the usual effect if the mounting isn't tightened up enough - not fuel dripping out. Or it may just be there to accommodate compression effects as the mount is tightened.

Sorry, what you're saying doesn't make sense. The fuel is not coming out of anywhere on the carbs, the carbs are fine. Fuel is coming out of the slot in the very solid non-compressible insulation plate.

Anybody seen carbs mounted on insulation plates with slots cut in them?

Paul

[marshalla]

The Surveyor said:

Sorry, what you're saying doesn't make sense. The fuel is not coming out of anywhere on the carbs, the carbs are fine. Fuel is coming out of the slot in the very solid non-compressible insulation plate.

Anybody seen carbs mounted on insulation plates with slots cut in them?

Paul

So the fuel is passing through the carbs. By the time it gets to where those plates are it should be in aerosol, not liquid fuel, and only flowing when it's called for by the vacuum or pumped through by accel. pumps.

If it hasn't run for a while, I'll bet on a sticky float valve passing fuel and overflowing.

Edited by marshalla on Sunday 17th August 16:30

[stevieturbo]

The Surveyor said:

Sorry, what you're saying doesn't make sense. The fuel is not coming out of anywhere on the carbs, the carbs are fine. Fuel is coming out of the slot in the very solid non-compressible insulation plate.

Anybody seen carbs mounted on insulation plates with slots cut in them?

Paul

What he's saying, is that regardless of that slot, you should not be getting fuel in there in the first place for it to run out.

When you shut the engine off, no fuel should pass through the carb in order to leak out, and when the engine is running there should be vac there, so again it should not leak fuel out. Although it is possible a small amount could.

But I also hear what you're asking....ie WTF is the slot for ? And I havent a clue.

[The Surveyor]

stevieturbo said:

What he's saying, is that regardless of that slot, you should not be getting fuel in there in the first place for it to run out
But I also hear what you're asking....ie WTF is the slot for ? And I havent a clue.

Just to add, the fuel is only present when starting, I gave it a few squirts on the throttle to prime the carbs, neat fuel down the carbs..... That's when the fuel was seeping out of the gaskets / insulation spacer.

I just can't understand why there would be an engineered vent slot through the spacer

Paul

[Ian_UK1]

The Surveyor said:

I just can't understand why there would be an engineered vent slot through the spacer

Paul

Seems odd - and of course, the slots will be allowing unfiltered air into the engine. I can't imagine any competent engineer doing this deliberately.

Is the shape of the mounting plates a 'standard' Weber fitment or are they unique to the car? If they're a standard Weber size/bolt pattern, just get some without the slots.

[The Surveyor]

Ian_UK1 said:

Seems odd - and of course, the slots will be allowing unfiltered air into the engine. I can't imagine any competent engineer doing this deliberately.

Is the shape of the mounting plates a 'standard' Weber fitment or are they unique to the car? If they're a standard Weber size/bolt pattern, just get some without the slots.

Thanks, They are a standard weber bolt pattern so I will replace with new along with new gaskets.

It the reason why anybody would do it that I also don't understand. Was it a bodge to compensate for crappy Italian fuel or some other reason to ensure the car ran lean. Especially confusing given that the slots are very neatly cut and are perfectly lined up, not just hand-cut with a hack-saw! Strange

Cheers

Paul

[stevieturbo]

Although the slots themselves dont actually appear to go right into the inlet path ?

Once a gasket is over that face, the port should be sealed...barely, but still sealed ?

[Sensibleboy]

I thought carbs fitted to manifolds using misab plates to seal them?

[marshalla]

Sensibleboy said:

I thought carbs fitted to manifolds using misab plates to seal them?

That's one way of doing it - but can be a bit prone to vibration if they aren't mounted correctly. (Not hard to get right, mind you - just needs the proper rubber cup washers either side and a set of feeler gauges to set the gap).

I guess for factory fitting, the rubber blocks were easier as they didn't need much in the way of "setting".

[The Surveyor]

marshalla said:

Sensibleboy said:

I thought carbs fitted to manifolds using misab plates to seal them?

That's one way of doing it - but can be a bit prone to vibration if they aren't mounted correctly. (Not hard to get right, mind you - just needs the proper rubber cup washers either side and a set of feeler gauges to set the gap).

I guess for factory fitting, the rubber blocks were easier as they didn't need much in the way of "setting".

Just to let you know, blocks are a hard bakelite material and I understand are there to act as a thermal break between the manifold and carb, presumably to control any vaporisation. These are off a 45 year old car so wouldn't have used a misab plate but I have found out from a classic Maserati specialist today, that the slots are certainly not standard!

Cheers for the input guys.

Paul