Monobloc sealing and mounting

[Tigerfeet]

I'm now puzzling over my monobloc that I have just fitted with a 'stay-up float'.

How should I seal the float chamber. I have a new gasket, and was reaching for the 3 Bond - and realised I was just guessing. Would (should?) it seal dry? Or with just a bit of grease on the gasket?

That led me on to thinking about mounting the carb to the cylinder head. Its a 1966 C15 with what I believe to be the original carb. This has the large 'O' ring. I have a multitude of manifold gaskets, but I'm not sure whether a gasket is required at all. With the 'O ring, surely that is the seal.

I found this text on the Burlen Amal site: Where the thicker O rings are used, on early Monoblocs and some Mark 1 carburetters, the nuts should be tightened until the clearance between the carburetter flange and the manifold surface is no less than 0.025 inches at all points.    If I am supposed to measure that gap, the implication is that there can't be a gasket.  (I've mounted countless Amal carbs over the years with 'O' rings, gaskets, sealer etc.... And now with the internet I'm finding everything I 'know' needs questioning....)  Does anyone know for sure?

[limeyrob]

Float chamber - dry, the seal surface is quite thin and if its not dry I find it can slip out of place as its assembled.
O ring - check the flange is flat, these get overtightened and bent, hence the warning about 25 thou, although that looks a bit large to me, perhaps fine on a new flat carb.  I fit O ring carbs with no gasket.

[rhyatt]

Dont forget the manifold heat gasket to keep engine heat from carb

[iansoady]

Original float chamber gaskets were much thicker than the ones that seem to be around now. I find the later ones hard to seal and sometimes resort to a thin smear of wellseal.

[Tigerfeet]

You are right. 40-0320 Tufnol.  I've just found one on eBay - so that is on its way...  I wondered how the rubber 'O' ring dealt with the heat of the cylinder head - but that explains it.

[Tigerfeet]

This was my manifold straightening rig. Left it like that for about a month...  It has remained straight since.

[limeyrob]

Good reminder about the tufnol spacer, they make a big difference. Gasket between the head and spacer but not between the spacer and carb if its got an O ring.
Agree about the float chamber gaskets, the last one I bought was about half the thickness of the old one.

[neil1964]

This was my manifold straightening rig. Left it like that for about a month...  It has remained straight since.

I did not know that Monoblocs had that issue. I thought that it was just Mk1 Concentrics.

[cdsdorset]

This was my manifold straightening rig. Left it like that for about a month...  It has remained straight since.

I did not know that Monoblocs had that issue. I thought that it was just Mk1 Concentrics.

It depends if the right mounting bolts have been used.

[limeyrob]

I don't think it so much a problem with the carbs as with the owners overtightening. It leaks, they tighten, it bends, it leaks more and so on.