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?
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.
Dont forget the manifold heat gasket to keep engine heat from carb
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.
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.
This was my manifold straightening rig. Left it like that for about a month... It has remained straight since.
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.
Quote from: Tigerfeet on 08 Mar, 2026, 12:56 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.
Quote from: neil1964 on 08 Mar, 2026, 18:15 Quote from: Tigerfeet on 08 Mar, 2026, 12:56 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.
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.