450 desmo carb

[themoudie]

Morning Colin,

I too used that combination of radiator hose and two aluminium manifolds (thank you for using the correct terminology ), with an AMAL MKI 932, from 1977 up to the present incarnation.

Marine fuel hose was my original intended connector, but with the ignition nonsense and the new carb combination, I wasn't sure if the downdraft angle was causing, or contributing to the running problems and used the cranked Triumph TSS inlet rubber instead, so holding the carb at a more horizontal angle.

Although I haven't got the scales out, I suspect that the AMAL MKII is heavier than the MKI and having this weight flapping about due to the induction pulses and centrifugal forces coming from the crankshaft, it is proving too much for the rubber. I do use wide Jubilee clips to hold everything together. Hence, the two tapped holes at the top and rear of the MKII carb body!

I'll keep you posted.

Good health, Bill

[Jordan]

two aluminium manifolds (thank you for using the correct terminology )

Careful, I'm an unrepentant pedant.
What's "manifold" about an inlet stub on a single?

[themoudie]

Afternoon Jordan,

Point taken, Wikipedia "The word manifold comes from the Old English word manigfeald (from the Anglo-Saxon manig [many] and feald [repeatedly]) and refers to the multiplying of one (pipe) into many.".

So, inlet stub it is!

Good health, Bill

[Jordan]

That's gracious of you to concede, Bill.
Most people say manifold, but there's no harm in being accurate.

[themoudie]

Aye Jordan, I can be a bit of a pedant myself on some things.

As for the marine fuel hose (MFH) test that appears to have been successful. Because of the wire spirals (2) and the double cotton canvas reinforcing, there is little flex in the 48mm length that I am using, along with wide Jubilee clips. The whole assembly appears virtually rigid, unlike the bobbling action of the carb when using either the pattern Triumph TSS inlet rubber, or an AMAL OME straight inlet rubber. Induction pulses and crankshaft dynamics are really noticeable, even at tickover, with this engine.

The major problem, as this is a 450 MKIII, are the reinforcing webs welded to the frame, right where the bellmouth wants to sit and also the overall diameter of the carb (AMAL 2932) screw cap top, which means that the carb has to be tilted slightly to the right so that the screw cap doesn't foul the frames large diameter spine tube. Using the cranked TSS inlet rubber solves these problems, by holding the carb so that the slide and needle are vertical and the float bowl upper edge is horizontal.

With the canted position using the MFH, I suspect that I am likely to get even greater wear on the needle and the needle jet than when they are held vertically. Maybe another reason to revert to George's favourite AMAL MKI 932 or Premier version.

Good health, Bill

[Duccout]

Aye Bill, clearance is always a problem, even on my 350 Mk111 I had to lift the rear of the tank up to clear the top of the velocity stack (a name right out of Bonneville!). I suppose that is a good reason to stick with the Ducati manifold/ Dell'Orto combination which puts the carb in a nice clear position in the frame; they are not stupid these designers. Let us know how you get on.

Colin