Float needle seat adjustment on Amal Mk2

I've been having fuel flow problems on my race bike & I think I've finally found the problem.

Stripping the Amal Mk2 carbs for possible crud in the system I noticed that the hole for the float valve seat was only about 1/16" dia, which I thought was way too small.

Checking with a friends Mk2's, the float valve hole was about 1/8", that must be where my fuel flow problem is. Why do Amal have the smaller float valve hole?

I drilled the hole out on my Mk2's to 1/8" & chamfered the edge. Because the float valve taper now goes furhter into the seat hole, the float height is now wrong. It is about 4mm (160 thou) above the surface of the float bowl surface.

I believe the float height (the farthest edge of the float away from the valve) should be 2mm (80 thou) below the float bowl surface. Is this correct?

How do you move the brass float valve needle seat to get the correct float height? How do I heat the bowl & to what temperature?

Do I then move the valve seat with a drift through the fual hose banjo opening end to obtain the correct float height? I gather this is trial & error to get this near correct?

Any suggestions would be much appreciated.

pouchy750 said:

Checking with a friends Mk2's, the float valve hole was about 1/8", that must be where my fuel flow problem is. Why do Amal have the smaller float valve hole?

Click to expand...

Different float needle seatings are used for different applications and there are 5 options for the Mk2 from 1.25-4mm. A carb fed by a fuel pump for instance, would use a smaller bore seating than one fed by gravity and a 2 stroke carb would probably use a larger size. [Edit: Apparently, 1/8" = 3.2mm is the standard 4 str. seating size, 1.6mm is for pump feed]

pouchy750 said:

I believe the float height (the farthest edge of the float away from the valve) should be 2mm (80 thou) below the float bowl surface. Is this correct?

Click to expand...

Again, I think this depends on the application. According to one Triumph service bulletin, the upper float surface should be parallel with the joint face.

pouchy750 said:

How do you move the brass float valve needle seat to get the correct float height? How do I heat the bowl & to what temperature?

Click to expand...

Just tap it either up or down, same procedure as for Mk1 (see Bushman's link). You shouldn't need much, if any, heat, gentle heat from a heat gun, or even immersing the bowl in hot water is probably enough as I believe the seatings were pressed in cold.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

An alternative to altering the seat would be to buy a pair of adjustable "StayUp" floats?


http://www.amalcarb.co.uk/ProductDetail.aspx?Id=37373