Neil: I would check the pilot jet. If it is blocked the bike will be hard to start and will not idle properly, if at all. This requires removing the jet block.
When new, the jet block was a nominal fit, and would almost slip out of the body, with age they seem to get sticky.
Avoid the urge to push the jet block out of the body by pressing, or tapping, on the top of the jet block. The sides that form the venturi are thin and bend EASILY!!!!!!!!!!! This will render your jet body useless.
Remove the Mixing Chamber Union Nut that retains the Jet Body. Warm the bottom of the Carburetor body and insert your thumb or finger into the venturi and press down on the jet block. You will need to protect your hands from the heat.
If this fails a small puller can be made from the Mixing Chamber Union Nut, stiff washer to support the head of the bolt on the hole in the Mixing Chamber Union Nut and a 1/4 x 26 tpi bolt. Put the Mixing Chamber Union Nut back on the carburetor until it seats against the Jet Body. Back the nut off a bit - 1 1/2 to 2 turns. Insert the bolt through the washer and through the Mixing Chamber Union nut and screw it into the Jet Body so the threads are fully engaged in the Jet Body.
With the body still warm tighten the bolt to start pulling the Jet Block out of the body. Remember you only have 1 1/2 to 2 threads clearance to work with so one turn, or a tad more, of the bolt is all you should expect before the Jet Block hits the Mixing Chamber Nut. The aim here is to loosen the Jet Block so you can push it out with your finger. You can take another turn on the Mixing Chamber Union nut and get the Jet Block to move a bit more.
Remember this stuff is fragile and parts are expensive!. The jet is in the back side of the Jet Block and is usually .020". It is located at the bottom of a small drilling directly opposite the passage leading to the feed hole located just behind the rear of the slide.
Go slow, and if things don't appear to be going your way - walk away!
The Idle Spray Tube in illustration above, is actually the secondary orifice and because of the differential in pressure between the orifice behind the slide (high manifold vacuum) and the front edge of the back of the slide (atmospheric pressure) actually draws air into the circuit at idle. Once the slide is lifted, and the pressure evens out between the two holes, they both provide fuel.
This secondary Idle orifice is not in all early AMAL remote float carburetors. A lot of the early ones only have one orifice behind the slide, and not illustrated above. John
Hi. I love the diagram of the 276 jet block. Its the only one i have seen that shows the details of each of the openings. can you tell me where it came from. I am trying to determine where the fuel inlet in the base opens to? I think mine is blocked. The mixing chamber on mine is a shallow depression that opens with a very small opening up into the main tube and a small hole heading down into the secondary inlet. How do i unblock the fuel inlet. I have tried blowing it out with air but it doesn't seem to open anywhere at the top (when standing on its base) of the inlet. Appreciate any help you might provide
Hi Andrew, The fuel inlet in the drawing (brown vertical passage) is often blocked by the fitting of an incorrect fibre /paper washer between the jet block and union nut the hole in the washer must be large enough to allow fuel to reach the opening A tiny hole in the "mixing chamber" links to the vertical passage and also to the idle spray tube This drilling is in effect the pilot jet You need to remove the jet block to access the mixing chamber. another tiny hole in the carb body leads from the "mixing chamber" to the engine side of the throttle slide