Hitchcocks Forum

I have the Amal 376 on my 500 twin.I had it cleaned with an ultra sound cleaner and it worked well for the first few hundred miles. I now find whenever I leave the bike unused for a few weeks the slider sticks solid. I can free it with WD or paraffin but then next time I go to the bike it's solid again. Any advice please?

Not sure about the monoblocs but I know I have had terrible bother on my Mk1 concentric due to the throttle valve being made of the same alloy as the carb body. This has lead to extensive scoring and wear on both the slide and the carb body to the point the bike will barely start and the carb is essentially scrap. The solution would have been to fit a hard anodised slide from new but I didn't know this when I bought it.



If the problem is alloy corrosion sticking the slide in the carb body (you're sure it's not the cable that's sticking?) I'd imagine a hard anodised slide would be much less prone to this problem. You may already have one mind. The anodised ones are black in colour, standard ones are silver.

You have probably over tightened the mounting bolts which will cause the same problem.
Always remove and replace the carburetter fully assembled, with the float chamber and mixing chamber lid, throttle cable and slide components installed. This ensures maximum rigidity of the assembly while it is being installed.

Tighten the mounting nuts carefully and evenly. Nuts and spring washers should be tightened until the spring washer is just flattened. Over-tightening the nuts will over-compress the flange gaskets at the flange extremities and may warp the flange, and in extreme cases the carburetter body, causing the throttle valve to stick.

Mark 1 carburetters are not designed to bolt tightly to the intake flange and may distort if overtightened. It is only necessary to compress the O ring seal to ensure air tightness. When correctly tightened the carburetter flange and engine manifold should be no more than just touching. Nyloc nuts should always be used to mount Amal Mark 1 carburetters.

Haggis has it.......virtually all the problems I've encountered personally with Amal carbs. are directly attributable to some previous owner's ham-fistedness, particularly in respect of overtightening. It is possible to straighten a bent flange on a Mk1 Concentric (with the correct technique and equipment) if the amount of distortion is not too bad, but further damage can frequently be caused to the mixing chamber cap and float chamber from overtightening. Any attempt to fix distortion of the flange by filing, sanding, etc. merely aggravates the problem as you are then left with a thinner flange which will warp even more easily, and ruins the fit of the flange 'O' ring, if fitted. Monobloc carbs. enjoy a better reputation generally for quality and service life, but if original fitment, many of these would be over 50 years old.......

Sticking slides are not peculiar to Amal carbs. - the last one I had to deal with was in a Keihin carb. on a Honda. This has a bushed x-shaft in the top of the mixing chamber, and a cable drum with push-and-pull cables to operate the slide - i.e. POSITIVE opening and closing of the throttle. A precision instrument - slide-to-body fit is something you could only dream of with an Amal. Of course, this ensured that freeing off this stuck slide without causing damage was extremely difficult, and took weeks of soaking in fuel/penetrating oil/WD40 - you name it. The actual cause turned out to be nothing more than residue/gum from old fuel.

If its a modern Amal the tolerances are pretty dreadful. I have a pair of replacement concentrics and if you swap the slides one of them sticks open!

You can get a hard anodised slide for the 376 which might perform better

OK All, thanks for those comments. I'll have a look at those and see if I can remedy the problem. Rod

Second that Vaslsp, modern Amals are pretty awful, even Mikuni copies are better. I think people fit Amals 'cos they look the part but there's no advantage.

The current producers of the Amal Mk1 Concentric recognised that all was not well and brought out what they call the Premier version, they're supposed to be quite an improvement, aluminium alloy instead of zinc alloy bodies, hard-anodized slides and detachable pilot jets. Has anyone here tried them?



A.

Pick up amal carby drop in waste bin buy jap mikuni fit and live happily ever after.