the Amal

As you've probably gathered by now, I love the MkI Concentrics, to me they are what a carburetter should look like and no other one ever looks quite right to me. I guess it's because I grew up with British bikes that pretty much all had these. The first A50 still had a 1" Monobloc and while I do love that one too, I decided that rather than buy one of those, which I would have done to make it look a bit quirkier, I would stick with the Mk1 concentric that came after (also, a new Monobloc is about 160 quid - a Concentric, I already have); if I'm not mistaken, they were introduced by Amal in 1967 and BSA went with a 26mm one, which is the closest to the original 1" size. While I do have the original 626 and I could have easily renovated that one, I also had a pair of 30mm ones from my Norton that were in pretty bad shape. I later got hold of other more-or-less complete used carbs and assorted bits and pieces in general that were going to be thrown away. I took them apart and put aside all the parts, selected the ones that had survived better and set to making one working carburetter out of the best parts I could find, as well as new spares and upgrades where needed. All the parts were thoroughly cleaned by my good friend Brian, who has an ultrasonic cleaner filled with a Marseille-soap degreasing fluid. The bits come out wonderfully clean and smelling like fresh laundry. Beautiful.
If you notice how the zinc alloy looks in this photo you can see it's bone dry after being cleaned:

This is perfect as it removes every little spec of dirt. I then treated all the parts with WD-40, once again proving to be a bit of a miracle product, and after that I oiled them, like a gun. After only a few minutes the metal was dry to the touch and the carb had taken on a wonderful patina. I then set about removing the original (short type) tickler, which was badly corroded: this is very common in old carbs.

The metal plunger had hardened to the point that I had to use a small file to remove the "mushroom" end that holds in in place.
I had salvaged an extended tickler from another old carburetter.

In addition to the plunger being much longer, and of course the shapely aluminium button, this tickler has a bush that fits in the carburetter body. With all the parts nicely oiled, it pressed in with no problems using the vice as a press. New plunger in, new mushroom end using a tapered punch and we're set.

With that done, I turned my attention to the idle circuit passages. WD-40 at hand again and air compressor at the ready (easy there, not too much pressure when you do this, ok?) I went over every passage, keeping another shut with my thumb, repeated this sequence a few times until what came out was just clean air. You'll know when you have it right, because the first time you do it you get this nebulised cloud of decades-old crud that had taken residence in your carburetter. Gradually it all disappears and your carb is ready to go again. If you think that you can get away without doing this, think again. Yes, if you're riding a drag racer then the idle circuit isn't that crucial, but on pretty much any other motorcycle, you'll want this to be in good shape and performing like it's supposed to.
The next thing I checked was the float bowl. These can be damaged if they're overtightened (something that happens easily when replacing the standard screws with allen bolts) so you need to put it on a flat surface and check if they're out of shape. In this case there was a little bit of distortion so I fixed it: to get a good idea of how the float bowl refresh/overhaul is done, I strongly recommend this two-part video: [http://www.youtube.com/watch?v=XIYgj5m9RW0 and http://www.youtube.com/watch?v=JHYnSua8ZZ0] and while you're at it, check out all his other Triumph videos too, he's great and a lot of that stuff applies to British bikes in general. Another thing I used to rebuild the whole carburetter is this kit:

New jets ready to go:

Nipped up with my trusty 1/4" Withworth spanner.

  

The float is of the new type with metal tabs, great for adjusting the level - something you just can't do (at least not easily: I have seen people bend the tabs using a lighter, etc.) with the standard nylon type.

Now, the new type of material (with metal tabs) was supposedly developed for use in Army Land Rovers as they needed to be as strong and reliable as possible, and is finally available for our beloved classics.

You can see the surface of the float bowl is all shiny after I sanded it. I checked again and it is properly flat now. The thickness of the gasket will take care of any unevenness on the carburetter body side, not that there is any, mind you.

Here's a new gasket and two brand new float bowl screws with split washers.

There, starting to look like a carburetter...

In addition, I fitted these extended brass screws which you can get from Lowbrow:

I punched a small reference mark on the air mixture screw. They look rad and they will make your friends jealous. Then it will infuriate them because they're not original, because they serve no purpose and various other questionable excuses, when really, they're just mad they didn't think of it first.

I managed to retain an original air filter backplate, which has a bit more character than a brand new one.

Other specs (these may change after I test the bike and see how the whole carburetter is working):

• Needle jet - 106
• Main jet - 220
• Needle position - middle groove

With all this new stuff, some of you might ask "wouldn't it have been cheaper and quicker to just buy a new carb?" Well, quicker perhaps (not with the recent delivery times though), cheaper? Certainly not, and that's the beauty of these things: you can refresh and throroughly overhaul your carburetter for years and years of reliable service.
The carb will ideally be mounted on an extended manifold, mainly because I really like the look of these. That depends on whether or not there will be enough room within the frame's main loop.

 

I love the fact that the Mk1 is such a small, delicate and essential part of the bike, one that can truly make the difference between something you'll never get sick of riding and something that will never ever be quite right.
Most of you know what I'm talking about, you try a bike that just doesn't do what it's supposed to and sometimes all it takes is a good clean and an overhaul kit and it's like you got a different engine. Think how small the jets are. Think how "flimsy" the whole float/needle assembly is, perennially balanced (until it punctures) and letting in just the right amount of fuel. It's all very small, precision stuff, yet those tiny jets are responsible for breathing life into the engine. Raucous, snarling, 'sploding life. In most cases these carburetters can last a long time if cared for properly. Don't believe the fearmongers who tell you that they will warp and melt and emit toxic radiation. Most problems found with Amals are down to careless owners who overtighten them, leave them full of gunk for a year, never change the gaskets and just don't know how to tune them. Ok, metal does wear, and in very extreme cases you can have slides that rattle a bit or stick in the fully open position (what a fun way to go though, hey?).
Amal have recently introduced a new hard anodised forged alloy slide that's supposed to be stronger and more resistant to wear.
I got one to try it and see what they're like, also because it could be a great major upgrade for others in my Club. Just looking at this I can tell you it is a great piece of machining, it looks absolutely flawless and if it works as well as it looks, we're in for a treat:

They also offer what they call the "premier" version of the Mk1, basically incorporating the StayUp float, the hard anodised slide and introducing an official version of a modification many people have been doing for a long time now, by drilling opposite the air mixture screw, in order to access the idle circuit. This makes it much easier to clean (and much more effective).
There's one more advantage here: the idle bush that was used on mark-ones until now has been replaced by an external jet that screws in opposite the air mixture screw. Anyway, you can read about it for yourselves here: http://www.amalcarb.co.uk/News.aspx?id=54

It was like an Amal-themed Christmas morning at the garage!

There's something about this photo that makes me think of a rifle:

New needle and clip:

Yes I realise it still needs actual cables, I'll do that when the bike is done and ready to be fired up and let loose to terrorise the village.

I decided to go with a couple of Allen bolts for the top cap. Bizarrely, they have a 4mm socket. You have to be careful with these because since they can be tightened so much more than the original screws, it is all to easy to warp the zinc-alloy. I re-used a couple of split washers from two old screws that had badly damaged Phillips heads.

Doesn't it look like a model spacecraft like this? The HMS Concentric...

After I was done with the carburetter, I went through my stock of Amal spares - I really have a lot now - and picked a few essential things that I'll keep with the BSA. There is a spare float, springs, float bowl screws, an air mixture screw, spare jets, a fuel filter and a new set of gaskets: bring it on, road-side repair! It all packs neatly into a small hard plastic case that I think I'll keep in the toolbox I recently got.

Now, if your Amal is giving you trouble, don't just throw it away for another make, thinking there is nothing to do about it and that it will never work anyway - fix it. Figure out what's wrong with it, use the troubleshooting guide provided (you can download all you need from Amal's website) and fix it. Besides from the fact that you can replace every single component individually, if your carburetter is damaged beyond repair by decades of abuse, you should consider replacing it with a new carb, built to your specifications by Amal and just be done with it.
Your new carb will last for a very long time and give you countless miles of dependable service. I would strongly recommend against replacing Amal for another make - any make - as they are the unsurpassable best for British bikes (and others, even Ducati at one point).
Long live the Amal.