On The Bench - Amal Monobloc Velocity Stacks

These velocity stacks were actually given to me a while ago, and they were in about as rough of shape as one could imagine. The tips of them were ground down in places and there were gouges all around the inside and outside of them. It looks as if someone had been tightening them onto the carb, using channel locks. It makes me wonder what sort of owner would wrench on their bike in such a fashion. I know there are plenty of hack mechanics out there, and that these are old parts, but damn, I can't imagine you could treat something this rough.

My buddy put these in the his lathe and trimmed off the tips of them in order to remove the gouged sections, and also to shorten them slightly in order to have enough clearance for the tight fit on a Norton Atlas. Once the carbs are mounted, there's not a lot of room between the carb inlet, and the oil tank / battery box, so these were the perfect candidate to be trimmed down for this application. Without doing a bunch of work to these stacks, they were literally garbage, but I knew that I could likely save them.

Here's the before shot, after they had been cleaned and trimmed down on the lathe. I don't think this photo does justice to how poor their condition was.

I sanded out all of the gouges, or at least as many of them as could be removed, and then polished them inside and out. Obviously that's just a cosmetic thing, but now they look nice enough to go on the bike, once I get around to buying the carbs. They're certainly quite presentable, and saving these, sure beats throwing them away and replacing them.

A couple things to note; these are for 389 Amal monobloc carbs, which is the correct fitment for my Norton. These stacks aren't interchangeable with the 376 Amal monobloc, or the Amal concentric, so if you're looking for velocity stacks on eBay or something like that, please double check that they're the correct fitment. There are plenty of different versions that have been produced over the years. They come in different lengths and shapes. These are the straight type, but some have more of a bell shape, and some even come with mesh screens, which is a nice addition. The carbs on a Norton are so close together side by side, that I don't believe the bell shaped velocity stacks would have enough clearance. Wassell made and sold a lot of these as aftermarket parts, and they stamped some of them in order to make them easily identifiable. You'll see stampings like "389 / 2 1/4" which is of course for a 389 monobloc, and an overall length of 2 1/4".