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Thread: Sleeving Vintage Amal carburator

  1. #1
    thirdbike's Avatar
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    Sleeving Vintage Amal carburator

    Was wondering if anyone has ever resleeved the slide bore of a carburetor. The Amal concentric carburetors were used on vintage British motorcycles and, in fact, they are still available today. The problem is that they are made from a relatively pot metal (not aluminum). The slides are made from the same soft material. The result is a galling action leading to wear which leads to improper fuel mixtures. I would like to ever so slightly over-size and true-up the carburetor slide bore. The slide would be turned down and a brass sleeve affixed to the slide. My thoughts were that a reamer would do a more exacting job than trying to bore on a lathe. An aluminum cylinder with simple steel cutters set in the cylinder should do the job with perhaps a center shaft protruding into the needle seat hole to ensure alignment. This entire operation could be done by hand and a reamer would provide a cleaner finish. As for turning down the slide, I haven't come up with a more simplified technique Both the bore and slide are round of course. If it were only one bike I might take the plunge and buy a set of the new Premier Amal carbs. They, like my effort have a dissimilar slide but with several vintage bikes the cost begin to become prohibitive. I thought it would be worth the try as i have a couple of worn spare carbs to experiment with. There used to be a few old chaps around that did resleeving but they have taken their secrets with them.
    Any ideas and suggestions would be much very appreciated. Thank you

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    Frank S's Avatar
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    I was sitting here trying to remember the wall thickness of my old Amal 28s on my 73 850 commando I used to have. The Amals had become so badly worn to the point that performance had dropped to near zero I mistakenly thought I wanted to adapt a pair of Mikuni 32's to it then had to down jet them. power was back in over abundance after an IGN upgrade combustion chamber clearance shave only .008" wound up replacing the clutch pack with a Barnett added a disk as well then came the primary chain upgrade which led to a 5 sp transmission then a 30 mm wider tire in the end a botched up looking and acting bike that would eat a KZ 1100 for breakfast lunch and dinner in the 1/8 or 1/4 Should have just rebuilt the Amals or bought new ones. (Available back in 1980.) If I had I might have kept the bike.
    For sleeveing or bushing I am wondering if it would be possible to use an exothermic metalizing spray to do the build up. I can see this working on the slide but the smallness of the bore that might be impossible. I know there are coatings which can be applied to racing pistons to reduce friction they have a minimal build up factor
    which may be a possibility for the bore and slide to build them up without having to sleeve the coating then could be honed or polished back to spec.
    Might be worth looking into.
    Never try to tell me it can't be done
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    From British bikes many a mechanic was made. The wall thickness on the Amals is already on the thin side. We're talking only a couple of thousands to true things up for those who might be wondering.
    I had thought that some kind of coating on the slide would work. I had considered plating the slide. Amal did have replacement chromed slides but these were recalled as the chrome had the bad habit of flaking off. The new Premier carbs have anodized slides. The problem of course is that the bore is now oversized due to wear.
    Thanks Frank

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    Hello !! I havent resleeving an amal carb but i reore it on my sb lathe many years ago for my Royal Enfield bike , the fact was i take a few thousandscand made a new curtain i aluminium and still works fine , and extra consideration is to made new ways on the bronce block because if they are worn out makes the curtain twist and gives a very erratic idle .
    Your idea to fit a sleeve is very intresting it could be nice to fit it loose and hold it with loctite to avoid stress on the pot metal then made a mandrel an hold on the lathe to exact boring
    Hope it helps !!
    Regards
    Andrew from Argentina
    Wasap +542914674259

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    A friend in the Tucson area was turning down Mikuni slides for Amals. I had a BSA 441 Victor that I used one of his slides on it and never had any more trouble. I didn`t do anything to the carb; just dropped the sllide in. I see now the shop he was turning them out for is still in operation and mentions turning the carb body too. Here`s a link to their process. Concentric Modification

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    I assume that you are doing a restoration. If not, set the AMAL concentric aside and use a decent carb. I used race a 750 Triumph twin back in the 1970s and used a pair of 32mm Mikuni carbs. Some riders were using Dellorto carbs from Italy. Sorry to the Brit bike lovers, but AMAL carbs were sh-tty. If you must use an AMAL, I would suggest trying to find one in better shape rather than trying to sleeve a worn-out one.

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    Thanks, but I sold all my BSAs several years ago and just sold my Harley Davidson last year. I somewhat reluctantly got out of the motorcycle scene after riding for 55 years. I did have a `65 A65 with a single carb. I replaced the Monobloc with a Mikuni 32 the day I was riding it work and smelled gas and looked down and it was spurting a stream on my leg. I`ll be the first to admit the Amals were shitty carbs. At least the concentric was an improvement over the monobloc. It was probably designed by Joseph Lucas, too, lol. (Known in British bike circles as the Prince of Darkness)
    Last edited by baja; 06-19-2018 at 06:18 PM.

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    Thank you for the replies guys.
    I know that with a set of Mikunis properly dialed in, the bike will run better. To my thinking it defeats the purpose somewhat. I might as well buy a new model bike which I already have anyway. These old bikes don't have an electric starter, they don't have as much power, the brakes could be better and they leak oil but it is a hobby resurrecting these old girls.
    Andrew from Argentina, I am not sure exactly what you did. I realize that there is a language issue. Perhaps you could try and explain once more what you did. You made mention of an aluminum curtain. Was this aluminum piece something that was sleeved to the perimeter of the slide or did you insert a sleeve in the bore? Perhaps you could explain in a bit more detail what you did.
    Baja, your chap at the linked site uses a chrome plated slide. As mentioned in my reply above, Amal started out with an improved slide that was chromed. The problem was that with time the chrome started flaking. Chrome flakes sucked into the motor is not a good thing. The other issue is that aside from the cost of sending out six carbs, I would like to keep the carbs as stock as possible whereas this chap modes the slide so that the choke can no longer be used.

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    Sorry my poor english , the proper name was slide instead of curtain , in my case im just rebore a few thousands in the lathe and made a slide of camplo ( kind of aluminium ) and works very well .
    I wonder wich carb you have and in wich bike you fit it .
    Excuse me thirdbike whats your name ?

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    Not sure if they still do it, but brake repair companies used to sleeve brake and clutch cylinders to reclaim them and actually make them better than they originally were. It might be worth talking to one locally to see if they still do it now. My experience with several of those Amal carbs was that the threads holding the top cap on often unscrewed or just popped off. e.g. 1960 Norton only 3 years old, straight off ferry at Calais, never driven on the right of a road before, opened throttle, cap popped off and bike accelerated to near full speed up the main street, through intersections, red lights etc etc and no idea where I was going. Key was in chest pocket of and anorak I was wearing, so only option was to turn fuel off while dodging cars with one hand on handlebars. Bike eventually used up the fuel in the bowl and stopped outside a bakers shop. It was surprising how much distance it travelled on a bowl and hose full of fuel. Sat down in the gutter for about an hour after that with fresh baking and coffee to calm my nerves.

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