CA006 CARBURETTOR

My 1964 MSS was rebuilt some years ago personally by Ralph Seymour. I have used it very little since that time mainly because of hot starting difficulties. It has now been fitted with an electronic coil ignition systen by Kirby Rowbottom and it starts a treat - Whoopee! I now find that I have some problems with the Amal concentric carb. fitted by R.S.
Firstly - it can only be nipped up VERY gently otherwise it distorts and jams the throttle. I worry lest it should vibrate loose or even fall off. Secondly I suffer quite often from flooding and stopping while on the move because either the the float is sticking down occasionally or the float needle is not rising enough to cut off fuel supply. Or could it just be crud in the tank?
I note that the movement of the float up and down from open to closed is very much less than on older designs of carb. which I have been used to. Have you any comments.
Finally - is there any mileage to be gained by fitting a Jap. - say Mikuni - carb. If so which type and would any other mods be necessary - and what jet settings? I am not a purist and just want decent reliability, easy starting and good economy. Touring speeds of say 50 - 65 m.p.h. are quite high enough for me nowadays! Any mods should be easily reversible by any future owner who may value originality. - Marcus Hasted 31/8/2004

My thoughts are: Something is a bit wrong if your carb distorts in the way you describe. If your concentric has an O-ring then light tightening and loctite may work OK, but I wonder if either the O-ring is too large or the flange on the head isn't flat. Either would result in distortion. I think the M180/2 heat-insulating spacer gasket should still be fitted with a concentric to avoid heat getting to the carb and with this lightly tightened onto the manifold with extra washers replacing the carb you might be able to detect any gaps indicating that the inlet flange isn't flat. Then try the M180/2 against just the carb (initially without the O-ring in place) using some short bolts and gradually tighten their nuts which should let you check the gasket for gaps implying the carb flange isn't flat, then try with the O-ring in place and check the M180/2 doesn't warp before it is flat against the carb flange (if it does, then the O-ring is too thick and the carb would distort - you can either find a thinner O-ring, or rub it down, or try without it using a modern sealant or very thin paper gaskets.)
The float doesn't move as much as on the earlier carbs. If it was just flooding it could be dirt or a poor seal at the needle tip (use a "vitron" tipped one from one of the Amal suppliers), but if it also sticks shut that does imply a stiffness in the motion of the needle or float (rather than dirt) so start by carefully polishing the bearing/sliding surfaces of these two parts - the sides of the needle and the float spindle parts. It may just be a coating on the inside of the needle housing through lack of use, but you have to be very careful cleaning this out. Or as you say it could be a bit of grit in this housing making the needle stick.
I'm afraid I've never seen any published settings for alternative carbs on an MSS, but the Carb specialist advertisers could supply one with the right equivalent settings to those for an Amal. - TW 31/8/2004

I thought to phone Kirby Rowbottom after I mailed you and your reply confirms Kirby's opinions and recommendations to the letter!
He always discards the O ring and also insists that I get a vitron tipped brass needle. This I have ordered today from Surrey.
Kirby also recommends the Mikuni and has strongly suggested that I consult Allens of Nottingham who are the most knowledgeable in this field.
I shall do so on my return from the Goodwood revival meeting this weekend. - MH 1/9/2004