Throttle springs

[Minto]

I've been battling with throttle cables for a couple of hours this morning, carb on, carb off, carb on, carb off like some petrol soaked karate kid. Trying to cure a sticking throttle on the 276 premonobloc. Anyway, eventually decided that the return spring is too weak so am going to order a new one only to find out that there are two options, a long spring and a short one. (As well as the air slide spring).
Does anyone know which spring I'll need? The Burlen site lists them as part numbers 4/037 for the short spring and 4/263 the long one. There are no details of the length of either.
I'll probably order both as they're cheap enough but if I can avoid more messing about and fit the right one first time that would make a very nice change.
For the time being I've fitted a tiny washer above the spring which has cured the fault for now, so a stiffer spring will definitely sort the issue.
Thanks team.
Jase

[Slymo]

More likely to be a distorted body from over tightening the flange nuts.or the jet block nut. There should be no noticeable friction in the slide. Try loosening the aforementioned to see if that frees things up. It is crucial not to over tightening things on these carbs especially the jet block nut particularly as it can distort and bell the body making the fit between the jet block and the body loose which stops the idle circuit working.

[Minto]

Cheers Slymo
I'm beginning to think that could well be the case, the carb doesn't seem to respond much to alterations of the air screw so is probably idling the needle jet. Apart from a slightly fast idle, and the running a bit rich it's going way better than it ever has since I've owned it so I'm a bit reluctant to mess with it much for now. The sticking throttle seems to have been sorted now. Certainly can't afford a new carb at the minute.

[Slymo]

Ok that does sound like the body may have distorted a bit. The jet block may feel like a tight fit but it is likely to be just pinched at the bottom. What I suggest is that you take the carb off and pull out the brass jet block by removing the big nut that the float bowl sits on and then knock out the jet block with a suitable piece of dowel or similar. You can see when the jet block is removed that there are galleries that run between the jet block and the mazac body. If there is any air gap there the idle circuit won't work properly and the idle mixture screw will have little or no effect. If you have a nice small steel rule or similar straight edge you should be able to see if there is a distortion and if there is then I recommend relieving the body at the bottom where it is pinched in with a careful scraping using a Stanley knife blade or similar. You'll find just relieving the bottom edge means the jet block will now drop in loosely and now you can shim it over to ensure a tight fit where the gallery holes are with a bit of brown paper thick enough to make it a snug but not an overtight fit. Another way of testing the fit is to use some Engineer's Blue on the jet block and push it is and out of the body. If there is no sign of blue in the body other than at the bottom is is case proven and you get to work with the scraper.
You then reassemble making sure not to overtighten anything. Mazac or Zamac or muck metal or whatever you want to call it is very prone to distort with excessive use of the spanner and whilst it is counter intuitive not to make everything on a bike tight as possible it is crucial on any Amal carb.  I've resurrected several old 276 and 29 carbs this way and it is deeply satisfying to have them respond appropriately to the air screw from rich to lean in a couple of turns.  Good luck and keep the faith. It's very tempting to give up and go to a new carb but nothing imho looks better than the age appropriate device.
 

[Swarfcut]

 I'd add to Slymo's excellent instruction.  Warming the carb body gently with a hot air gun aids removal of the jet block. Like  the magneto, they don't like too much 'ommer and a little bit of heat helps in this case, expanding the body and softening any gummy deposits.

 Swarfy.

[Minto]

Slymo and Swarfy, thanks for the great info.
During the recent rebuild I did strip the carb to its component parts, including pressing the jet block out with the aid of a big vice, thick dowel and big socket. I gave everything a good clean and blew through all the little holes and jets with a can of carb cleaner, at one point dislodging a lump of beetle shell!!! Nothing looked distorted or misaligned to my untrained peepers.
When I put it back together before putting the float bowl back on I sprayed carb cleaner through the pilot hole on the bottom face of the jet block which then exited through the hole in the carb body at the flange side, so assumed things were lined up correctly, but if the body is distorted then I suppose it's dragging air in from around the block rather than the air screw hole.
I'm in Wales at present on holiday (bike running great so far). But when I'm back I'll get the colourtune on it, and if necessary get the straight edge and scraper on it.
My replacement spring should be at home now, (only ordered it 3 weeks ago!) so the carb will be coming off anyway.
Thanks again for your help.
Jase