1954 NH 350 Carburettor

[simon.holyfield]

Simes
Both this 928 and the 926 are 'premier' concentrics that have the separate pilot jet (screwed in opposite the pilot air screw).
The 'vanilla' concentric just has a pilot drilling (which is just about impossible to clean out properly, unless you drill and thread an access hole opposite the air screw). However, there is also a tapped hole for the pilot system in the top of the float chamber - when the concentrics first came out there was a jet available to screw into that (I've got several) but Amal stopped specifying the fitting of that jet after a while (but they carried on putting a thread in the hole as if something should be there!)

SG

Thanks Simon, I think I must have a blockage there as it has suddenly become more difficult to start and is spitting back. Mine has the threaded hole but no pilot jet - I thought there was a way of removing that fixed pilot jet, or drilling it out?

[Simon.Gardiner]

There are several You-tube vids on drilling out the passages in the carb body. I think there might be a bit of overkill in them - they all seem to involve getting rid of the 'jet' (by pressing it out or drilling it out - yes there are ways!) but it seems to me that just getting access to all the passages so you could properly clean them out would be enough. (The pilot system is quite involved and I had to work pretty hard to get my head around which holes do what, and which holes you can't properly see without a torch and a magnifying glass!)
A couple of vids here (fight your way through the personal story stuff):
https://www.youtube.com/watch?v=hLm7Bia2bCg
https://www.youtube.com/watch?v=j4GMTbJfoIE
This one converts the carb to have 'premier' type pilot jet (2BA is your friend!)
https://www.youtube.com/watch?v=aKthb0Svwaw

I assume the Wassell concentric is the same as the vanilla Amal in that there's no access to half of the pilot system - so to drag this back towards 'on topic' if you're thinking about getting a concentric type there is some benefit in getting a 'premier'.

(And, of course, my previous refs to 926 should be 626 - although that doesn't make any difference to the pilot jet arrangement.)


SG
:

[david.anderson]

The pilot jet in a concentric will just clog with the gum formed by petrol if left unused for a while. It is .017” dia and it can generally be cleared with a piano wire of less than .017”. Alternately try a no 79 drill worked with fingers only and then go to a no 78 which is .017” (equivalent to a no 25 pilot jet). The hardest bit is actually getting the drill or piano wire to start in the hole, generally takes a couple of minutes. The pilot jet threaded hole in the body that hangs into the float bowl is for 2 stroke carbs, not 4 strokes.
David