monoblock B40 queries

[chaz]

right, today was the day, the B40 fired up and run.
apart from a leak at the fuel tank fixed with ptfe, I had a leak from the monoblock carb.

first, the outer cover probably needs a new gasket but the A10 has been on and off many times but always seals. any problem area to look at as the body only has a small face.
secondly, the cut off valve housing, the valve does not cut off with a fibre washer fitted. removed washer and used ptfe now has sealed and cuts off. I note Amal catalogue says "if fitted" on washer description. anyone not using a washer or are there different thicknesses?
thirdly, the throttle stop screw 376/068 screws in but meets a heavy resistance , Ive tried it on another 376 and the same thing. I dont want to break the plain diameter off as Ive already got one like it. Is it a faulty new part or is there an option ? I could do with increasing tickover.

[JulianS]

If your monobloc is an original one which takes the thick O ring then the fibre washer is not fitted, never was- it is only for the newer monoblocs which take the thin concentric O ring. This later version has a recess for the washer.

When fitted to the early carb the tickler plunger stops the float from fully rising and sealing the needle, hence the flooding

The mazac float covers are often distorted after many years of fitting and removing.

[chaz]

thanks Julian, that covers the first questions.

just the throttle stop/tick over screw to sort

[Spaceman]

The throttle stop has a 2BA thread and should screw all the way into the carb without much resistance. If the same problem occurs on 2 separate carbs then the screw sounds to be at fault and has either a damaged thread or is more likely is slightly bent. 

[chaz]

the screw is a new chromed item, the spring that comes in the kit does not start to compress.
Ive ruled out position as the spare carb has not got the slide block screw in so should find its own position. Amal genuine part but not impossible that its oversize. I might make one myself from stainless slightly smaller plain diameter.

[Spaceman]

The thread diameter for 2BA is 0.1850 inch. Normally, the screws are zinc plated but if this one is actually chrome plated then it might well be over size!

[Spaceman]

Just for reference, the collection of old throttle stop screws I've got all measure 0.182 inch. Non have still got their zinc coating left but, by the time you've added a few microns of zinc, it's not going to increase the diameter by anywhere near an extra thou.

[chaz]

Ive now made a new screw out of stainless.
the problem seems to have occured with the plain part of the hole not being true to the 2ba thread in the body. Ive opened up the hole in the spare body and both screws now work correctly. the carb on the bike , Ive slightly opened up the hole which was partially blocked but seems like the 2ba thread isnt as deep as the spare carb is.

as for the leaking chamber, I think its down to the wall thickness, comparing both bodies, the one on the bike has half the wall thickness as the spare one. Ive put some welseal on to try but will be looking for a spare body to clean up and rebuild.