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276 Rapide carb jets

ernie

Well Known and Active Website User
VOC Member
I am rebuilding Rapide carbs from bits I have accumulated over the years.

Here are pictures of 3 different things, I do not know what the part names are but you will recognise them - jet blocks?

They are all stamped 30T on the bottom and 45 on the top, same as the ones fitted on the bike at the moment. What is the difference between them please?
 

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Len Matthews

Well Known and Active Website User
VOC Member
Yes, Ernie they are jet blocks. I don't know what the numbers mean but an Amal speciallist (big ad in Old Bike Mart) should know. The one on the right in picture2 looks suspect; it appears to have been machined for some unexplained reason.
 

ernie

Well Known and Active Website User
VOC Member
No Len, that is a variation I am asking on. I have another one like that. The one on the left seems to be like the one in my current carbs (left and right hand). The other 2 are variations I would like to know more about.
 

Tom Gaynor

Well Known and Active Website User
VOC Member
One of those looks very like the jetblock I replaced in a 276 earlier today. The central hole in the front (the "choke" side, RH pic, LH jet block) aligns with a passage from the "floor" of the venturi upstream of the slide which I think must feed air to the pilot jet when cold-starting. Never seen one with two holes before.
 

vince998

Well Known and Active Website User
VOC Member
Hi Ernie,
Can´t help you with the jet blocks, but judging by your picture, you really need to start wearing a full face lid (if you can find one to fit!!), or try riding a bit slower :D
 

blueshed

New Website User
Non-VOC Member
What you have there is a potted history of Amal Standard Carburetter jet blocks!

Amal used a series of numbers indicating carburetter bore sizes. 45 indicated a 1" bore carburetter and may indicate the choke size of these jet blocks. The 30T is related to the pilot drilling which is most commonly equivalent to a 30cc pilot jet.

The jet blocks for pre-war Type 6 and Type 76 carburetters drew air through four drillings around the circumference of the mixing chamber . The jet block in the centre of the photos is one of these.

In 1939 the four holes were eliminated and and a flat was milled across the top of the jet block with two primary air passages drilled through it. The motivation was the need to ensure proper air filtering - particularly in the Western Desert! At that point the carburetters became Type 276.

This modification was quickly superseded by a further design where a primary air hole was drilled to align with the air intake passage in the carburetter air intake. That's the third one of the set.
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
Rapide's front and rear 276's were fitted with a block numbered 51......a slightly larger choke.

I posted a list of the right Amal specification some time ago....Ernie,I'll send you a copy off list.

Cheers

Vic
 

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