Author Topic: b40 amal carb  (Read 157 times)

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Greenfield

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b40 amal carb
« on: 01 October, 2017, 09:40:27 »
Checking over my recent b40 (1963) purchase I notice that the carb is an amal 376/231. According to Ratio it should be 376/253. I've managed to start it but its as rough as hell. Can anybody suggest whether this carb will work or do I need to change it. I don't want to start tinkering with settings if its a no goer. Thanks in anticipation.

JulianS

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Re: b40 amal carb
« Reply #1 on: 01 October, 2017, 10:12:20 »
The 376/231 is a 1 inch bore carb (376/253 1 1/16 bore) originally fitted to a Francis Barnett Falcon 87 200cc 2 stroke. The 2 stroke carbs usually have a different spray tube to the 4 stroke ones - look through the bore you see a brass tube protruding rom below. 4 stroke usually cut straight across the top and 2 stroke usually cut at an angle.

If yours is like that it may explain rough running.

Greenfield

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Re: b40 amal carb
« Reply #2 on: 01 October, 2017, 13:39:25 »
Having removed the carb, lifting off the cap with throttle slide, there is a brass tube poking out of the jet block into which the needle goes. this brass tube is flat on top. Is the difference between the carb I have and what should be, a matter of internal parts which can be changed, or do I have to replace the entire unit?

JulianS

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Re: b40 amal carb
« Reply #3 on: 01 October, 2017, 13:50:05 »
If carb is good condition - especially fit of slide in body- with the right jets and slide you will probably be able to adjust it to deal with the smaller bore.

Greenfield

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Re: b40 amal carb
« Reply #4 on: 01 October, 2017, 16:09:45 »
Many thanks for that. I now have a pile of bits on the bench, and looking at the parts I appear to have a mix of carb parts. Surprise surprise!
 Do you know how to tell the difference between a 1" and 1 1/16" choke carb? ...and yes the throttle slide is worn.

JulianS

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Re: b40 amal carb
« Reply #5 on: 01 October, 2017, 16:45:32 »
Just measure the bore - same basic 376 body came with different choke sizes.

Greenfield

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Re: b40 amal carb
« Reply #6 on: 02 October, 2017, 09:19:31 »
Yes 1". There seems to be a separate part, stamped '2' on mine possibly pressed into the body, which would make sense if they're producing a range of choke sizes. Someone may have tried to remove this in the past. I think my best bet is to start from scratch with a new carb, rather than refurbing the current one which will never perform as designed. Thanks again for your help.