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needle jet question

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Hi to all , quick question on needle jet sizes on a pair of standard 932 carbs , they have the cut away spray tube , andover norton only list the 106 needle jet but Haynes manual says 104 if its the cut away tube . It is currenly fitted with a 106 and needle was fitted on middle groove which should explain why it has been running sooty black , wondering how much difference the jet itself will make , any opinions appreciated , thanks

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First, don't take the Haynes manual for gospel — I haven't checked, but memory suggests that carb settings are one area where Haynes is definitely misleading.

Second, what model Commando do you have?

Third, do you have any symptoms apart from the sooty plugs?

Fourth, needle/jet issues can make a big difference. When I got my Fastback it was almost unrideable at moderate throttle openings due to unstable carburetion. Investigation revealed that the needles (and hence inevitably the jets) were completely shagged, evidently thanks to the rattly slides.

New hard anodised slides, together with new needles and jets, put everything right.

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"Needle jet" and cutaway "spray tube" are entirely different pieces ?

needle jet has a size and spray tube has a part #

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The first thing you look at is there any wear on needled jet, and needle. It would seem obvious to me that a 104 is smaller than a 106. SO...if it is running rich AND you have new needles and jets AND the needle is in its lowest position then you might need a 104? But I am open to correction. I did also think that Spray Tubes were MKIII only. BUT again they do work in other engines (although I do not know the long term effect/result)

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Spray tube change was most if not all 850's , a 104 needle jet is too small, if it works then its masking other issues.

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Hi , thanks for replies , bike is a 1974 Mk2 ( actually made december 73 on headstock plate ), recently imported from america , probably not run for 30 years so carbs were badly gunged up . Have replaced all jets and needles including 106 needle jets . The spray tube is the 928/107 cut away version that andover state is for MK2A and which haynes is saying goes with a 104 needle jet . With years of experience using haynes manuals i am well aware of occasional dodgy information hence why i am asking on here . The slides seem in reasonable condition so for the moment it's a ' see how it goes ' . Would like to get it running well before bike gets stripped for full rebuild , just wondered if fitting the 104's was common practice

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Haynes are wrong, the part number for the stepped spray tube is 928/104, mk2a needle jet is 106 as per riders handbook and as on my mk2a carbs. They have mixed up a part number with a jet size, hence the use of Haynes manuals as doorstops.

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The stepped spray tube is Amal 928/107 and the needle is 928/104 - the latter has 4 rings so please make sure you use the correct needle and not one with 2 rings, which is for the unstepped tube.

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Mystery solved , thanks Alan , Haynes are quoting needle part number for the needle jet and i am happy that all the parts i have fitted are correct . Now waiting for non sinking adjustable floats as float level is low on one side and running hot , other side a bit low too , maybe thats why its not happy when i take the choke off

 

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