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D10 Concentric Carb Overhaul
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Sponge
Lancashire (A chip shop somewhere near Preston)
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January 13, 2021 - 9:59 am
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I am just overhauling the 626 Concentric on my D10A and have taken delivery of an AMAL major repair kit. Having stripped the carb down for cleaning I laid out all the original 1967 parts and went through the comparison exercise under my magnifying glass. 

It is all fine except for the needle jet. The original works fitted needle jet has two tiny holes on either side wheras the new one does not. 

I had a look in the BSA workshop manual and have noted that these two holes as referenced as being there in order to provide a pool of fuel in a well around the jet in order to be available for 'snap accelleration'.  

This sounds good ...

So I have left the old jet in place and have re-placed all the rest. 

I was therefore wondering if any other Bantam owners have noted these holes and what they think about them ? Do they make a difference ?

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Isbfan
Mickleover, Derby
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January 13, 2021 - 1:57 pm
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I was told those additional holes were for four stroke engines. Worth calling Burlens for confirmation though

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Alan.Moore
Leicestershire
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January 13, 2021 - 5:08 pm
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Les

Have a look at this page on the Burlen website ** Please log in to view **

Looking at that page it shows that the 4 stroke type needle jet (with the two bleed holes) is matched to a 4 stroke needle and a 4 stroke needle jet holder...so its possible that if your rebuild kit has a 2 stroke needle jet (no holes) it also has a 2 stroke needle which will not match your old 4 stroke jet. The pics on the burlen site should tell you what you have. (also note the different thread lengths on the two types of jet)

The 4 stroke needle jet (622/122) was the factory fitted jet on a B175 concentric. The 2 stroke jet 622/079 was factory fitted to D10 and D14.

I don't know why the D10 and D14 factory manuals both state the needle jets on those models have the bleed holes...according to the parts books it is clear that they don't.

As to whether the 4 stroke type jet/needle makes a noticeable difference... BSA decided to change to these parts on the B175 so they must have thought it was necessary on that model. 

Cheers

Alan

1939 Ariel VH, 1942 Ariel WNG, 1951 Triumph 6T Thunderbird, 1970 BSA Bantam B175, 1980 Honda CB250N, 1986 Yamaha SRX600

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Sponge
Lancashire (A chip shop somewhere near Preston)
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January 13, 2021 - 6:39 pm
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Alan.Moore said
Les

Have a look at this page on the Burlen website ** Please log in to view **

Looking at that page it shows that the 4 stroke type needle jet (with the two bleed holes) is matched to a 4 stroke needle and a 4 stroke needle jet holder...so its possible that if your rebuild kit has a 2 stroke needle jet (no holes) it also has a 2 stroke needle which will not match your old 4 stroke jet. The pics on the burlen site should tell you what you have. (also note the different thread lengths on the two types of jet)

The 4 stroke needle jet (622/122) was the factory fitted jet on a B175 concentric. The 2 stroke jet 622/079 was factory fitted to D10 and D14.

I don't know why the D10 and D14 factory manuals both state the needle jets on those models have the bleed holes...according to the parts books it is clear that they don't.

As to whether the 4 stroke type jet/needle makes a noticeable difference... BSA decided to change to these parts on the B175 so they must have thought it was necessary on that model. 

Cheers

Alan  

Alan and Isb, many thanks for the responses and I am glad I asked. Having seen your thoughts and guidance my intention is to swap out the needle jet with the holes and replace it with the one in the 'major repair kit' ...then see how she runs. 

Being pretty sure that the 626 on the D10 is original factory fitment I do wonder if it ever ran right ..it was retired after about 3 years and 6000 miles with a seized piston in the bore. The nice old bloke I bought the bike from explained that Fowlers of Bristol said it would cost just as much to fix it as the cost of a 2nd hand D10, they didn't even offer him a part ex trade in. So he bought the 3 year old D10 and stored the original bike in his shed for 48 years......until I bought it in early 2019.  I am doing a mechanical only overhaul, only replacing those parts that are busted and cannot be repaired. 

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Alan.Moore
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January 13, 2021 - 6:55 pm
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Les

Bear in mind the 4 stroke needle jet 'holder' is also different (it is longer than the 2 stroke one) so double check which one is fitted in your carb.

needle-jets.JPG

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1939 Ariel VH, 1942 Ariel WNG, 1951 Triumph 6T Thunderbird, 1970 BSA Bantam B175, 1980 Honda CB250N, 1986 Yamaha SRX600

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