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- Nov 10, 2012
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I understand but then you need a larger viton or not?A nit having a go with a drill can be successful at enlarging the hole in the needle seat.
Piero
I understand but then you need a larger viton or not?A nit having a go with a drill can be successful at enlarging the hole in the needle seat.
I understand but then you need a larger viton or not?
Piero
That would depend on how much oversize you drill the hole. Drilling the hole is the easy part, you may have to lap in the needle, and that may require machine tools.
Here is the Amal part number and description for the alcohol needle:
622/279 Float Needle Alcohol
The base dia of the cone of the alcohol needle is 5 mm, or about 0.200 inch. One must have sufficient "meat" for the seat, so I would think maximum hole dia. in the seat would be 4 mm or about 0.156 inch.
Slick
Hi Slick,
please, could it help to mount a float bowl extention?.
Thank you.
Piero
A mirror image full carb would be ideal. There were some made, but they are rare.
Slick
A 389/228 is a left side bowl carb for a 650 BSA Lightning and Hornet. It’s also 1-5/32” bore, rather than the stock 1-1/8” bore your bike came with. Not sure how much that affects it. The 689 designates a right side bowl.Hi.
I have found to buy a 389-228, a full right side monoblock.
Do you think is a good idea to replace thechopped with a full.
Sorry is not clear for me understand the fuel line with two full.
Better from bottom banjos like now with full and chopped, or with upper banjos?.
Thank you.
Piero
A 389/228 is a left side bowl carb for a 650 BSA Lightning and Hornet. It’s also 1-5/32” bore, rather than the stock 1-1/8” bore your bike came with. Not sure how much that affects it. The 689 designates a right side bowl.
Please.
Abiut the air screw setting.
With concentrics i start from 1,5 turns unscrewed from full tight.
What is the start setting with monoblocks?
Thank you.
Piero
Hi.
I have found to buy a 389-228, a full right side monoblock.
Do you think is a good idea to replace thechopped with a full.
Sorry is not clear for me understand the fuel line with two full.
Better from bottom banjos like now with full and chopped, or with upper banjos?.
Thank you.
Piero
It’s definitely a right side, they just labeled it incorrectly. However, a 228 is still a 1-5/32” bore, so you would need the same bore size for the left side.is this:
<https://www.brammotoren.nl/a-52124470/carburateur-amal/amal-389-228/>
https://www.brammotoren.nl/a-52124470/carburateur-amal/amal-389-228/
seems to me to be a right side float bowl
Hi.It’s definitely a right side, they just labeled it incorrectly. However, a 228 is still a 1-5/32” bore, so you would need the same bore size for the left side.
Hi Slick,A mirror image full carb would be ideal. There were some made, but they are rare.
The are two problems with the chopped carb ..... 1) the pilot adjustment screw is nearly unreachable on the left carb, and 2) feeding two carbs from one needle and seat will fuel starve a hot 650 engine, and a warm 750 engine.
I use a needle and seat having a 0.200 inch dia orifice, the typical 0.125 inch dia will starve the engine at high revs.
Slick
Hi Slick,
i have just bought the 622/279 viton.
I will rebore the seat orifice to 0.200.
Is 0.156 inch 4 mm?
Thank you.
Piero
I will use the chopped carb.0.156 is 4 mm.
If you will have two full carbs, it is not necessary to bore the seat orifice. Use the standard 0.125 inch orifice on EACH carb's needle seat. A 0.125 orifice will deliver all the fuel ONE carb can use, but not TWO carbs when using a chopped carb.
If you bore the orifice to 0.200, what will you use for a needle? The Amal alcohol needle is 0.200 at the base ..... It will fall thru the 0.200 orifice!
Slick
I will use the chopped carb.
I will rebore the seat to 0.156 inch:4 mm, that is good
With alcolic vitin?
Ciao
Piero
That will work with alcohol needle. Will not work with standard viton needle.
View attachment 13544
(L) Standard Viton (R) Alcohol Needle
If you study the data in the link <https://www.accessnorton.com/NortonCommando/flow-measurements-on-ewarts-fuel-tap.21225/>
you will find a linear relationship between fuel flow and orifice size. From this data, I estimate increasing the orifice from 0.125 to 0.156 will result in 10% greater fuel flow. Is it worth the trouble?
Slick
Edit: If you change bore in orifice, it will raise fuel level. You will have to adjust level by changing shims under seat.
View attachment 13545
For comparison: My 0.200 orifice needle (left) compared to standard viton (right)