1964 G15 monoblock carbs

pierodn said:
I understand but then you need a larger viton or not?
Piero
Click to expand...

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
 
texasSlick said:
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
Click to expand...

Hi Slick,
please, could it help to mount a float bowl extention?.
Thank you.
Piero
 
pierodn said:
Hi Slick,
please, could it help to mount a float bowl extention?.
Thank you.
Piero
Click to expand...

No. An extension does not prevent fuel starvation, it merely delays the onset of fuel starvation for a few seconds.

Slick
 
texasSlick said:
A mirror image full carb would be ideal. There were some made, but they are rare.



Slick
Click to expand...

How rare? I picked up a matched set of 389/236, 689/236 from Ebay last year. I have them all ready to drop off at Andy’s at Lund Machine for some sleeves.
 
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
 
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
 
pierodn said:
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
Click to expand...
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.
 
pierodn said:
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
Click to expand...

Concentric and Monoblocs are the same.

pierodn said:
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
Click to expand...

To replace with a full is a matter of choice, except if your bike is being fuel starved at high power. If fuel starved, then it would be a good idea.

With two full carbs, the bottom banjos should be retained to balance fuel level in both carbs. The two full carbs should each have a top banjo to the fuel needle seat.

Fuel starvation with a chopped carb occurs because both carbs receive fuel thru one needle and seat. With two full carbs, each carb has its own needle and seat. It is the needle and seat that principally limits fuel flow.

Slick
 
Paul W. said:
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.
Click to expand...
Hi.
Can i rebore the 1 1/8 to 1 5/32?
The difference is 0,08 in mm.
Thank you.
Piero
 
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texasSlick said:
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
Click to expand...
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
 
Last edited:
pierodn said:
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
Click to expand...

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
 
texasSlick said:
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
Click to expand...
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
 
pierodn said:
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
Click to expand...

That will work with alcohol needle. Will not work with standard viton needle.

1964 G15 monoblock carbs

(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.

1964 G15 monoblock carbs

For comparison: My 0.200 orifice needle (left) compared to standard viton (right)
 
Last edited:
texasSlick said:
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)
Click to expand...

Hi Slick,
you say : " You will have to adjust level by changing shims under seat.".
What shim?, thin, thick?
Please, let me understand what i must do.
A question more, the float is adjustable like the concentric?.
Thank you.
Piero
 
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