Amal 93 carburetor jet sizes

rhino64

rhino64

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What would be a good starting point for the carburetor jetting for a P11 with a stock camshaft and .040" oversized pistons?
 
The obvious answer is stock jetting, however it depends on which carburetors you are using. The original 1967 concentrics used a different needle and needle jet than the later ones. The original carbs had a needle jet with the orifice (where the needle controls the flow) at the top, no bleed holes, and used with a short needle. The original size was a 107. The later carbs have the orifice at the bottom of the jet with bleed holes (in the hex). That is a more efficient design, and a 106 would be the correct size with the longer three ring needle, just like an early Commando. The main jet was 250, and screw in pilot jet (if you have one) is a
25. Oversize pistons, and slightly more compression won't change things.

Mike B.
 
Mike B said:
The obvious answer is stock jetting, however it depends on which carburetors you are using. The original 1967 concentrics used a different needle and needle jet than the later ones. The original carbs had a needle jet with the orifice (where the needle controls the flow) at the top, no bleed holes, and used with a short needle. The original size was a 107. The later carbs have the orifice at the bottom of the jet with bleed holes (in the hex). That is a more efficient design, and a 106 would be the correct size with the longer three ring needle, just like an early Commando. The main jet was 250, and screw in pilot jet (if you have one) is a
25. Oversize pistons, and slightly more compression won't change things.

Mike B.
Click to expand...

What if mine are a 106 needle jet (no holes) - short needle with 3 grooves?
Can I upgrade to the long needle, 107 needle jet with orifices or should I just leave the original set in? If I stick with original 106 needle seats what should the jetting be?
I do have pilot jets.
 
rhino64 said:
What if mine are a 106 needle jet (no holes) - short needle with 3 grooves?
Click to expand...

The later '4-stroke' needle (622/124) has two identification rings (these are not the clip grooves).


http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
Needle Jets

In 1969 a new needle jet, needle jet holder and needle , designed specifically for 4 stroke carburetters, was introduced to improve low to mid-range performance.

A conversion kit (622/235) is available to update to the new parts.
Click to expand...

http://amalcarb.co.uk/4-stroke-conversion-kit.html
Contains Parts: 622/122-106 622/124 & 622/128
Click to expand...
 
Converting to the later components is the way to go, I did so 27 years ago. No regrets.
Mike B
 
L.A.B. said:
rhino64 said:
What if mine are a 106 needle jet (no holes) - short needle with 3 grooves?
Click to expand...

The later '4-stroke' needle (622/124) has two identification rings (these are not the clip grooves).


http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
Needle Jets

In 1969 a new needle jet, needle jet holder and needle , designed specifically for 4 stroke carburetters, was introduced to improve low to mid-range performance.

A conversion kit (622/235) is available to update to the new parts.
Click to expand...

http://amalcarb.co.uk/4-stroke-conversion-kit.html
Contains Parts: 622/122-106 622/124 & 622/128
Click to expand...
Click to expand...

Thanks L.A.B.
Allot to take in but very helpful! It apears that I have a four stroke carb with a 2 stroke needle. I have ordered the conversion kit from Amal. Once this kit is in place will the 250 Main and 25 idle jets work for the P11?
 
Just like going to college...with every answer I have more questions.
What size slider do you recommend for the P11?
Mine are stamped 2-1/2"
 
rhino64 said:
It apears that I have a four stroke carb with a 2 stroke needle.
Click to expand...

It was after Amal introduced the specific 4-stroke, 2 ring needle, 4-stroke needle jet and jet holder in '69 that the 3 ring needle then became the '2 stroke' needle.
 
My carbs came off of a 67-69 T-20 Bonneville 930/9 - 930/10.
I guess I will go with the conversion and run 250 Main and 25 idle :roll:
We'll see how that goes.
 
rhino64 said:
Just like going to college...with every answer I have more questions.
What size slider do you recommend for the P11?
Mine are stamped 2-1/2"
Click to expand...


The best I can do is give you the original P11 carb spec. from the '63 - '68 parts list;

Throttle valve (slide) = 3.0
Needle, 928/063 (original 3 ring needle)
622/079, 107 Needle jet (original needle jet)
Main jet ("with air filter") = 250
Pilot jet = 25


rhino64 said:
My carbs came off of a 67-69 T-20 Bonneville 930/9 - 930/10.
Click to expand...

According to the parts list, the P11 carbs were 930/7 and 930/8 [Edit] (and which matches the Amal carb numbers for P11). Needle jet is 107 according to Amal's spec. although the 4 stroke conversion kit contains a 106.
http://amalcarb.co.uk/carbspec/carburet ... s/id/5464/
 
Very good L.A.B. I think I will get the 3" slider and the new conversion at 106. Thank you all for your most generous help. Love this forum!!!
 
L.A.B. said:
rhino64 said:
Just like going to college...with every answer I have more questions.
What size slider do you recommend for the P11?
Mine are stamped 2-1/2"
Click to expand...


The best I can do is give you the original P11 carb spec. from the '63 - '68 parts list;

Throttle valve (slide) = 3.0
Needle, 928/063 (original 3 ring needle)
622/079, 107 Needle jet (original needle jet)
Main jet ("with air filter") = 250
Pilot jet = 25


rhino64 said:
My carbs came off of a 67-69 T-20 Bonneville 930/9 - 930/10.
Click to expand...

According to the parts list, the P11 carbs were 930/7 and 930/8 [Edit] (and which matches the Amal carb numbers for P11). Needle jet is 107 according to Amal's spec. although the 4 stroke conversion kit contains a 106.
http://amalcarb.co.uk/carbspec/carburet ... s/id/5464/
Click to expand...

Hi Les,
sorry, but why if Amal says that "Needle 928/063" is for two stroke the P11 setting require it?.
On my P11 carburetors 930/7/8, i use all the carb specs but not the 928/063 throttle needle and use the common 622/124 fitted on all my Commando.
What is the real difference?
Thank you.
Piero
 
pierodn said:
sorry, but why if Amal says that "Needle 928/063" is for two stroke the P11 setting require it?.
Click to expand...

928/063 (3 ring) needle was the 'two stroke' needle ONLY AFTER the introduction of the 4 stroke needle and needle jet in 1969.
Before then, the 928/063 was used for both 2 strokes and 4 strokes.


pierodn said:
On my P11 carburetors 930/7/8, i use all the carb specs but not the 928/063 throttle needle and use the common 622/124 fitted on all my Commando.
Click to expand...


Yes, as the 622/124 (2 ring, 4 stroke) needle when used with the later 4-stroke needle jet and jet holder should perform better than the original P11 carb specification.


http://amalcarb.co.uk/rebuilding-mark-1 ... arburetter
In 1969 a new needle jet, needle jet holder and needle , designed specifically for 4 stroke carburetters, was introduced to improve low to mid-range performance.
Click to expand...

(I believe the 4 stroke needle and jet were actually introduced during 1968. The Amal Concentric Mk1 introduced late '67)
https://www.princeton.edu/ssp/65-cub-da ... itbike.pdf
Pilot jet:
When Concentrics were first fitted in 1968 they were in, what is now called, a two stroke condition. This included the removable pilot jet we see in many after market repair manuals. Low speed problems led to further testing giving us what we now know as the four stroke carb.
It had the pilot jet pressed in the body, the spray tube was modified, a new needle and needle jet design was developed and the main jet holder was lengthened to allow the main jet to be deeper in the bowl.
All British four stroke twins (late 1968) soon came with the new four stroke carb and a "update kit" (Amal # 622/235) was offered for bikes fitted with the early carb.
Click to expand...
 
CanukNortonNut said:
That is a great pdf and should go in our technical sticky. :) if not already.
Click to expand...

Yes, a good idea.
I've added the link to the tech sticky. :wink:
 
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