MK II 850 Commando 1974 Amal Carb choice.

Britstuff

Britstuff

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Hi:

I'm thinking about treating my Commando to a pair of new Amal premier carbs. However, there appears to be a couple of different choices. Either PACK 136: main jet 260, slide 3.5 or PACK 138: main jet 200, slide 3. Which one should I get?

I'm currently running a pair of original Amals with some wear, pretty sure the main jets are 260's, not sure about the slides. The carbs are not original to the bike. I believe my engine to be fairly standard, I think the cam is stock, valves are standard size, head does not appear to have been shaved (RH10), 0.040 rebore with flat top pistons. Peashooters without baffles and no exhaust balance pipe. Lucas rita electronic ignition. I live in Vermont and have access to and try to run on Ethanol free 90 octane gas whenever possible. Earlier type air filter. I am pretty sure it is a MK II, not a MKIIa.

Seems to me that the carbs for early 850's with the larger 260 jets would be the ones to go for?

Does anyone know why there was a change for later 1974 bikes. Emissions regulations maybe?

Thank you,

Kind Regards,

James
 
Britstuff said:
Hi:

I'm thinking about treating my Commando to a pair of new Amal premier carbs. However, there appears to be a couple of different choices. Either PACK 136: main jet 260, slide 3.5 or PACK 138: main jet 200, slide 3. Which one should I get?

I'm currently running a pair of original Amals with some wear, pretty sure the main jets are 260's, not sure about the slides. The carbs are not original to the bike. I believe my engine to be fairly standard, I think the cam is stock, valves are standard size, head does not appear to have been shaved (RH10), 0.040 rebore with flat top pistons. Peashooters without baffles and no exhaust balance pipe. Lucas rita electronic ignition. I live in Vermont and have access to and try to run on Ethanol free 90 octane gas whenever possible. Earlier type air filter. I am pretty sure it is a MK II, not a MKIIa.

Seems to me that the carbs for early 850's with the larger 260 jets would be the ones to go for?

Does anyone know why there was a change for later 1974 bikes. Emissions regulations maybe?

Thank you,

Kind Regards,

James
Click to expand...
Contact Greg Marsh…
 
Britstuff said:
Hi:

I'm thinking about treating my Commando to a pair of new Amal premier carbs. However, there appears to be a couple of different choices. Either PACK 136: main jet 260, slide 3.5 or PACK 138: main jet 200, slide 3. Which one should I get?

I'm currently running a pair of original Amals with some wear, pretty sure the main jets are 260's, not sure about the slides. The carbs are not original to the bike. I believe my engine to be fairly standard, I think the cam is stock, valves are standard size, head does not appear to have been shaved (RH10), 0.040 rebore with flat top pistons. Peashooters without baffles and no exhaust balance pipe. Lucas rita electronic ignition. I live in Vermont and have access to and try to run on Ethanol free 90 octane gas whenever possible. Earlier type air filter. I am pretty sure it is a MK II, not a MKIIa.

Seems to me that the carbs for early 850's with the larger 260 jets would be the ones to go for?

Does anyone know why there was a change for later 1974 bikes. Emissions regulations maybe?

Thank you,

Kind Regards,

James
Click to expand...
The smaller main jets go with the introduction of the Black Cap silencers and a big power reduction. The Black Caps were designed to reduce sound level of the Commando. This was a new requirement in the big California market back then.
Nowadays straight pipe Harleys are OK. Go figure.
260s seem to be ideal with open Peashooters if running mostly at sea level to 2 or 3 thousand feet.
 
Thank you all.... 260's it shall be.

I got my information from this handy reference chart at Andover Norton:

andover-norton.co.uk

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.
andover-norton.co.uk

No disrespect intented to L.A.B, but it seems to suggest that the carbs with the 260 jets are /29 and /30?

I wish the Amal website made the specs a bit easier to find.
 
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I have a 74 RH10 head and New Aluminum Premiers. They have the 260 mains so I would start there. I am using single down tube exhaust per cylinder, with pea shooters. The bike came with the cross over pipe but they all crack at the welds there.:rolleyes:
You save 1.5 lbs of weight by changing from the Zinc pot metal Amals, to the new Premiers. So that is a plus.
FYI. A little tip.... You may have to take the two into one junction apart and separate the two cables from there to the slides to get enough cable distance to loop it through the slide bottom keyhole with the spring in coil bind.
That's what I had to do. They are a little harder to get the cables to pass into the slides due to the re-design of the anodized slides. Maybe your fingers are stronger or the way you position your tongue will help ?🤣
Cheers,
Tom
 
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Britstuff said:
Thank you all.... 260's it shall be.

I got my information from this handy reference chart at Andover Norton:

andover-norton.co.uk

Andover Norton Parts Drawings - Genuine Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.
andover-norton.co.uk

No disrespect intented to L.A.B, but it seems to suggest that the carbs with the 260 jets are /29 and /30?
Click to expand...

Yes, /29 and /30 are 850 Mk1. /35 and /36 should also be 260 (for peashooters) for Mk2 (not 2A) so AN's list is wrong in my opinion.

So what jets/slides are you currently using?
 
Thank you LAB, I am grateful you pointed this out. I will double check before making a purchase.

pretty sure I am running 260 jets, not sure about the slides. It certainly seems like the AN chart has a typo. If the /35 and /36 said 260 main, instead of 200 it would make much more sense.
 
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Detail on my site, generally:

850 carbs are easier than 750 because the only differences are the main jet, needle position, and carb sub-number. I stock all Norton Commando carb versions mainly so those trying to make their bike "correct" will have the "correct" carbs.

The big difference in 750 32mm and 850 32mm carbs is that the 850s all have a special Norton needle and spray bar, and the 850s have a 3-1/2 slide where 750s have 3 slides.

750s have 30mm carbs until the Combat and final 750s. The Combat used 32mm (originally with 220 and later 230 with main jets) as did the "1973" 750s but with different specifications.

It took forever but we convinced AMAL to supply 850 Premier sets with #19 pilot jets. They insist on #17 for 750s. So, I supply #19 for 750s.

If you buy 932/300 and 932/301 (generic) for your 850, they are NOT correct even with the correct jets - wrong needle and wrong spray bar.
 
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A bit of a tangent here but quality control on some jets may not be what you would like. For example
I bought new needle jets (0.106) and jet needles for my sleeved 932s on a MKIII with 2s cam. 3-1/2 slides. The new needles are tight in the new 0.106 jets. Other needles identically marked but showing no wear marks are not tight in the jet. Once warm it runs fine but seems lean as I must run with the choke for several minutes. I'm at 2500 ft. elevation and running a ham can AC and open peashooters, non-ethanol 92 octane premium (at least that's what the pump says).
 
CanukNortonNut said:
I have a 74 RH10 head and New Aluminum Premiers. They have the 260 mains so I would start there. I am using single down tube exhaust per cylinder, with pea shooters. The bike came with the cross over pipe but they all crack at the welds there.:rolleyes:
You save 1.5 lbs of weight by changing from the Zinc pot metal Amals, to the new Premiers. So that is a plus.
FYI. A little tip.... You may have to take the two into one junction apart and separate the two cables from there to the slides to get enough cable distance to loop it through the slide bottom keyhole with the spring in coil bind.
That's what I had to do. They are a little harder to get the cables to pass into the slides due to the re-design of the anodized slides. Maybe your fingers are stronger or the way you position your tongue will help ?🤣
Cheers,
Tom
Click to expand...
Try winding the spring on instead of trying to compress it 👍👍👍
 
I would buy the richest recommended jets and work downwards from there. It isn't a tragedy when you buy a few smaller jets and try them. I am too lousey to buy needle jets for my Mk2 Amals, so I make them out of brass hex, and get much finer adjustment. But I do not make my own main jets, so I spend a dollar. In any case, with main jets, I always err on the rich side. It is safer and does not rob much power. Needle jets are very different if they are even slightly too rich - the motor will be slower, particularly when using petrol. The exhaust system and cam timing affect the jetting, and also the weather. If your motor develops a miss while you are riding, stop and fix it. A miss usually means too lean and you can do engine damage - burn pistons and valves.
If the largest recommended main jet is 260, I would work downwards in a couple of steps of 20 - buy 260, 240, 220. You are unlikely to fit megaphone exhausts. 260 is probably 'one size fits all'.
 
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