MKIIA 850 carb needle: bean can vs peashooter

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NortonMKIIA850 said:
p.s. If dynodave's watching, I heard tell over at the NOC forum that Andover Norton are testing a set of balanced pipes specifically for the MKIIA, if so and the planets align that is something that I'd certainly try one day!
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As I check into this thread on occasion looking for something relevant...
Is it remotely possible the MKIIA did NOT come originally with balanced pipes???? I have no way to know. Does AN doing this testing actually prove the MKIIA did NOT come with balance pipes??? Did the MKIIA come with different carbs???
first: I do not have a MKIIA parts book so my research is limited.
The things I am looking for are if the pipes are the same.... upswept or low interstate. peashooter, interstate, or black caps.
Air box front cover: simple flat or with internal snorkle or black plastic MKIII style..
Any possible explainable difference due to RH4 VS RH10, if any.

I only worked on 1 850A a long time ago and don't remember it it was a 73 or 74.
Currently I default to the cutaway spray tube as being for the balance pipes and jetting changes are for the other applied devices.
Without dyno work and the MKIIA manual I have no way to back it up or advance my opinion. :mrgreen:
 
seattle##gs said:
I have a pair of MK2 amals from a 1979 Triumph. They were absolute pigs and responded to NOTHING until I completely blocked off all passages leading to and from the enriching circuit.
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MkIIs are notorious for having hardened enricher seat seals. They are easy enough to replace, which usually cures the problem you found.
 
dynodave said:
Is it remotely possible the MKIIA did NOT come originally with balanced pipes????
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Not really, as all standard 850s supposedly had balanced pipes.
http://www.classicbike.biz/Norton/Broch ... LineUp.pdf

dynodave said:
Does AN doing this testing actually prove the MKIIA did NOT come with balance pipes???
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I'm not sure what AN can be testing as, once again, all standard 850 'A's had the balanced system, with black caps.

http://www.etmoteur.fr/images/norton_co ... page_3.jpg

dynodave said:
Did the MKIIA come with different carbs???
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Different, to what? If you mean were the Mk2a carb specification/carb numbers different to 850 Mk2 then yes, but it was only the main jet size.

dynodave said:
first: I do not have a MKIIA parts book so my research is limited.
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But you do have access to one: https://issuu.com/sealycycleservice/doc ... 2a_06-5988
Note that the exploded drawings included in that document are from the 1973 parts book as the Mk2/2A supplement is not illistrated.

dynodave said:
The things I am looking for are if the pipes are the same.... upswept or low interstate. peashooter, interstate, or black caps.
Air box front cover: simple flat or with internal snorkle or black plastic MKIII style..
Any possible explainable difference due to RH4 VS RH10, if any.
Click to expand...

Both 850 Mk1A and 2A had (low noise emission) blackcaps and the black plastic airbox as the 'A's were the low noise emission models.
 
Les
Thanks for the link to the MKIIA IPL


dynodave wrote:
Did the MKIIA come with different carbs???

For me different is...is it the only 850 without original cut away spray tube?

Thanks you answer that

So they all have balance pipes and all have cut away spray tube. How much is that a coincidence or is it by design?
 
dynodave said:
Did the MKIIA come with different carbs???

For me different is...is it the only 850 without original cut away spray tube?
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All 850 carbs except perhaps for a few very early ones that left the factory before the change was implemented (see 'Bob Riley's second letter) had the 929/107 stepped spray tubes and 928/104 4-ID ring needles.
 
The illustrated Mk1A supplement (link, below) can be used for reference where the Mk2A is concerned but not all Mk1A parts are the same as Mk2A so 1A part numbers should be checked against those in the 2/2A supplement.

MKIIA 850 carb needle: bean can vs peashooter
 
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I have a copy of Norton Motorcycles Parts List Covering "850" Models After Engine Number 307311, which notes on the cover that it is 'complete for the MK2 and MK2A machines.' It's not illustrated, the pages being both punched and perforated, the latter for pulling out and inserting in existing parts books. In Group 11, it distinguishes MK2A carbs from others and gives them part numbers 065749 for the left and 065750 for the right. In Group 23, under 'Exhaust system MK2A model', it lists 065257 as the left-hand exhaust pipe, and 065256 for the right. At Andover Norton, those last part numbers come up as for the MK3, although they're unavailable and there are no photos. Anyway I assume this means they're the upswept type, as on my MK2A? And they're definitely going to be balanced pipes. Two silencers are listed there for the MK2A, 064170 and 064148: at Andover Norton the first number comes up as the 'black cap'/bean can silencer, and the second number redirects back to the first. Maybe Norton's list has a left and a right? Seems unlikely but maybe. The airbox on my MK2A has the same plastic shell as the MK3, but Andover Norton tell me the fittings are very different, so they're not interchangeable, despite appearances. HTH
 
Looking around also.
Surprised to find the 73 MKIA shows the bean can (black cap) muffler on the low level I/S balanced pipes?

And the 74 MKIIA with the same low level balanced pipes but Interstate mufflers?

After reading Bob Rileys letter again, the stepped spray tube makes even more sense (now) for both the mutes AND balance pipes. :mrgreen:
 
My Norton service manual, published prior to the Mark III, shows peashooters, original style airbox and crossover pipes for all 850s. The manual covers all Commandos through 1974 and does not show bean cans/black airbox in any application thru the 1974 model. Based on the service manual, the bean cans/black airbox/smaller diameter main jets came with the '75.

FWIW, Ads for the pre '75 850 Commando shows the peashooters, original airbox, and the crossover. http://www.reproductiondecals.com/image ... 850_74.jpg
 
Yes, I've noticed that in manuals and ads too, but I'd expect the parts list to be the final arbiter here, after all these years? Not forgetting that the bikes actually leaving the factory might've varied any old how ...
 
In Group 11, it distinguishes MK2A carbs from others and gives them part numbers 065749 for the left and 065750 for the right.
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The part number being different is is to reflect the smaller main jet and one notch different needle setting, the stamps on the side of the carb body would also be different as they are the Amal build identifiers for the make up of the carb for the MK2A, these being 31 and 32 for the 2 sides.
 
dynodave said:
Surprised to find the 73 MKIA shows the bean can muffler on the low level I/S balanced pipes?
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I think you are being fooled by the drawing. The Mk1A pipes (so all A models) are 064202 & 064203 with 064170 black caps (and black cap mounting plates).

The 850 Mk1 Interstate/Interpol pipes were 063999 & 064000 and 063130 'Muffler'.

dynodave said:
And the 74 MKIIA with the same low level balanced pipes but Interstate mufflers?
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That's Mk2 Interstate/Interpol. = 065467 & 065466 with 064610 'Mufflers'.

Mk2A pipes (so all 'A' models) are 065256 & 065257 with the 064170 black cap 'Silencer'.


MexicoMike said:
My Norton service manual, published prior to the Mark III, shows peashooters, original style airbox and crossover pipes for all 850s. The manual covers all Commandos through 1974 and does not show bean cans/black airbox in any application thru the 1974 model.
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The factory manual would have been published before the 'A' models were introduced (in late '73).

http://www.classicbike.biz/Norton/Repai ... mmando.pdf
"European type MK1A variations covered in a separate supplement."
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....Which, as far as I'm aware, was never published.


There wasn't a '74 version manual, so your manual does not actually cover the '74 models, also the 'A' models were initially made for the European market as the US market got the Mk2 although some Mk2A models were sold in the US in late '74 so the Mk3 definitely wasn't the first model to have the black caps and plastic airbox even in the US, Edit: '316170' supposedly being the first US Mk2A.
 
By the way, I mentioned rumours of Andover Norton testing pipes for the MK2A – that's just what I heard, but it might be worth pointing out here that the MK2A pipes would tuck in tighter than for the MK3 at least on the drive side, as the MK2A has the slimmer, pre-MK3 primary chaincase and no electric starter ... I've no idea why they might be different to earlier 850 pipes, maybe they're not and they just happen to be getting tested on a MK2A, although I seem to recall mine has the RH10 head if that makes any difference re exhaust port fittings? FWIW, with unbalanced pipes, mine has the plain old squashable steel ring between pipe and head: https://andover-norton.co.uk/en/shop-de ... 3-nmt2166-
 
NortonMKIIA850 said:
In Group 11, it distinguishes MK2A carbs from others and gives them part numbers 065749 for the left and 065750 for the right.
Click to expand...

Yes, the Mk2A carbs had 220 main jets so they had different Norton part (and Amal build) numbers to Mk1/Mk2 carbs (260 mains) and Mk1A (230 mains).


NortonMKIIA850 said:
In Group 23, under 'Exhaust system MK2A model', it lists 065257 as the left-hand exhaust pipe, and 065256 for the right. At Andover Norton, those last part numbers come up as for the MK3, although they're unavailable and there are no photos. Anyway I assume this means they're the upswept type, as on my MK2A?
Click to expand...

Yes, unfortunately, AN is still playing catch up where the Mk2/2A parts are concerned, not that long ago there were hardly any 2/2A parts listed at all.



NortonMKIIA850 said:
The airbox on my MK2A has the same plastic shell as the MK3, but Andover Norton tell me the fittings are very different, so they're not interchangeable, despite appearances.
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Correct, the plastic shell is the same for Mk1A Mk2A and Mk3 but the fittings are different and breather pipe holes are in different positions.

_________________________

Edit: There is an error on the AN Mk2A exhaust page.....
https://andover-norton.co.uk/en/shop-dr ... nsmission#

....the brackets marked '4' and '5' are not only drawn upside down but are part 06.4150.......
https://andover-norton.co.uk/en/shop-details/16275

....as they are the standard black cap brackets, not the low-level Mk2A Interpol black cap pannier brackets 06.4649 and 06.4650 shown in the AN list view of that page.

The Mk2/2A supplement also has an error on that page, as it lists 064150 (standard bracket) as the Mk2A low-level pannier bracket(2) which it can't be, as the low-level black cap brackets are handed.
 
Good to get the thumbs up for all that, thanks! Just been for another evening blast, man oh man this bike's great as it is! :D

Edit: I've always been wary of Andover Norton's parts listing for the MK2A. Presumably all the drawings at their online shop are lifted from the illustrated Norton factory parts books?
 
How can you rely on factory settings for carb jetting, when the fuel varies depending on location ? Also the weather conditions vary according to geography. The main area to get right is the needles and needle jets. The main jets are not a problem as long as they are too rich. A change of exhaust system will always create the need to change jetting.
 
Well, this being a daily rider (when I get the chance), on public roads, and a bike built in the UK and ridden in the UK, where most of the time the weather, atmospheric pressure etc is anyone's guess from day to day and you're rarely *very* far from sea level, plus the fuel's pretty predictable if you stick to the main outlets, I'm quite happy to use factory settings as a starting point. And I have to have *a* starting point. The main jets are already at 260, I said previously that my next tinker in this regard will be needle-related, and at some point I'll play with the Boyer's timing, to see how its constant advance beyond 3,000rpm matches up with higher revs. The bike's a joy as it is, it's just like I said early in this thread, in so many words, if there's a bit more just waiting to be found then I'd like to find it. All suggestions gratefully received, cheers!
 
The manufacturers' specs are always a good starting point, but to my mind that is all they are. The first thing I do when I obtain or build any bike, is work through its tuning. Especially if they have been in the hands of kids. None of it is a difficult task. Start with the ignition timing and once you have established that is correct, don't move it - tune the carbs against it. Unless you are using, methanol fuel, the manufacturers' recommended ignition timing is usually OK, if it moves while you are tuning the carbs, you can get the same symptoms as changing the jetting. What happens in the combustion chamber relies on a balance between ignition timing, comp. ratio and fuel mixture. Always fit a hotter plug if you are tuning for racing, then fit the cold ones when you actually race. That way the plug readings on the hotter plugs will keep you safe when setting the main jets.
 
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