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MKIIA 850 carb needle: bean can vs peashooter

Classic Norton Commando Motorcycles.

Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Wed Aug 09, 2017 3:14 am

NortonMKIIA850 wrote:Amal says that the needle jet number indicates the flow rate: 'The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head', at http://amalcarb.co.uk/mk-i-concentric-s ... e-106.html – what to believe? Or is this some sort of cosmic coincidence?!


It has the same caption (below) for all their jets.
All genuine AMAL jets are calibrated to a flow rate. The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head. Beware of imitations as they are just drilled to a size. All our jets are branded and packaged with the official AMAL logo.


It doesn't specifically state "needle jet number", so for needle jets it has to be wrong and is just an error in the wording.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Wed Aug 09, 2017 3:44 am

So John Healy's right then – thanks L.A.B.!
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby acotrel » Wed Aug 09, 2017 11:07 am

Amal needle jets are numbered in accordance with their internal diameter in thousandths of an inch. A 107 needle jet has an ID of 0.107 inch. Main jets are numbered according to their flow rating. You can make your own needle jets on a lathe using brass hex, a 0BA die nut and number drills. Making main jets is more difficult. You really need flow meters and reamers.
As long as you have the two needle jets with close to the same internal diameter, moving the needles up and down gives adjustment, so the actual size is not critical. The important thing is that when you lower the needles in the carbs, you should be able to make the engine cough. If you cannot get it to do that, the needle jets are too large and the motor might be sluggish without you really being aware of it. It really only matters if you are racing your bike. The needle position for best performance is just slightly on the rich side of the cough. If you do that to a road bike, it will probably become more weather sensitive.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby acotrel » Wed Aug 09, 2017 11:22 am

One thing I have not pursued with my own bike is changing the needles to see it I can gain more go as I wind the throttle on. I'm using 6D Mikuni needles in a 0.117 inch needle jet with methanol fuel and it seems to work extremely well. The other common Mikuni needle which will work in a 34mm Mk2 Amal is the 6F, which is richer. I can speculate what that needle might do to the performance, but you never know until you try it. Jetting for methanol is the same as jetting for petrol except the jets are bigger, so jetting for petrol is much more critical. The slightest bit too rich and you go backwards. I don't use Amal methanol needles - they are ridiculous.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Wed Aug 09, 2017 11:22 am

All good stuff, thanks acotrel!
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby acotrel » Wed Aug 09, 2017 11:28 am

Look ! - If I can help anyone with a Commando-based bike go faster, I am happy. There are not enough of us. When I built the Seeley 850, I never believed in it - now I think it is really great. I've never previously used a motor which is so responsive to tuning. It absolutely loves methanol. What I have done with it, I have done with other motors, but it has never worked so well.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby Time Warp » Thu Aug 10, 2017 8:04 am

L.A.B. wrote: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.


Which makes the history of my 1974 US sourced Mk2A (311032) with a build plate dated December 1973 either an oddity or imported from the UK at a later date.
Perhaps I need to get a history check if it is available.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Thu Aug 10, 2017 8:25 am

Time Warp wrote:
L.A.B. wrote: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.


Which makes the history of my 1974 US sourced Mk2A (311032) with a build plate dated December 1973 either an oddity or imported from the UK at a later date.
Perhaps I need to get a history check if it is available.


Well, you could try the VMCC or UK NOC.
http://www.vmcc.net/aboutus/library/FactoryRecords.aspx

AN doesn't have records for that period.
https://andover-norton.co.uk/en/factory-records/
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby Onder » Thu Aug 10, 2017 9:00 am

Makes me wonder, no idea what was originally on the bike, stamped Feb 74.
Came with datebox rear plate, no other airbox parts, connected headers but no
silencers. Tossed by the previous owner.
So I guess it was a Mk2.

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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby kommando » Thu Aug 10, 2017 11:03 am

Check the battery tray, MK2 battery long side front to back on the bike, MK2A battery long side across the bike.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Thu Aug 10, 2017 12:27 pm

A rather more interesting update. I fitted the 4-ring needles today, and there's definitely more go! Not a huge amount, but enough for me to feel it was worth it. I've now checked everything in the carbs, and, apart from the new 4-ring needles, they both have stepped spray tubes, .106 needle jets and new 260 main jets. Great. I haven't put in new .106 needle jets because it didn't occur to me to order them in time for the most recent delivery. I may add them to a future order if I remain power-curious. But the bike now pulls nicely at 80mph, which is quite fast enough for me (besides being illegal on public roads, ahem) given the standard riding position and standard European handlebars. At some point I might risk trying for the ton, see what happens.

One other thing I did today, which might've muddied the waters a bit, is to check the fuel levels using a spigoted plug in the bottom of the float bowl and a length of clear hose (https://andover-norton.co.uk/en/shop-details/20569). I'd checked both float heights recently while cleaning the carbs after the 12-year lay-up, and they were spot on – but the clear hose told a completely different story! Fuel levels in both carbs were way too low, by about 4mm/0.157"! So I raised them. Whatever difference the 4-ring needles made, I guess raising the fuel levels by about that much ought to have made a difference too. One curious thing, the fuel level in the right carb is now at about the minimum of what I understand is the acceptable range – i.e. 0.24" below the top of the float bowl – but the float valve seat is as far down as it'll go. Maybe I need stay-up floats, if I get those I wonder if I'll have to set the fuel levels again from scratch!

Thanks for all the thoughts and support people, as far as my bike's performance goes I'm a happy camper right now! :D
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Thu Aug 10, 2017 1:40 pm

NortonMKIIA850 wrote:I'd checked both float heights recently while cleaning the carbs after the 12-year lay-up, and they were spot on – but the clear hose told a completely different story! Fuel levels in both carbs were way too low, by about 4mm/0.157"!

One curious thing, the fuel level in the right carb is now at about the minimum of what I understand is the acceptable range – i.e. 0.24" below the top of the float bowl – but the float valve seat is as far down as it'll go.


It's not that curious if the float needles the old Viton-tipped brass type.

http://amalcarb.co.uk/optimising-mark-1 ... uel-levels
Needle Valve

If your float chamber is fitted with a brass needle valve, you may find the valve sealing under its own weight, before the float has risen far enough to press it shut. Symptoms of this problem can be that the carburetter takes a long time to tickle, hesitates on pickup and does not idle reliably. A Viton tipped aluminium needle valve is now available that overcomes this problem. It is now fitted as standard equipment to all new Mark 1 Concentric carburetters.



NortonMKIIA850 wrote:Maybe I need stay-up floats, if I get those I wonder if I'll have to set the fuel levels again from scratch!


The StayUp floats aren't likely to make any appreciable difference to the fuel levels but the alloy float needles probably will, and they are an improvement in my opinion.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Thu Aug 10, 2017 2:07 pm

Right, of course! Thanks L.A.B., I had become aware of the aluminium float needles at some point, and then forgotten them – I have the brass ones, so an order to Amal is due! I'll get new .106 needle jets while I'm at it. Only, unless I'm being dense, which is perfectly possible, I don't see the aluminium items for sale separately at Amal's online shop, only as part of a stay-up float kit – am I missing something? Maybe I ought to take the plunge with the stay-up floats anyway. Thanks again for all the help!
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Thu Aug 10, 2017 2:23 pm

NortonMKIIA850 wrote:I don't see the aluminium items for sale separately at Amal's online shop, only as part of a stay-up float kit – am I missing something?




622/197AL

http://amalcarb.co.uk/light-weight-alum ... n-tip.html

"Availability: Out of stock" :roll:
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby acotrel » Thu Aug 10, 2017 2:42 pm

When I am tuning a bike, I always set two things first - float levels and ignition timing, then jet to them as fixed settings. As I have said previously - with petrol, half a thou of an inch wear in the needle jet is the difference between flying and sluggish. If the ignition timing changes, the symptoms can be the same as a change to the jetting.
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