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MKIIA 850 carb needle: bean can vs peashooter

Classic Norton Commando Motorcycles.

MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 3:13 am

Hi,

I've owned my MKIIA 850 (Europe) since 1998, and have recently got it out of storage after 12 years. (long story) It has the MKIII-style black plastic airbox, sectioned spray tubes and 4 ID ring needles that you'd expect on a MKIIA, but it was wearing straight-through peashooter silencers when I bought it, instead of the bean cans with which it would have left the factory. While rummaging through old Norton content on my computer yesterday I found a note from 2002 by Frank Forster, who might be on Access Norton...? Whether or not, I hope he doesn't mind me bringing this up. Anyway, he wrote: 'The 4 ID ring needle was made for the restrictive "bean can" mufflers used on the MK III Commando [and the MKIIA], and are correct for that use. For any Commando using mufflers of the "straight through" design, one must use the 2 ID ring, as otherwise there will be a lean spot when you open the throttle to increase from a 70 MPH speed.'

Is this still believed to be the case? If so, I'd better get some 2-ID-ring needles pronto – my Commando has always seemed lacking in power much above 70 mph, and doesn't like pulling much above 85 – 90. Even though I had the engine rebuilt by Norman White many years but only a few thousand miles ago. While I don't want to risk burning valves etc. by running lean at high speed, might this needle issue be behind the apparent drop in power? TIA
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Sun Jul 23, 2017 3:45 am

NortonMKIIA850 wrote:'The 4 ID ring needle was made for the restrictive "bean can" mufflers used on the MK III Commando [and the MKIIA], and are correct for that use. For any Commando using mufflers of the "straight through" design, one must use the 2 ID ring, as otherwise there will be a lean spot when you open the throttle to increase from a 70 MPH speed.'

Is this still believed to be the case?


Thanks to the testimony of Norton tester Bob Rowley (and the parts books) we now know for certain that's not correct, as stepped spray tubes and 4 ID ring needles were, in fact, fitted to (practically) all 850 Commandos regardless of whether they were Mk1, Mk2 (peashooters) or Mk1A, Mk2A, Mk3 (black airbox & black cap/bean cans) models, therefore, 4 ID needles should be used with the stepped spray tubes, alternatively, 2 ID needles and flat topped spray tubes can be used.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 4:05 am

Ok great, thanks for that, it's a relief to be honest! So I'll be keeping those needles and sectioned spray tubes. Now I only have to ponder what I said about my bike appearing to run out of steam at high speed. Maybe the only way to be sure would be a direct comparison with another straight MKIIA. I don't think I've ever managed to get mine over 100 mph. I'm really not a speedfreak and generally observe speed limits (getting older, see...!), it's just nice to have power and know what the bike can do. Cheers!
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby kommando » Sun Jul 23, 2017 4:22 am

My MK2A had peashooters but had the blackbox and ran out of steam over 3/4 throttle, the 230 main jets had been retained and when replaced with 260's (as per the MK2 fitted with peashooters as std) the bike was restored to full power. There is a difference of one slot on the needle position MK2 to MK2A but not checked to see what I did there.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Sun Jul 23, 2017 5:20 am

NortonMKIIA850 wrote:my Commando has always seemed lacking in power much above 70 mph, and doesn't like pulling much above 85 – 90.


That does seem a bit down on power so maybe it needs a good going over?
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 6:40 am

Thanks for that L.A.B., so I'm not the only one thinking it might be a bit down on power. And kommando, for the suggestion that I might up the main jets! I'll see what I can see! Cheers.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby grandpaul » Sun Jul 23, 2017 6:48 am

If the stock configuration has been modified for free breathing, you'll need to step up the mains to get all it's got.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Sun Jul 23, 2017 7:02 am

NortonMKIIA850 wrote:It has the MKIII-style black plastic airbox


Does it still have the rubber venturis fitted to the airbox trumpets by any chance as I believe they may restrict top end power.

https://andover-norton.co.uk/en/shop-de ... ke-venturi

The foam filter element degrades and eventually begins to crumble and the carb connector hoses can split so perhaps worth checking as well as the main jet sizes already mentioned.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 7:10 am

Interesting point, GrandPaul. I remember something 17-odd years ago about the MKIIA inlets (and presumably the MKIII?) being tapered towards the valves, supposedly to improve torque, of which there was and is *plenty*, and the wisdom was to open these tapers up to straight through for more bhp. I had this done all those years ago in search of more bhp, just because the bike seemed to give less than it ought at higher speeds, but I felt it didn't make a difference. So, another reason to up the main jets, it seems. I see these jets are fairly cheap – they'll be the standard ones in there since the carbs were fitted new by me in a previous life – I wonder if it would be safe to go straight to 260 and see, or whether I should try it in steps. L.A.B., apart from the removed tapers in the inlets, intake is all standard MKIIA, so the carb connector hose from the airbox is two of these:

https://andover-norton.co.uk/en/shop-de ... ector-hose

The hoses are only a few weeks old, and the filter was new some years ago, I'll have a look at it.

Cheers.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 7:16 am

Sorry L.A.B., I only just tumbled to what those venturi that you linked to are! I'd never seen them before ... They're not on my bike and never have been, since I bought it! Yet another reason to open up the main jets, I guess ... Cheers!
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby kommando » Sun Jul 23, 2017 7:23 am

Never had those on mine either, do have a pair in a box and they are staying there.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Sun Jul 23, 2017 7:25 am

NortonMKIIA850 wrote:Interesting point, GrandPaul. I remember something 17-odd years ago about the MKIIA inlets (and presumably the MKIII?) being tapered towards the valves, supposedly to improve torque, of which there was and is *plenty*, and the wisdom was to open these tapers up to straight through for more bhp. I had this done all those years ago in search of more bhp, just because the bike seemed to give less than it ought at higher speeds, but I felt it didn't make a difference.


.....And is now considered not to be such a good idea! :wink:
rh4-rh10-cylinder-head-performance-t27073.html

NortonMKIIA850 wrote:I wonder if it would be safe to go straight to 260 and see, or whether I should try it in steps.

I only just tumbled to what those venturi that you linked to are! I'd never seen them before ... They're not on my bike and never have been!



It's usualy better to start 'rich' and go leaner, so from what you've described I'd suggest starting with the 260s.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 7:25 am

Noted kommando! They do look restrictive, given how the air box is without them ... Thanks L.A.B. – well those inlets are opened up now, so...! I'll order a couple of 260s straight away. Although, my transmission is presently stripped out because it had got so noisy as to sound unsafe, so it'll be a while before I get to ride the thing again. The weather's not co-operating – I have to work outdoors – and I'm still waiting on one or two parts for the gearbox, so it'll be a week or two ... Thanks for all the tips!
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby seattle##gs » Sun Jul 23, 2017 12:02 pm

Have you tried moving the needle clip to a richer notch? If the motor loses steam above 70 MPH I think the slide is only 1/4 open or less using a 20 or 21 tooth sprocket. Try the needle position first and see what happens.

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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Jul 23, 2017 12:46 pm

Thanks, no I haven't tried that, I'll bear it in mind – cheers!
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