MKIIA 850 carb needle: bean can vs peashooter

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acotrel said:
Popping on the over-run is usually an indication of a leak in the exhaust system. A flat spot or a cough when you use the throttle is the usual symptom of lean jetting. It will happen if you ride the bike without warming it up, when you have got the jetting right. However,it should not happen when the motor is warm.
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Agreed, but for example last year my old Yamaha TR1 was struggling on small throttle openings, and spitting back through the carbs when cold, then once warm it would pop and backfire through the exhausts on the overrun. It turned out to be a split in the rubber carb mount on one pot.
 
cliffa said:
That's interesting L.A.B. I wonder if Burlen have changed something? As you can see earlier in the thread when I set the fuel level correctly, the top of the stay up was approx 8mm above the top of the bowl.
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You were using petrol and not another fluid (water) by any chance (sorry but I had to ask)?


cliffa said:
When I called Burlen, they said "yes, some do that" and to set the top of the float level with the top edge of the float bowl. (which sets the fuel level below the recommended height).
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That is odd, as the StayUp floats have been in production for nearly 8 years now :shock: so if there had been a significant problem with them, then I would have expected to have heard more about it by now, not just on Access Norton but other forums? :?
 
L.A.B. said:
cliffa said:
That's interesting L.A.B. I wonder if Burlen have changed something? As you can see earlier in the thread when I set the fuel level correctly, the top of the stay up was approx 8mm above the top of the bowl.
Click to expand...

You were using petrol and not another fluid (water) by any chance (sorry but I had to ask)?


cliffa said:
When I called Burlen, they said "yes, some do that" and to set the top of the float level with the top edge of the float bowl. (which sets the fuel level below the recommended height).
Click to expand...


That is odd, as the StayUp floats have been in production for nearly 8 years now :shock: so if there had been a significant problem with them, then I would've thought we'd have heard more about it by now, not just on Access Norton but other forums? :?
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Liquid helium :D

no seriously, petrol. It was 50:1 mix for my leaf sucker but i don't think that would make any difference do you?

I'm sure I've seen some other threads about the same issue, I'll have to see if I can find them.
 
L.A.B. I've found one thread from 2013 so it's definately not a new issue...


Confused readings w/ Stay Up Float.

Ok Im as sick of this as Im sure most are but still need to figure it out. For some reason when adjusting the Fuel level in my M1Concentric with the new "stay up float" to the .210 +_ .040 just as a friends did the top of my float is sticking up about 1/4" above the top of the float bowl whitch...
www.accessnorton.com www.accessnorton.com
 
cliffa said:
L.A.B. I've found one thread from 2013 so it's definately not a new issue...


Confused readings w/ Stay Up Float.

Ok Im as sick of this as Im sure most are but still need to figure it out. For some reason when adjusting the Fuel level in my M1Concentric with the new "stay up float" to the .210 +_ .040 just as a friends did the top of my float is sticking up about 1/4" above the top of the float bowl whitch...
www.accessnorton.com www.accessnorton.com
Click to expand...

Later the OP says:

Confused readings w/ Stay Up Float.

Ok Im as sick of this as Im sure most are but still need to figure it out. For some reason when adjusting the Fuel level in my M1Concentric with the new "stay up float" to the .210 +_ .040 just as a friends did the top of my float is sticking up about 1/4" above the top of the float bowl whitch...
www.accessnorton.com www.accessnorton.com

gtsun said:
One thing I noticed was my pin that the float pivots on was worn & it's a real sloppy fit. It also is slightly higher than the groove. The gasket probobly takes that up but mine was trashed so I bought a # 37 drill blank & cut it to fit & took down the ends a bit so it doesn't interfear with the gasket sealing. I'm using one of the aluminum Viton tip float needles & in my tests with a gas line hooked up it seals fine, no leaks. I'm doing one for my BSA 441 too, wish I could find a forum for that bike as easy to navigate etc as this one... Anyway, fingers crossed all will be fine. Thanks.
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What also has to be taken into consideration is that both the needle seating and pin groove depths were altered at various times.

http://www.britcycle.com/Manuals/Amal_F ... 622069.pdf

1966-72

The original float chambers were fitted from 1966 to 1972 with the drain plug being introduced in 1970. The depth of the needle valve seating from the top edge of the float bowl to the floor of the seating measures 0.588”.

Other distinguishing features are:

The top of the seat fits flush with the surrounding alloy.
Pressure on the float tags to hold the needle valve shut will cause the float to protrude above the top of the bowl by an angle of approximtely 5 degrees.

This seating depth produces a fuel level very near the top end of the correct range, and small variations in float weight, float tag position and float needle wear can produce a carburettor that runs excessively rich and in extreme circumstances cause the floats to foul the top of the float chamber. These float chambers also have shallower float spindle slots than later versions. To improve the fuel level in these bowls it is necessary to eitherr adjust the needle seat to achieve a depth of around 0.565” or adjust the tangs of the StayUP float so that the far edge of the float sits 0.080” below the top of the float bowl. The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved. Moving the float needle seat up or down is an operation that should only be attempted as a last resort as it is possible to damage or loosen the seat, effectively destroying the float bowl. Remove the float, needle valve and banjo bolt, and heat the bowl by immersing it in a suitable container of boiling water. Use a 1/8” diameter rod to gently tap the seat up, or a suitable drift that will not damage the valve seat to move it down, until the proper setting is attained.

1972 to Present

The 0.588’ seating depth was modified in May 1972 to 0.579”. In April 1974 an adjustment to the slots for the float spindle also lowered the float. The seating depth was further reduced to 0.574” in May 1986 and has remained as that ever since. In this position the fuel level is correct when the top surface of the float is parallel with and just above the top of the float chamber when the valve is closed. This position is also correct for the floats in the Mark 2 Series of carburettors. Some minor adjustment of the float tangs may be useful to achieve balance between cylinders but there should be no need for significant adjustment unless the needle seating has previously been disturbed or it is intended to experiment with different fuel levels for performance purposes. It should also be noted that to promote the most efficient operation of the carburettor it is important to ensure that there are no obstructions in petrol taps or banjo filters to prevent the maximum possible rate of fuel flow.
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The pin also needs to be clamped firmly down into its slot as it would normally be by the gasket.
 
kommando said:
Before shelling out for richer slides make the pilot mixture richer and test, if the flat spot reduces then richer cutaways will work. But first check the slides are lifting in unison as one lifting first will give same symptoms is flat spot on opening throttle.
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I was at the Carole circuit near Paris last week-end with my 1969 Triumph :mrgreen: Daytona racer and although it was running fine at medium and high revs it was definitely sluggish below 4K. Raising the needles a couple of notches helped a bit but still no cigar. I then replaced the standard 106 needle jets by 107 ones and the problem was spectaculary solved instantly.
 
Well, no air leaks found, enriching the pilot circuits by turning both screws in by ¼ turn does reduce the popping – that was a good idea, per Holmes & Watson it seems obvious now! I forgot to mention, I balanced the carbs via Bushman's 'shop' method only a week or two ago and haven't so much as taken the tank off since, so ... It looks like I need to try size 3 slides ... And the StayUps are on their way back to Burlen, I wonder what they'll say. L.A.B., I've read that history of the Concentric before, and now I've looked at the thread that was linked, but I didn't see anything that might explain my experience, thanks for sharing anyway! The carbs were new via Mick Hemmings in 1999, I have the invoice, so surely their parameters are suitable for the StayUps.

p.s. Looking at Andover Norton's online shop, it occurs to me that, apart from the plastic airbox, which we've established is not restrictive without the venturi, the only things left in my induction and exhaust systems that are specified for the MK2A are the 3½ slides and the 4-ring needles. I've just ordered size 3 slides, but should I be trying 2-ring needles as well? This leads me to ask, what exactly is the difference between 2-ring and 4-ring needles? I don't recall seeing this explained anywhere.
 
what exactly is the difference between 2-ring and 4-ring needles?
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The lengths and/or taper are different to suit the different spray tubes, can't remember which is which. Unless you plan to change the spray tubes I would stick with the matching needle for the slotted spray tube.
 
Thanks kommando and L.A.B. Previously, in the course of this thread, I discovered that the carbs I bought via Mick Hemmings (well, Angela really!) in 1999 actually had 2-ring needles, as well as stepped spray tubes! Hence the confusion. I recently fitted 4-ring needles, following received wisdom for the MK2A. I consider myself told now, to stick with 4-ring needles! But I'm still left wondering what the physical difference is ... Cheers!
 
L.A.B. said:
What also has to be taken into consideration is that both the needle seating and pin groove depths were altered at various times.

http://www.britcycle.com/Manuals/Amal_F ... 622069.pdf

1966-72

The original float chambers were fitted from 1966 to 1972 with the drain plug being introduced in 1970. The depth of the needle valve seating from the top edge of the float bowl to the floor of the seating measures 0.588”.

Other distinguishing features are:

The top of the seat fits flush with the surrounding alloy.
Pressure on the float tags to hold the needle valve shut will cause the float to protrude above the top of the bowl by an angle of approximtely 5 degrees.

This seating depth produces a fuel level very near the top end of the correct range, and small variations in float weight, float tag position and float needle wear can produce a carburettor that runs excessively rich and in extreme circumstances cause the floats to foul the top of the float chamber. These float chambers also have shallower float spindle slots than later versions. To improve the fuel level in these bowls it is necessary to eitherr adjust the needle seat to achieve a depth of around 0.565” or adjust the tangs of the StayUP float so that the far edge of the float sits 0.080” below the top of the float bowl. The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved. Moving the float needle seat up or down is an operation that should only be attempted as a last resort as it is possible to damage or loosen the seat, effectively destroying the float bowl. Remove the float, needle valve and banjo bolt, and heat the bowl by immersing it in a suitable container of boiling water. Use a 1/8” diameter rod to gently tap the seat up, or a suitable drift that will not damage the valve seat to move it down, until the proper setting is attained.

1972 to Present

The 0.588’ seating depth was modified in May 1972 to 0.579”. In April 1974 an adjustment to the slots for the float spindle also lowered the float. The seating depth was further reduced to 0.574” in May 1986 and has remained as that ever since. In this position the fuel level is correct when the top surface of the float is parallel with and just above the top of the float chamber when the valve is closed. This position is also correct for the floats in the Mark 2 Series of carburettors. Some minor adjustment of the float tangs may be useful to achieve balance between cylinders but there should be no need for significant adjustment unless the needle seating has previously been disturbed or it is intended to experiment with different fuel levels for performance purposes. It should also be noted that to promote the most efficient operation of the carburettor it is important to ensure that there are no obstructions in petrol taps or banjo filters to prevent the maximum possible rate of fuel flow.
Click to expand...

The pin also needs to be clamped firmly down into its slot as it would normally be by the gasket.
Click to expand...


Hi L.A.B. luckily the P.O. had fitted premiers, but he admitted they never got dialed in. When I got it, It was "ticking over" at around 2000 rpm, I've obviously lowered it but the tick-over is really unreliable. When checking I found both fuel levels to be way too low. The float pivots actually click into the locating slots and hardly need holding down at all, so that's not my issue. The floats just seem overly buoyant.

I find this bit of the Burlen instruction slightly misleading "The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved "

If you are holding the tangs in a vice, then surely you are bending the arms which connect to the float, and not the tangs?

I bought a Madass single cable linkage which I hope to fit this weekend, so I'll check that the seats are not set too low in the bowls.

Cheers,

cliffa
 
cliffa said:
I find this bit of the Burlen instruction slightly misleading "The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved "

If you are holding the tangs in a vice, then surely you are bending the arms which connect to the float, and not the tangs?
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Possibly?
As I remember it, only one out of the four StayUps required a minor adjustment and I didn't use Burlen's method. None looked like the one in your photo.

I still recommend the pin is held down. This is the test rig I use, unfortunately, the floats pictured are not StayUps.
MKIIA 850 carb needle: bean can vs peashooter
 
L.A.B. That's impressive! thanks for posting.

I'll give that a go as well. By the way, out of interest were you setting the float height or the fuel height?
 
cliffa said:
By the way, out of interest were you setting the float height or the fuel height?
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If I remember correctly, I took that photo whilst I was checking Burlen's statement regarding brass float needles causing a lower fuel level and comparing the difference in fuel level between brass and aluminium needles.

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.
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I've just got back from a blast on the bike after fitting hard-anodised size 3 slides, instead of size 3½s, and it's transformed – no flat spot, no popping on the overrun, joyful out on the road, and perfectly happy in town! Halleluia – deep breath, and relax ...!

I'm extremely grateful for all the help and support in the course of this thread, without which I'm not sure I'd have got where I am now. But d'you know, I don't think I've ever encountered any clear advice on how to set up the carbs on an 850 if it left the factory with the black, plastic air box and bean-can silencers, but now has the same air box and peashooters. From today's developments, I wonder if I've finally cracked it! Thing is, I've learned to be wary of Andover Norton's online shop's part identifications over the years, but lately I have noticed improvements. So, when I noticed the other day that 3½ slides are qualified there as being for the MK2A, but otherwise are listed alongside size 3s for 850s, a penny dropped – barring the black plastic air box, my bike's no longer set up like a MK2A! The size 3 slide listed there must therefore be for 850s with 260 main jets (and 4-ring needles), which I now have! Sherlock Holmes would probably be shaking his head in despair ... As indeed some of you might be. Anyway, this sums up what I've done:
1. Make sure the plastic air box does not have the rubber venturi over the main intakes – remove them if present – and clean or replace the air filter, remembering to oil it, it doesn't take much.
2. Replace the 230 main jets with 260s.
3. Fit new, standard, .106 needle jets – they will be worn – and, if in doubt, new 4-ring needles – they last much longer because they are fairly free to rotate, and so wear more slowly.
4. Replace the size 3½ throttle slides with size 3s.
5. Clean the pilot bushes with a 0.016" or 0.4mm probe.
6. Balance the carbs.
And away you go!
Phew ... And I've only had the bike nearly 20 years! If it all goes pear-shaped I'll let you know, but for now it feels like a new bike ... One other thing – since fitting the first pair of hard-anodised slides, direct replacements at size 3½, fuel consumption has improved: it's gone from the mid-to-high 40s mpg to between 53 and 55 mpg. The size 3 slides are of course richer, so we'll see. The only other variable is that I have unbalanced downpipes, whereas the bike would've had balanced ones from new. I ought also to give an honourable mention here to Bushman's page on these carbs, it doesn't give the full picture but is a very handy, practical guide – https://www.ntnoa.org/pdf/Bushmans Carb Tuning Secrets.pdf

About the StayUp floats, I returned mine to Burlen and the word is that, when tested, they seemed to be too low! A reeeally helpful chap suggested I send him a pair of float bowls that he would then set up for me, so I should just be able to fit them and go when I get them back. I've sent them, and await a minor miracle! Cheers!
 
NortonMKIIA850 said:
But d'you know, I don't think I've ever encountered any clear advice on how to set up the carbs on an 850 if it left the factory with the black, plastic air box and bean-can silencers, but now has the same air box and peashooters. From today's developments, I wonder if I've finally cracked it! Thing is, I've learned to be wary of Andover Norton's online shop's part identifications over the years, but lately I have noticed improvements. So, when I noticed the other day that 3½ slides are qualified there as being for the MK2A, but otherwise are listed alongside size 3s for 850s, a penny dropped – barring the black plastic air box, my bike's no longer set up like a MK2A! The size 3 slide listed there must therefore be for 850s with 260 main jets (and 4-ring needles), which I now have! Sherlock Holmes would be shaking his head in despair ... As indeed some of you might be.
Click to expand...

The 3½ slides (stepped spray tubes and 4 ID ring needles) were supposedly standard for all 850 carbs including non-'A' (with 260 main jets).
amalcarb-info.php
850 "Throttle Valve" all 928/06035 (928/060 3.5).

3½ is what's listed in the factory manual 850 carb spec. (260 main, 928/104 needle, 928/107 stepped spray tube) and also the original Amal Norton Commando carb list, so the slide/needle information on the AN website appears to be wrong, for one thing, they list only the 928/107 stepped spray tube which is only used with the 4 ID ring needle.
Only the stepped spray tube and 4 ID needle are listed in the parts books for the 850.


Accoding to AN, the 850 float bowl is now 0.125" seating, 622/056 which doesn't match the '73-'74 parts lists, only 850 Mk3.
 
L.A.B. said:
The 3½ slides (stepped spray tubes and 4 ID ring needles) were supposedly standard for all 850 carbs including non-'A' (with 260 main jets).
amalcarb-info.php
850 "Throttle Valve" all 928/06035 (928/060 3.5).

3½ is what's listed in the factory manual 850 carb spec. (260 main, 928/104 needle, 928/107 stepped spray tube)
Click to expand...
True that, about the manual – I could've checked there but, in my naiveté, for once I trusted AN – however, it has inspired revelatory behaviour in my bike so I'm happy! For as long as it lasts, anyway, and I hope that'll be a very long time ... I'll take the dear old thing out for another blast today, just to prove that yesterday was neither a dream nor an aberration.
 
NortonMKIIA850 said:
Thanks kommando and L.A.B. Previously, in the course of this thread, I discovered that the carbs I bought via Mick Hemmings (well, Angela really!) in 1999 actually had 2-ring needles, as well as stepped spray tubes! Hence the confusion. I recently fitted 4-ring needles, following received wisdom for the MK2A. I consider myself told now, to stick with 4-ring needles! But I'm still left wondering what the physical difference is ... Cheers!
Click to expand...
 

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