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MKIIA 850 carb needle: bean can vs peashooter

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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Thu Aug 10, 2017 2:51 pm

D'oh! Cue Cheese Shop Sketch quote – they're terrifically popular! Thanks again. But I see that the stay-up float kit that includes them is in stock ...! Maybe I'll get those then. But argh, the .106 needle jets are out of stock too! 'Tis the season, I suppose, they'll probably be overflowing in 6 months' time! :roll: I see that AN have the needle jets, but apparently they don't list the aluminium float needle. Around and around I go! The Post Office alone is making a small fortune out of me this summer. :(
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby acotrel » Thu Aug 10, 2017 3:00 pm

If you are using petrol, it probably would not be smart to make your own needle jets. But I wonder what the quality control is like with the stock items. Raising and lowering the needles provides a way of adjusting for differences in needle jet internal diameter, but what if you have two needle jets of slightly different ID and you are raising and lowering two needles together ?
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Thu Aug 10, 2017 3:03 pm

acotrel wrote:If you are using petrol, it probably would not be smart to make your own needle jets.

Thanks acotrel, but that's waaay beyond my skill set and equipment! About the order of doing things – jetting, timing etc. – I'm still at the stage of getting my ducks in a row for a starting point. But, as I hope you've read, there are already improvements! Cheers.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Thu Aug 10, 2017 3:56 pm

NortonMKIIA850 wrote:I see that AN have the needle jets, but apparently they don't list the aluminium float needle.


Surrey Cycles?
https://surreycycles.com/carburettors/m ... oncentric/

15. Needle Jet (State Size & 2 or 4 Stroke) – £5.00

18. Float Needle Aluminium – £5.00
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Thu Aug 10, 2017 4:21 pm


D'you know, I've been familiar with that name for years, but never tried them, no idea why ... I'll have a look at their website. But I've already placed orders at Amal and AN, thereby forking out for double the postage ... Still, I'm always thinking of things I meant to get from AN on the previous order, so there are a few other bits on their way from them too, making it slightly more worthwhile. Thanks again L.A.B., you're very kind.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Aug 13, 2017 10:51 am

Welp – thanks to super speedy deliveries from AN and Amal, both my carbs now have new 4-ring carb needles, new .106 needle jets, new 260 main jets, Stay-Up floats and aluminium float needles, viton-tipped of course! Fuel level in the left carb is kinda midway in the range 0.170" – 0.240" below the top of the float bowl, but in the right carb I could not get the fuel level above what I'm pretty sure is slightly below that range. I tried bending the tabs on the Stay-Up float and moving the needle valve seat, the only change I achieved was when the needle couldn't seat and fuel would've spouted out the top of the sight tube if I hadn't turned it off pdq! All very strange. To me anyway. In that one carb, for whatever reason, the top of the Stay-Up float appears to meet the underside of the carb body when I try to raise the fuel level. The idle/very low rpm mixture seems very weak, so idling is worse than before and there's a bit of popping on the overrun – of course that might be expected given what I just said – but naturally it gets much better once everything is well and truly warmed up. Maybe I need to make an appointment with a carb specialist. Do Surrey Cycles offer that sort of service, or just sell carbs and parts? I can ask them myself tomorrow ... Otherwise it's running very nicely indeed. Cheers.

p.s. Following Bushman's advice (http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html) I'm waiting for my son to break a guitar string, then I'll see what happens when I try cleaning the pilot jets ... When I first cleaned the carbs after the 12-year layup, cleaner spray seemed to pass fine through all the orifices, we shall see ...
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby Deets55 » Sun Aug 13, 2017 11:28 am

Colin,
I noticed something about the Stay Up floats that I have not seem mentioned here before. After adjusting the fuel level to the proper height, I noticed that when the float is in the full dropped position that it still does not lift up on the float needle. That indicates that fuel delivery depends solely on fluid pressure from the tank. I have never seen a carb that worked that way. A lot of needles have a spring that wraps around the float tang that will pull the needle off the seat as the fuel level drops. I tested a plastic float in another bowl and noticed that it will lift the needle as it drops. think the tang needs to be thicker so it both pulls and pushed the needle depending on need.
As an experiment I set the fuel level and then bent one tank up to pull the needle up off the seat as the fuel level in the bowl drops. I have close to 2,000 miles since I made the adjustments and not seem any negative affects. On the plus side I was able to get a higher fuel level and it will tickle a lot faster. I don't know if any of this is helpful but I thought I would share my findings.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Sun Aug 13, 2017 11:43 am

NortonMKIIA850 wrote:but in the right carb I could not get the fuel level above what I'm pretty sure is slightly below that range. I tried bending the tabs on the Stay-Up float and moving the needle valve seat, the only change I achieved was when the needle couldn't seat and fuel would've spouted out the top of the sight tube if I hadn't turned it off pdq! All very strange. To me anyway. In that one carb, for whatever reason, the top of the Stay-Up float appears to meet the underside of the carb body when I try to raise the fuel level.


Try checking the fuel level with the float bowl removed from the carb.

Deets55 wrote: I noticed something about the Stay Up floats that I have not seem mentioned here before. After adjusting the fuel level to the proper height, I noticed that when the float is in the full dropped position that it still does not lift up on the float needle.


Alloy or brass needles? The brass needles are heavy enough to shut off the fuel supply on their own with no help from the float (plastic or Stay-Up) which causes a low fuel level.

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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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby Deets55 » Sun Aug 13, 2017 11:59 am

Les,

Aluminum Viton tippedneedles in .125" bowls.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Sun Aug 13, 2017 12:07 pm

Deets55 wrote:Aluminum Viton tippedneedles in .125" bowls.


OK, well, I've only observed it with brass needles, and it didn't seem to matter if the floats were the white plastic or StayUp.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby Deets55 » Sun Aug 13, 2017 1:32 pm

L.A.B. wrote:
Deets55 wrote:Aluminum Viton tippedneedles in .125" bowls.


OK, well, I've only observed it with brass needles, and it didn't seem to matter if the floats were the white plastic or StayUp.


Thanks Les,
I'm chasing a problem like Colin but farther up in the RPM range. I think I got narrowed down to fuel flow under hard acceleration, in top gear, after running through the gears. Petcocks will flow 500cc/min each, flow measured through drain plug is 200cc/min (checking one carb at a time). I even cut slots in the float valve to get more flow. Fortunately it only happens in a range I never travel in. I'm not overly concerned with it, but would like to get it straightened out.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Sun Aug 13, 2017 1:56 pm

Deets55 wrote:After adjusting the fuel level to the proper height, I noticed that when the float is in the full dropped position that it still does not lift up on the float needle. That indicates that fuel delivery depends solely on fluid pressure from the tank.

As an experiment I set the fuel level and then bent one tank up to pull the needle up off the seat as the fuel level in the bowl drops. I have close to 2,000 miles since I made the adjustments and not seem any negative affects. On the plus side I was able to get a higher fuel level and it will tickle a lot faster.


Thanks for sharing Pete, very interesting! I was too absorbed in the fuel level to notice the effect you mention – nor did it occur to me to compare the two different types of float for the height between the tangs and the tops of the floats, that might be interesting too and I'll check both things next time, maybe tomorrow. Cheers.

L.A.B. wrote:Try checking the fuel level with the float bowl removed from the carb.


Good idea L.A.B., thanks again, I'll do that! Cheers.
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby NortonMKIIA850 » Mon Aug 14, 2017 8:55 am

L.A.B. wrote:Try checking the fuel level with the float bowl removed from the carb.


Good idea L.A.B., thanks again, I'll do that! Cheers.

Later: I've now had the 'problem' bowl from my right carb, plus Stay-Up float and aluminium float needle, off the bike and set up with the fuel hose attached plus the sight hose up the side for good measure – I got around the issue of only having a fuel hose for two carbs by setting up an old, spare float bowl alongside. Having done it this way, I can see that this kind of 'bench testing' is the only really reliable way, and I'd never have tried it but for L.A.B.'s suggestion, so thanks again for that. Problem is, as Pete reported, I found that the Stay-Up float doesn't lift the needle off its seat, so I felt that there was no way of knowing at precisely which point the float stopped rising as I injected fuel into the hose, short of shelling out for a dial gauge – sorry, I don't have one. I held the float spindle down with a cocktail stick btw, so my fingers were well out of the way. I guesstimated the setting for the float by poking the float down into the fuel with another cocktail stick and listening/feeling for the float clunking against the needle as it popped back up. Anyway, whether bending the float tabs or moving the needle valve seat, I couldn't get a fuel level up within the desirable range without the float reaching for the sky. I have to admit that I'm now very tired of the fiddle-faddle, mostly because I have to do it all in my kitchen (with doors etc wide open) while leaving tools etc in the street, vulnerable to passers-by. I'm sure this contributed to my problems. I'll try again another time, when my patience levels are restored! I expect I could improvise a measurement of when the float stops rising with a bit of bent wire ...
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby L.A.B. » Mon Aug 14, 2017 10:08 am

NortonMKIIA850 wrote:Problem is, as Pete reported, I found that the Stay-Up float doesn't lift the needle off its seat, so I felt that there was no way of knowing at precisely which point the float stopped rising as I injected fuel into the hose,


Even with a reasonably low head of fuel, the alloy needle should be forced off the seat by the head of pressure, it shouldn't rely on the float tang physically lifting the needle off its seat as is often the case with the heavier brass needle.


You reported the low fuel level problem before you fitted the StayUp float so I doubt the float is the actual cause. It's also possible to reproduce the same 'no needle lift' situation with the white floats by raising the seating too high so I don't exactly agree it only applies to the StayUp foats, after all, the other carb fuel level is where it should be.
When you bent the StayUp tangs, are you sure you bent only the tangs as it's important not to bend the arms of the float?



NortonMKIIA850 wrote: short of shelling out for a dial gauge – sorry, I don't have one. I guesstimated the setting for the float by poking the float down into the fuel with another cocktail stick and listening/feeling for the float clunking against the needle as it popped back up. Anyway, whether bending the float tabs or moving the needle valve seat, I couldn't get a fuel level up within the desirable range without the float reaching for the sky.


I would say there's a fair chance the seating in that particular float bowl, for whatever reason, is too high. Maybe tap it out and check there's no dirt trapped beneath it? You didn't happen to measure the depth of the needle seating by any chance?
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Re: MKIIA 850 carb needle: bean can vs peashooter

Postby Deets55 » Mon Aug 14, 2017 10:43 am

Even with a reasonably low head of fuel, the alloy needle should be forced off the seat by the head of pressure, it shouldn't rely on the float tang physically lifting the needle off its seat as is often the case with the heavier brass needle.


Les,
One thing I did notice was the issue I am having was less pronounced with a full tank of gas as opposed to a half of tank. So I will assume that head pressure will affect how much fuel flows pass the needle.
As far as the float not needing to lift the needle, I wonder if maximum fuel flow can be obtained by simply relying on fluid pressure as opposed to the needle being opened completely by the float tang. When cruising on the highway and opening the throttle I don't seem to get a starvation issue, but when doing a WOT 1/2 mile sprint I have a problem. I'm in triple digits by then so every test is a risk I really don't want ( or need) to take. It just seems that the bowl runs out of fuel. Nothing scientific here just seat of the pants observations.
I contacted Amal about just buying float seats ( I have extra bowls) to experiment with but have yet to get a response from them.
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