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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: JubeePrince]
#425226
03/20/12 6:52 am
03/20/12 6:52 am
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Joined: Apr 2006
Posts: 1,397 New Zealand
johnm
BritBike Forum member
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Posts: 1,397
New Zealand
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Are you sure there is such a thing as a aluminium/viton tip ?
I asked Burlen about this some time ago after seeing an illustration of one on their website. They told me it was a mistake and there is no aluminium/viton tip.
It may possibly have changed because this was about 2 years ago but they definitly told me no back then.
There is an aluminium only needle but this is for alcohol and you do not want to use this because they are very difficult to seal and stop leaking. I have personal experience of this.
Last edited by johnm; 03/20/12 6:53 am.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: johnm]
#425242
03/20/12 11:32 am
03/20/12 11:32 am
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Joined: Aug 2007
Posts: 160 England
Paul744
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Joined: Aug 2007
Posts: 160
England
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Are you sure there is such a thing as a aluminium/viton tip ?
Yes, I've just bought some.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Paul744]
#425246
03/20/12 12:03 pm
03/20/12 12:03 pm
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Joined: Aug 2001
Posts: 6,892 Vermont
Jon W. Whitley

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Did you get those direct from AMAL ? Yes, I've just bought some.
Jon W.
1957 6T Thunderbird 650 1968 T100R Daytona 500 1971 TR6R Tiger 650 1970 BSA A65F 650 1955 Tiger 100 - Project
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: JubeePrince]
#425250
03/20/12 12:24 pm
03/20/12 12:24 pm
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Joined: Aug 2001
Posts: 7,310 scotland
triton thrasher
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My bike runs better with the new alloy needles, but it had a definite problem with vibration causing flooding.
There may be less, or no benefit to your bike.
Amateur Loctite enthusiast.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Pete R - R.I.P.]
#425263
03/20/12 2:05 pm
03/20/12 2:05 pm
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Joined: Nov 2005
Posts: 7,334 Back on the mainland!
JubeePrince
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The viton tipped aluminium needle weighs 0.5 gram.This will give you the same fuel level,as long as you have a fuel head 5.5" above the bottom of the float bowl.That means it will work OK if there is some fuel in the tank.It takes 5.5" of fuel head to overcome the weight of the needle.If there isn't enough fuel head to overcome the needle weight,the fuel level in the bowl will be about 0.200" lower than it should be.The float is being used to open the needle,instead of closing it.
The viton-tipped brass needle weighs 1.7 gram.It takes about 13" or 14" of fuel head (above the bottom of the bowl) to overcome the weight of this needle.With less fuel than that,the only chance you have of getting the correct fuel level in the bowl is if vibration is lifting the needle off its seat. If the fuel level ever became high enough,the float would then hold the needle closed.
So if I understand you correctly Pete, you're saying that with the brass needle and partially filled tank that the mixture would be too lean? (Assuming all things being equal, properly jetted, float height correct, etc). When you say fuel head, what does that mean exactly? The height of the fuel in the tank and fuel line? Steve
Last edited by JubeePrince; 03/20/12 2:06 pm. Reason: mixture would be...
'77 T140J "Vintage Bike". What's in your garage?
"The paying customer is always right."
Fitting round pegs into square holes since 1961...
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Pete R - R.I.P.]
#425265
03/20/12 2:12 pm
03/20/12 2:12 pm
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Joined: Nov 2011
Posts: 4,293 U.S.
Magnetoman

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The original nylon needle weighed 0.3 gram. This should give you a fuel level 0.205" +/- 0.035" below the top of the bowl,when the float toe is set 0.080" below the top of the bowl. The viton tipped aluminium needle weighs 0.5 gram.This will give you the same fuel level,as long as you have a fuel head 5.5" above the bottom of the float bowl.That means it will work OK if there is some fuel in the tank.It takes 5.5" of fuel head to overcome the weight of the needle. I'm in an airport waiting for a weather-delayed flight, so I haven't taken the time to reverse engineer your calculation, but it appears you've calculated the pressure of a column of gasoline (pounds/sq. inch, or grams/sq. cm) and equated that to the mass difference. If so, that's an incorrect calculation. And, it's not how the float needle works anyway. The needle is pushed against the seat by the float acting through a ~4:1 lever arm, and flow ceases when the pressure on the seat equals or exceeds the pressure head of the fuel in the tank above. It's true that the float has to lift a bit more weight if the needle is brass instead of plastic or Al, but that's a minor effect. The level of the gasoline just has to rise enough around the large float to displace the additional 1 gram (or whatever) of weight, at which point the pressure on the seat will be the same as if the needle weighed less. Since there's no AMAL handy in the airport to measure, I'll guess that the cross section of a float is ~2.5 cm, so the area immersed in fuel is ~6 cm^2. If the fuel level rises an additional 0.1 cm (i.e. only 0.039", which is within the specs needed to set the level) above where it was with a plastic needle, it will displace 0.6 cm^3 of fuel. The density of gasoline is less than that of water (1 gm/cm^3), so rather than googling it let's guess it's 0.6 gm/cm^3 to make the calculation simple. That's 0.6 grams of additional fuel that has been displaced. With the 4:1 leverage, this means the rise of only ~0.04" of the fuel in the bowl will lift a needle weighing 2.4 grams more than the plastic needle. So, the weight of the needle does affect the height of the fuel in the bowl, but by very little.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Magnetoman]
#425266
03/20/12 2:22 pm
03/20/12 2:22 pm
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Joined: Nov 2008
Posts: 2,740 Bishop, Calif.
desco
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Posts: 2,740
Bishop, Calif.
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Why I love this web site.
1968 T120R 1972 T120RV Any advice given is without a warranty expressed or implied.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: JubeePrince]
#425311
03/20/12 6:35 pm
03/20/12 6:35 pm
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Joined: Aug 2001
Posts: 7,310 scotland
triton thrasher
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Posts: 7,310
scotland
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The free play between the float's fork and the needle surfaces above and below it is noticeably huge on a Concentric. A Monobloc float, which lifts the needle to close the valve, looks like it would work properly the way Magnetoman describes. I experimented with narrowing the gap on a Concentric, but didn't really get anywhere.
Amateur Loctite enthusiast.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: triton thrasher]
#425321
03/20/12 7:36 pm
03/20/12 7:36 pm
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Joined: Nov 2011
Posts: 4,293 U.S.
Magnetoman

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The free play between the float's fork and the needle surfaces above and below it is noticeably huge on a Concentric. A Monobloc float, which lifts the needle to close the valve, looks like it would work properly the way Magnetoman describes. I experimented with narrowing the gap on a Concentric, but didn't really get anywhere. In transit at DFW so again brief. Gravity acting on needle helps open it on Monobloc and close it on Concentric but, as my earlier post showed, effect on fuel level is tiny in both cases. Only one side of groove matters. Float always pushes on it. The amount of play in groove doesn't matter.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Jon W. Whitley]
#425327
03/20/12 8:02 pm
03/20/12 8:02 pm
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Joined: Aug 2007
Posts: 160 England
Paul744
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Did you get those direct from AMAL ? My parts man gets them direct from AMAL. HTH
Last edited by Paul744; 03/20/12 8:02 pm.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Magnetoman]
#425337
03/20/12 8:46 pm
03/20/12 8:46 pm
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Joined: Aug 2001
Posts: 7,310 scotland
triton thrasher
BritBike Forum member
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BritBike Forum member
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Posts: 7,310
scotland
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The original nylon needle weighed 0.3 gram. This should give you a fuel level 0.205" +/- 0.035" below the top of the bowl,when the float toe is set 0.080" below the top of the bowl. The viton tipped aluminium needle weighs 0.5 gram.This will give you the same fuel level,as long as you have a fuel head 5.5" above the bottom of the float bowl.That means it will work OK if there is some fuel in the tank.It takes 5.5" of fuel head to overcome the weight of the needle. I'm in an airport waiting for a weather-delayed flight, so I haven't taken the time to reverse engineer your calculation, but it appears you've calculated the pressure of a column of gasoline (pounds/sq. inch, or grams/sq. cm) and equated that to the mass difference. If so, that's an incorrect calculation. And, it's not how the float needle works anyway. The needle is pushed against the seat by the float acting through a ~4:1 lever arm, and flow ceases when the pressure on the seat equals or exceeds the pressure head of the fuel in the tank above. It's true that the float has to lift a bit more weight if the needle is brass instead of plastic or Al, but that's a minor effect. The level of the gasoline just has to rise enough around the large float to displace the additional 1 gram (or whatever) of weight, at which point the pressure on the seat will be the same as if the needle weighed less. Since there's no Amal handy in the airport to measure, I'll guess that the cross section of a float is ~2.5 cm, so the area immersed in fuel is ~6 cm^2. If the fuel level rises an additional 0.1 cm (i.e. only 0.039", which is within the specs needed to set the level) above where it was with a plastic needle, it will displace 0.6 cm^3 of fuel. The density of gasoline is less than that of water (1 gm/cm^3), so rather than googling it let's guess it's 0.6 gm/cm^3 to make the calculation simple. That's 0.6 grams of additional fuel that has been displaced. With the 4:1 leverage, this means the rise of only ~0.04" of the fuel in the bowl will lift a needle weighing 2.4 grams more than the plastic needle. So, the weight of the needle does affect the height of the fuel in the bowl, but by very little. When you have time, please start again and make it brief. I'm baffled: a rise in the fuel level in the bowl of a Concentric doesn't lift the needle. It lifts the float, which pushes the needle down.
Amateur Loctite enthusiast.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: JubeePrince]
#425367
03/20/12 11:29 pm
03/20/12 11:29 pm
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Joined: Mar 2005
Posts: 10,087 Boston, Massachusetts
John Healy

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Posts: 10,087
Boston, Massachusetts
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As for me, I like the old nylon needles as they seem to cause me less problems. Bob, you must excuse me (and please take no offense) as I find this amusing as I am old enough, and been distributing these this for way too long, and remember everyone complaining about the nylon needles. That is why we got the brass ones in the first place. I guess we didn't know how well we had it. Could the mass collective of British enthusiasts have had brass needle envy as Mikuni's came with them and we didn't want to be left behind... This discussion is as old as AMAL brass needles themselves...
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Magnetoman]
#425368
03/20/12 11:30 pm
03/20/12 11:30 pm
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Joined: Jul 2009
Posts: 3,549 Vic. Australia
Pete R - R.I.P.
In Remembrance
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In Remembrance
Joined: Jul 2009
Posts: 3,549
Vic. Australia
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Only one side of groove matters. Float always pushes on it. The amount of play in groove doesn't matter.
This is not the case,when needle weight alone is enough to overcome fuel pressure and prevent fuel flowing into the bowl.With a brass needle,this will happen when the tank fuel level is below about 3/4 full. The needle then needs to be lifted by the float (or some other means) to allow fuel into the bowl.For the float to lift the needle,it must drop a long way and operate on the other side of the needle groove.The float will drop this amount only if the fuel level in the bowl drops too.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Paul744]
#425400
03/21/12 2:46 am
03/21/12 2:46 am
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Joined: Aug 2001
Posts: 6,892 Vermont
Jon W. Whitley

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Vermont
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Thanks Paul. Just wanted to narrow the origin down a bit. My parts man gets them direct from AMAL. HTH
Jon W.
1957 6T Thunderbird 650 1968 T100R Daytona 500 1971 TR6R Tiger 650 1970 BSA A65F 650 1955 Tiger 100 - Project
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: triton thrasher]
#425407
03/21/12 3:37 am
03/21/12 3:37 am
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Joined: Nov 2011
Posts: 4,293 U.S.
Magnetoman

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When you have time, please start again and make it brief. I'm baffled: a rise in the fuel level in the bowl of a Concentric doesn't lift the needle. It lifts the float, which pushes the needle down. After a long day of delayed flights, followed by a great meal with lots of single malt whiskey and wine, I'm finally in my hotel room. Still, I'd like to go to sleep, so I'll keep this brief. Indeed, just as you say (and as I said, albeit in a more lengthy way), a rise in fuel level in a Concentric pushes the needle down against the seat and stops the flow. In this endeavor it is helped in a teensy way by gravity acting on the weight of the needle, which pulls a brass needle down a bit harder than it does a nylon needle. As a result, if a nylon needle were replaced by a brass needle of *precisely* the same dimensions, and if nothing else were changed, the float level would be lowered by ~0.04" or so after the substitution. This is a negligible amount. Since the float in a Monobloc pushes the needle up, the same principle is true for it, except it works in the opposite direction. That is, the float level would be raised by ~0.04" or so after the same substitution.
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: Pete R - R.I.P.]
#425409
03/21/12 4:07 am
03/21/12 4:07 am
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Joined: Nov 2011
Posts: 4,293 U.S.
Magnetoman

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Only one side of groove matters. Float always pushes on it. The amount of play in groove doesn't matter.
This is not the case,when needle weight alone is enough to overcome fuel pressure and prevent fuel flowing into the bowl.With a brass needle,this will happen when the tank fuel level is below about 3/4 full. The needle then needs to be lifted by the float (or some other means) to allow fuel into the bowl.For the float to lift the needle,it must drop a long way and operate on the other side of the needle groove.The float will drop this amount only if the fuel level in the bowl drops too. You would be correct for a Concentric (not a Monobloc) if the needle weight was high enough that the pounds/in^2 (or grams/cm^2) it exerted on the surface area of the seat due to gravity were large enough to overcome the pounds/in^2 of the pressure head of the fuel above it. I'm going to bed now, but urge you to do this calculation and post the result.
Last edited by Magnetoman; 03/21/12 7:55 pm. Reason: deleted duplicate quotation
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Re: Amal float needle: Brass/viton vs. aluminum/viton
[Re: John Healy]
#425469
03/21/12 3:22 pm
03/21/12 3:22 pm
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Joined: Nov 2005
Posts: 7,334 Back on the mainland!
JubeePrince
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This discussion is as old as Amal brass needles themselves...
John - I assume you're talking about brass vs. nylon and not brass vs. aluminum. If the latter, I'd love to hear your thoughts on it. Perhaps I'll shell out a few bucks and try the aluminum ones myself and post the results (or lack of) here. Steve
'77 T140J "Vintage Bike". What's in your garage?
"The paying customer is always right."
Fitting round pegs into square holes since 1961...
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