Fuel banjos

01dlx

01dlx

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Jun 27, 2022
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Hi all , I've rebuilt my carburetors and I'm replacing the nylon banjos with metal ones . Would it be possible to use Amal 150 degree x 5/16th banjos Part 376/139 ?

Thanks , Dave
 
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01dlx said:
Hi all , I've rebuilt my carburetors and I'm replacing the nylon banjos with metal ones . Would it be possible to use Amal 150 degree x 5/16th banjos Part 376/139 ?

Thanks , Dave
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They work find with the carbs but not with the hamcan air filter. You need the 180 degree metal ones which are 1/4". No idea why Norton used 1/4" and most others 5/16"
 
marshg246 said:
No idea why Norton used 1/4" and most others 5/16"
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There would seem to be no practical reason to use 5/16" as the restriction through the fuel tap is considerably less than even 1/4" and the standard float needle valve seat drilling is only 0.100".
 
L.A.B. said:
There would seem to be no practical reason to use 5/16" as the restriction through the fuel tap is considerably less than even 1/4" and the standard float needle valve seat drilling is only 0.100".
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Agreed, but then you hear people here saying to open both petcocks for high speed.
 
marshg246 said:
Agreed, but then you hear people here saying to open both petcocks for high speed.
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Precisely but that's due to the tap/petcock restriction not the fuel pipe diameter and the possibility of exhausting the main fuel supply at high speed. In any case opening both taps of a 1/4" line should then be more than adequate.

Even the owners handbooks for bikes with 5/16" fuel lines (T140 etc.) still recommend opening both taps for high speed running.
 
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Triton Thrasher said:
Are you saying not to open both for high speed?
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Actually, I said that I have no idea why Norton used 1/4" and others used 5/16". I meant nothing more than those words. Les replied as if I did. I then replied with a question. I've stated nothing except I don't know why Norton used 1/4" and others 5/16"
 
marshg246 said:
Actually, I said that I have no idea why Norton used 1/4" and others used 5/16". I meant nothing more than those words. Les replied as if I did.
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I don't believe I did at least not that I'm aware of.

marshg246 said:
I then replied with a question.
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There's no question I can see (as questions normally end with '?') only what appeared to be a statement that I basically agreed with.
 
Triton Thrasher said:
1/4” passages and hose can pass more fuel than a road Norton needs. That much I do know.
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Yes, although I think perhaps there has been something of a misunderstanding as it's the larger bore diameter of the 5/16" banjo fitting possibly allowing for greater fuel flow rather than the actual hose diameter, although with the 0.100" float valve restriction it seems doubtful that the larger bore of the 5/16" banjo would increase fuel flow.

The OP didn't state a reason for possibly wanting to fit 5/16" banjos whether it was a matter of if they would physically fit or something to be gained (as in increased fuel flow?) by doing so but only "Would it be possible...".
 
Apparently, the 0.1” needle valve is less restrictive than a 0.1”pipe of significant length would be.

Can’t get it written out in a neat way, but pipe length is a factor.

Volume flow rate = π X pressure difference X pipe radius 4 X liquid viscosity / 8 X viscosity X pipe length

Fuel banjos


sciencing.com

Flow Rate Vs. Pipe Size

According to Poiseuille's Law, the flow rate through a pipe at constant pressure and temperature varies with the fourth power of the pipe radius.
sciencing.com sciencing.com
 
Yes pipe length is a factor, in theory at least, IIRC this is Box’s formula ?

ie a 100 feet long 1/4“ pipe will flow less than a 100 feet long 1” pipe. And less than a 100 feet long pipe with a 1/4” restrictor in the end.

But how much practical meaning this has with short fuel lines I don’t know.
 
Generally speaking, Triumph uses 5/16" and with one tap open fuel must past through one banjo to get to the other. On the older Nortons, the "H" fuel line (06.1440) has no such restriction but may have at the "T"s - probably OK since the fuel lines are a reservoir of sorts. The later (06.5192) is like the Triumph lines. Considering that the 1/4" hose is 1/4" ID the ID of the 1/4" banjos is around 1/8". Given that .125 is not a lot more than .1; I can and do see filling problems with one tap open. Try it - run the bike dry (or drain the fuel lines), then turn on one tap and see hold long it takes for the other side to rise to the level of the fuel in the bowl.

Also, I've re-read several Triumph Owner's manuals and have found none that says to open both taps. Please state what manual says that if Triumph was implied.
 
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Fast Eddie said:
Yes pipe length is a factor, in theory at least, IIRC this is Box’s formula ?

ie a 100 feet long 1/4“ pipe will flow less than a 100 feet long 1” pipe. And less than a 100 feet long pipe with a 1/4” restrictor in the end.

But how much practical meaning this has with short fuel lines I don’t know.
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The practical meaning might show its ugly head if someone used 0.1” bore petrol hose from the tank to the carbs.
 
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