Fuel line routing

tcyrenne

Vintage rider, newbie home builder
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Hello everyone,

I am dry fitting my fuel lines today, I'm wondering if anyone sees any issues with my mock up. I'm looking for issues such as possible flow restrictions, heat concerns etc.

What my photos are trying to show is:
I have a 3 way splitter which joins the 2 petcocks and the 1 flows down to the fuel filter. The fuel lines loop down then up from the petcock to the 3 way. The 3 way seems to be either at the same level as the petcock or a bit lower.

I will be installing a stop valve, my best guess for placement is placing it in the line between the 3 way valve and fuel filter. I have seen a 3 way with a shut off valve, I had forgot to bookmark where I found it so I'm having a hard time finding it again tho.

Please let me know if I might run into fuel flow issues, of if the lines are too close to the carbs/engine

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Yes, I think all your lines are a bit too long, forcing fuel to try and run up hill. I would shorten all 3, especially the outer ones.
 
The yellow Tygon is called F-4040-A and has a 6.4mm ID - UK Cost approx. £10 per meter.

Another possibility is to use smooth Nitrile rubber fuel tubing ID 5mm OD 8mm - UK Cost approx. £4 per meter. It is not as bulky and more flexible than the reinforced nitrile rubber you have fitted.

Whenever you have a petrol tube looping up there is the possibility of a vapor lock occurring. It is quite warm behind those cylinders and vapor locking will happen if your fuel lines get too close to the cylinders/head and especially if they touch.

You indicated you would fit a stop valve. If you do not then you run the risk, if the carburetor float valve sticks open at some point, of flooding the crankcase via the piston ring path. Your fuel outlets on the tank look far enough back that you could use just one if it makes life easier.

Enjoy the work and keep an eye out for a nice fuel stop valve.
 
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The tin top bs34 carbs are factory run by a single petcock to the carbs crossover T, no worries about fuel starvation.
Like Paul says above it's best to have a shutoff on that fuel line ........and use it.
 
Lawnmower repair places might carry the Tygon tubing, but they are sure to have the smooth black nitrile rubber.
 
On the fuel starvation question, I run 2 petcocks to a "T" and down to a fuel filter like you have to the BS 34s. I turn on the Left side petcock only. No problems. Add the breather line now too so you can factor in the amunt of space of ALL those hoses compeating for the same space. It gets really crowded fast. Perhaps runnung some 90* fittingw will help with your routing.
 
I’ve purchased the Princess Auto stuff but my regular ho to place is my local small engine shop. They carry at least 4 diameters of Tygon. Cost per foot may be a bit higher than other sources but it’s convenient and also supports small business.
 
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