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@750 R1: First off, please don't give me any credit for the welding on the tank - if I could do that I'd quit my day job
I know what you mean and it should stop the flow a bit. I'd still go with a valve like Wookie posted or the one on my tank. My valve is pretty simple. There's a ball in the bottom section that floats up and seals against the top part of the valve whenever the fuel level rises. It should work pretty well and would be pretty easy to make. Worst case I can just drill out the bung and fit one of the valves Wookie linked. I'm not sure how my valve would go if the bottom section was inside your box - it would probably need to extend down into the tank.


@scirocco & Wookie: I need a bit of help on this one I thought an inline check valve would just stop fuel flowing back through the line (not really a problem here). How would it help to vent the tank? Or have I misunderstood "inline"?

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@750 R1: First off, please don't give me any credit for the welding on the tank - if I could do that I'd quit my day job
I know what you mean and it should stop the flow a bit. I'd still go with a valve like Wookie posted or the one on my tank. My valve is pretty simple. There's a ball in the bottom section that floats up and seals against the top part of the valve whenever the fuel level rises. It should work pretty well and would be pretty easy to make. Worst case I can just drill out the bung and fit one of the valves Wookie linked. I'm not sure how my valve would go if the bottom section was inside your box - it would probably need to extend down into the tank.


@scirocco & Wookie: I need a bit of help on this one I thought an inline check valve would just stop fuel flowing back through the line (not really a problem here). How would it help to vent the tank? Or have I misunderstood "inline"?

The inline valves still have a ball set up and work fine if bulkhead mounted in an upright position (in a car) but if they are not upright they can allow fuel to pass without pushing the ball to shut off the outlet (which is what happened to me  )

Thanks, still a bit confused about the term "inline". Where exactly are they mounted?

Edit: I'm assuming we're talking about this sort of thing mounted in the fuel line at the bottom of the tank.
www.newton-equipment.com/in-line-valve-range.html
Still a bit confused about how it would allow air to pass through to the top of the tank... Or am I just way off track?

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Thanks, still a bit confused about the term "inline". Where exactly are they mounted?

Would be something like the below where you have a "pipe" outlet welded into the tank, there is then a hose from the tank to the valve and another hose from the valve to atmosphere

 

Thanks, now I've got it. I assume the pipe fitting goes far enough into the tank to be above the fuel line - that was the missing piece of the puzzle

Back home and getting back into things. Got the Zephyr running so back to this project tomorrow. Picked up the bolts for the bottom end so I'll put that together and get it in the frame. Can hopefully get the head and cylinders painted on the weekend otherwise I'll just bolt them on as is so I can get the exhaust bracket done. 
I unpacked the tank today and got the seat off the shelf just to see how it looks. The tail is a lttle bit steeper than I would have liked but I think I can learn to live with it

 

 

 

Coming together pal, looks good

Thanks. Hopefully I can get the bottom end in the frame and the wheels on tomorrow, then it'll start to take shape. Your seat pan is looking good, any more progress?

Remember, one of the most common motorcycle accidents is when our right of way is blocked, thus, we T-bone the offender.  And when that happens, we are flung forward, while straddling the gas tank.  Need I say more?  In other words, keep any tank protrusions LOW, so they don't snag any critical parts in the event of an emergency. 

Oh, and those welds look to have been done with a silicon bronze rod.  My welder/machinist buddy loves that stuff since it's low heat.

True, best not to think about that too much  The valve will end up being a bit lower than the top triples and quite close to them, the hose going to the steering stem should help any critical parts slide over the front end

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Thanks. Hopefully I can get the bottom end in the frame and the wheels on tomorrow, then it'll start to take shape. Your seat pan is looking good, any more progress?

Thanks, pan is about done now. It's been a mission because of the issues with getting anything to stick to polypropylene which the pan is made off. The underside is a little ugly where it's been "pie cut" lengthways but I really liked the fact that the curvature perfectly matched the shape of the side panels so I have persevered with it. 

I got the bottom end pretty much together (still a bit to do, but the cases are back together so I could get it in the frame). Will put the cylinders and head on loosely tomorrow so I can see where the exhuast bracket needs to be. Then I'll get to work on the cockpit.
All the engine mounts lined up (with a bit of encouragement) except the right rear upper bracket. It's quite a bit off so I'm wondering if all the 900/1000 brackets are the same or whether I've ended up with the wrong bracket as I don't think the frame is that bad. The bracket on my other build has a hole in the middle and this one doesn't.