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Fuel Tank Venting

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Old 15-09-19, 12:19 PM
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Default Fuel Tank Venting

I get fumes into the car for quite a few miles after filling up.

I tried to cure the problem by fitting a one way valve in the vent but, because the vent comes off the top and the filler goes in at the bottom, the tank would only fill up to the quarter full level.

Has anyone had this problem and found a cure? It is hard to curb my enthusiastic driving for 40 - 60 miles after filling up!
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Old 16-09-19, 07:36 AM
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peterg,
It might help if you advise what type of Bristol you are referring to .
The various 6 cylinder models have quite different fuel tanks
Geoff
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Old 16-09-19, 12:02 PM
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It is a 403, Geoff.
The new ss tank is a close copy of the original. As said, the entrance is at the bottom of the tank and there is considerable scope for petrol to shoot up the 3/8" breather pipe into the filler cap box with a full tank.
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Old 16-09-19, 09:03 PM
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peterg,
a few things to consider

Is your new tank baffled ? If not it might push fuel up the breather on corners.

Are the fuel sender unit and fuel reserve unit sealed correctly to the tank?

Try not filling the tank so full and see if you have the same issue .

If fuel is pushed up the breather it should enter the filler cap well and drain to the road. There should not be fuel vapour entering the cockpit unless the well is rusted or not sealed correctly. Is the drain pipe in good condition?

When you fill the tank do you get fuel coming up the breather?

Geoff
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Old 17-09-19, 09:02 PM
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Quote:
Originally Posted by Geoff Dowdle View Post
peterg,
a few things to consider

Is your new tank baffled ? If not it might push fuel up the breather on corners.

Yes it is, but there is a limit to the baffling effect with a full tank

Are the fuel sender unit and fuel reserve unit sealed correctly to the tank?

Try not filling the tank so full and see if you have the same issue .

I tend to fill it right up to get an accurate fuel consumption figure

If fuel is pushed up the breather it should enter the filler cap well and drain to the road. There should not be fuel vapour entering the cockpit unless the well is rusted or not sealed correctly. Is the drain pipe in good condition?

Yes but the underside by the filler tube is not as complete as I would like, so vapour can get into the boot and circulate into the cockpit.

When you fill the tank do you get fuel coming up the breather?

I get a squirt as I push the cap home. I'm wondering if I should install a cross link between the breather and filler. That would allow the one way valve to be used, but would raise the issue of pressure build up or would it bleed off into the carbs?

Geoff
Some thoughts on the matter
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Old 18-09-19, 12:18 AM
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peterg
I would try to get your car back to original design if possible .

Replace any rubber tubes with modern rubber/neoprene that is not effected by fuel or oil .

Fix any holes in the fuel cap well and make sure any fuel that comes into the well drains on to the road.

Remove the one way valve it should not be necessary if every thing else is in order.

Dont fill the tank as full as you have been doing.

Hopefully one or a combination of these will fix the problem.

Geoff
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