hi
My 1971 (1600cc) kombi is having a strange engine out of tune or miss firing problem.
The trouble starts when the petrol tank gets down to 1/4 full. The engine will start to splutter. As the petrol level lowers the bad engine running gets worse. If I fill the tank anywhere over half the problem miss goes away after about 500 meters of driving.

Could I have some bad gas floating in my tank? Does the petrol like to be pressurised and when there is not enough volume there is no pressure?

Thanks in advance - Carl.

-could be all the crap in your tank is concentrated in the less fuel and blocking the hole to the engine
-could be water in the fuel tank

I'd guess that the outlet is partly blocked & only works when you have a full tank because you have a good "head" of pressure to push fuel out. You can fix it temporarily by disconnecting the fuel line going into the pump & blowing back towards the tank with compressed air. But you may need a tank clean-out.

Could also be a fuel filter almost blocked (if you have one) or a fuel pump on the way out.
Try checking the float level both when it's missing and when it's running fine. Will confirm if it's definitely lack of fuel causing the fault.
:thumb

This one got me too... The answer... Vent the cap!
I found that my fuel pump was sucking the tank into vacuum and it got harder and harder to run as the tank got lower ..just think everytime you put some more fuel in it you are also opening the cap! and venting the tank . Does it whoosh when you open the cap?
I hope this will help
Silver

Good one silver, never thought of that!
If that's the problem, fix the stock breather system rather than drilling the cap, it will get filtered air that way and won't leak from the cap when it's full.

thanks for everyone's input. Sometimes the simple things work best. undoing the petrol cap seems to overcome the problem. Oh yes I put the cap back on again.