Vaccuum being created in the tank, possibly? Removing the cap allows air to enter, solving the isuue?

Rob

Setting the scene:
You have a 'chicken feed' fuel system. The pipe from the removable tank descends into a sump that has the tube horizontal to the burners. The level in the sump is kept roughly constant so the burners have a steady supply, not too much or too little.
The tank must be sealed, NO little air hole or it will drain itself all over your feet.
From the start with a dry sump the dip pipe comes from the bottom of the tank so a gulp of air goes up the tube and a bit of meths comes down, just like when you turn any bottle of liquid upside down and teh sump fills.
However when the sump fills up the end of the tube is below the liquid level (it must extend far enough for this or again – wet feet) so no air can get up the tube to let more meths out. As the meths burns and the level drops it is possible for another gulp of air to get up the tube and meths comes down until the tube is covered again.
It is a simple but effective system invented to provide chicken pens with water from a bigger tank because chickens like a shallow trough and won't drink from a bucket or stream.

Issues:
Surface tension can stop the flow. To help the transition from covered to allowing air up it is common to cut the end of the tube off at an angle, 45 or 60 degrees.
it is also possible to use two tubes, both ending under the level in the sump but one from the bottom and one to the top of the tank.
There is often a valve to stop it dribbling during loading.
it helps to start with some air in the tank not filling it right up.

Wicks – assuming the problem is a dry sump not just flow up the wick. The wick needs to be quite loose almost falling out not stuffed in as hard as possible as more wick does not equal more flame.

Join the gauge 1 forum on Groups.io as there was a discussion last year on wicks and Aster steaming.

If the meths flows when the filler cap is unscrewed, the meths tube must be adequate.

This suggests the air pipe from the sump into the meths tank is either too low in the sump or blocked.

I would check the “air tube” is patent.Also check if there is some way for air to get into the sump – I had one loco that wouldn’t steam and found the top of the sump was built hard against the bottom of the meths tank – there was no way air could get into the sump to be drawn up the air tube and relieve the vacuum in the meths tank.

If that’s ok then with the loco on a flat surface measure half way up the burner tube and mark that dimension on the meths sump. Then remove the sump and see if the breather tube (aka air tube) ends at that level. If it’s below then it needs trimming or the meths tank needs raising with a spacer.

Ralph

As a side story to vented fuel filler caps. Many years ago the family car began to stall at infrequent intervals, often inconvenient too. After a few minutes it would start again and run for a while more before repeating this behaviour.

We discovered by chance on checking the fuel level that the tank itself was under partial vacuum and yes, there was a blocked vent hole which was the culprit.

There was a sting in the tail too, the fuel tank bottom had bellied upwards and it then only held about 3/4 of capacity; worse still, the take off point became exposed above the fuel well before the indicator suggested otherwise and in the end it had to be replaced.

Brian