My classic trials Skoda Estelle is running Honda Fireblade bike carbs. At present I use a Facet cube pump and a Filter King to regulate the pressure to around 2psi. The vertical height between the tank take off and the fuel pump is around 12 inches I would think. Is that asking a bit too much for that kind of pump? It does work but I suspect a touch of starvation very occasionally at high revs in first going up hill. If so what should I go for or should I fit a bike fuel pump? Do bike pumps only work correctly with a gravity feed to them? Any opinions would be appreciated.

Not sure if this will help but here is my experience with this set up in a series land rover 3.5l with underseat tanks.

From memory the facet interrupter pumps are push type so need to be mounted low down, initially it was in the engine bay. maybe 1ft above the top, but moved to be a couple of inches above. I didn't notice any difference.

There were 3 variants differing by flow rate, I chose the middle on even though the smallest would have been sufficient. So check which one you have fitted and remove line to carbs, run or a minute to see how much fuel is delivered.

Reason why I relocated it was fuel starvation on accelerating, a word not normally associated with series land rovers, uphill. The cause turned out to be due to debris in the metal filter fitted at inlet to the pump. Easily fixed by removing it and tapping it on a wooden block. That would be the first thing I suggest you do, or look to fitting a larger filter instead because the facet one is quite small so will get blocked quicker, tiny when compared to the one fitted to a volvo 850, chapstick size vs energy drink can size.

[Edited on 3/3/19 by 02GF74]

I'd definitely recommend a bike pump. Mount it under the fuel tank.