Oxidizer to Liquid Fuel Usage Ratio

[Arcane]

Tried to make a heavy carrier for large scale equipment and parts to take into orbit and other planets etc. Even for a behemoth, I can get into orbit and beyond steadily just fine, however the oxidizer runs out far too quickly and the engines cut out before the fuel is depleted.

What I've tried already:

-Use only or majority of the ship's engines as CR7 Rapiers: Far too inefficient to get into orbit in the first place.

-Decrease fuel LF amount to evenly match Oxidiser amount or lower: Same problem. Continues to use more Oxidizer than Liquid Fuel.

-Send a fuelling ship from a refuelling station: Can't even get into a stable orbit before Oxidizer runs out. Will just crash back down to Kerbin.

The only problem with the ship is the Oxidiser usage, otherwise it's decent enough for what I need. The ship mainly uses the MK3 fuselages which is where this problem seems to occur the most. happens with the MK3 rocket fuselages, yet there's far more oxidizer than Liquid fuel. Tried looking this up but couldn't find any answer.

[Ogre420]

Better check and see if you are not using a PLANES fuel tank (LF but no OX).

You need fuel for planes and LF/OX for rockets.
The rapier needs a jet fuel tank for the PLANE mode & rocket tanks for ROCKET mode.

Using all rocket fuel tanks (LF/OX) this leads to excess OX in the tanks as the plane mode eats some of the fuel.

If you are getting excess LF then your packing too much jet fuel for the launch. (If it's a space plane remember to have some for the re-entry flight)

NOTE : The normal ROCKET fuel tank packs about twice the amount of OX then LF (I forget the exact LF to OX ratio)

[Arcane]

I know they're mainly used for planes, except it said 'Mk3 "Rocket" Fuselages.' (there are two types, one for planes and apparently one for rockets. The one for planes doesn't have any oxidizer) however, I'm just trying to a get a Mk3 type payload into orbit as it's the only one big enough to carry what I need and using fairings would cause a weight imbalance. It would just look a bit odd with a Mk3 payload on a round rocket fuel tank though I suppose that's more optimal.