RE: cox 049 will not start
Your engine will run on 20%. The oil content is more important and should be in the range of 18% to 20% with the majority being castor.
It sounds like your engine is running on prime only my inclination is that your venturi/NV is likely clogged with congealed castor and is blocking fuel flow. When you replaced the fuel pickup tube, did you use the same tube or new fuel tubing. Generally, we usually toss the old tube because is has hardened and will allow the engine to suck air where it attached to the fuel nipple on the backplate.
Remove the needle and flush the NV seat well with fuel. You can also add fuel to the air inlet screen on the backplate. To check the reed for seating, remove the tank, wipe the reed housing clean and place your mouth over the reed housing. By alternately sucking and blowing air, you can determine if the reed is seating. You should be able to easily suck air past the reed, but when blowing lightly, the reed should seat and not allow air to pass. If you have a syringe or fuel bulb, pumping fuel under pressure into the fuel nipple will help clear any blockage around the NV seat.