I just finished a DOHC swap in my 90 240 and I was also having starting problems. It turned out that my timing was way retarded. I even timed my motor like the FSM by lining up the dots on the distributor and it was still off.
Put your motor at TDC on the compression stroke and pull your distributor cap off. The rotor should line up with the #1 spark plug. If not, try following these step;
- Take out the #1 sparkplug and stick your finger in the valve cover hole creating an air tight seal in the spark plug well.
- Turn the crank clockwise with a ratchet and a 27mm socket
- You'll feel air coming out of the hole and as soon as all of the air is expelled, the timing marks on the crank will appear.
- Set the timing pin to the 2nd mark from the left - TDC on the compression stroke.
- Now pull off you're distributor and take off the cap.
- Line up the dots on the disributor and try putting it back in.
- If the rotor is on the #1 plug wire, you'll be ok.
- If the rotor is off towards the #2 wire which it was in my case, pull the distributor out and turn it counter clockwise one tooth.
- Your rotor should now be pointing to the #1 spark plug wire.
- Put your cap back on and it should fire right up.
- Let the motor warm up, disconnect the TPS and fine tune timing with a timing gun.