Have you changed the dizzy? if so try turning it to different position and keep trying.
I have just put my metro 1275 eninge back in and had same problems, I had the wrong firing order.
The sparks go 1-4 starting at the rad end, the dizzy if you have vacuum advance with the mushroom shape at the top going round clockwise should be 1,2,4,3.
Hope this helps.
We say 1-3-4-2 asd the rotor arm spins anti clockwise.
You can get timing close by removing the plug from cylinder one, and turning the engine until you reach TDC with both valves shut. The idea is to find TDC at the end of the compression stroke / start of the expansion stroke.
Now you can see where the rotor arm is pointed, and you want to rotate the dizzy until the contact for cylinder one is in this same location.
To get timing better adjusted a timing light is much better.