Sounds more like a tuning problem. Does it instantly have a problem when you open the secondaries, or did it develop over a period of time? (what I mean about that is does it work fine till it runs all the fuel out of the carb bowls?)
Have you went back to the basics and "proved" what is right with the timing, plugs, ect? What color are your plugs right after you think it is running out of fuel?
After you "know" what else is right, then work on tweaking whatever is left. Could be a combo of several problems.
The more info you can provide, the better we can provide acurate fixes. Let us know what your intial timeing is, then with it fully advanced and at what rpm its all in. Do you have the accelerator pump adjusted so it squirts instantly as soon as you open the throttle?