I am not quite sure what the mechanic did. He checked the valves and apparently did start it using a fuel line connected to a can of fuel. I replaced the filters (twice) all fuel lines, strainer, primer pump, ball joint in on the fire wall, checked the adjustment of the accelerator linkage, (it appeared to be OK). I really don't think they checked that pump timing. This happened suddenly, I didn't mention that. I also replaced the shut off valve. The problem started about a week after that.