5hp briggs wont start!!

[LADDERMAN643]

5 hp B&S horizontal shaft, siphon carb. ,first the troybilt tiller was ran on varnished fuel-exhaust valve was stuck . no compression do to stuck open valve. Fuel tank had loose rust in it.
rebuilt carb and and cleaned fuel tank out . replaced head gasket after getting stuck valve loose.cleaned head etc. replaced air filter also,
started tiller, tilled a while with it ok- next day started again and it ran 15 second and died-wont start. broke pull rope fix it . tried choking no good. back fires thru carb if choked .have spark and fuel and compression. what happen?

[Restrorob]

back fires thru carb if choked


The above is a sign of a intake valve not seating fully.....

[LADDERMAN643]

well the valves were ok - I found a loose lift tube on siphon carb -it was lose in fuel tank--by the way hows does this plastic lift tube install?-do you heat it up to install?
too tight to slip on
model 130297 5hp briggs horizontal shaft-gas engine.