1987 J50TLCUD newbie

[gone fishing]

I have just inherited my step dads shed-he was a boaty ,made on johnsons
wall to wall,must be at least 40 or 50 years collecting and repairing outboards *** ya should see this shed outboard stuff every where ya look.
pitty that I did not get to no him in his shed,he was my step dad for 24 years
and looking in his shed I think I hardley new the man...
I have picked out a 50hp seahorse Johnson VRO job looks to be in pritty good shape for it age I would like to put it on to a boat from out the back of his shed.
I got it on the test stand it starts ok runs ok but when you reve it it back fires and almost stops ,motor has been sitting for some time not sure where to start. never worked on an outboard before but have been car made most of my life so have some spanner skills.
it seems to be getting spark ok to both pots and fuel is definetly getting in some how . have flushed both carbs out and they both look ok I am thinking it maybe a spark prob underload any ideas?
thanks Brett

[boats.net]

Check timing and the timing advance. Make sure all linkages are moving. With a timing light you can see if you loose spark at high rpm. When cleaning carbs make sure every air/fuel passage is clear from debri.

[gone fishing]

thanks for the help
turns out that the jam nut that affects the throttle cam had came loose
and requierd screwing up so that the cam came incontact with the carbei roller to help sinkcranise the advance with the carbie,s .
(linkage synchronization problem )
although looking at the timeing under load told me that it was still fireing helped ''that lead me to finding the problem.
by manuely advancing the timeing and the throtle at the same time
the motor reveved up ok no back fireing.....

next problem after a short while the fuel filter runs out of petrol and motor stops ,if you keep priming the fuel bulb the motor keeps running
i suspect the fuel pump may be not working correctly
any ideas on this one .....not sure where the fuel pump is on this model
or how to see if it is working properly
i have checked fuel filter and clenend it out , and all fuel leads for leakes right back to the fuel tank all looks ok
how do i test fuel pump and where the heck is it.......
still whaiting for workshop maual to show up in the mail till then not sure wot gives ....