derbi senda problems

Hi i have a derbi senda 50. I have had it since august of last year hoping to have it fixed by September and it still has problems.A few weeks ago it was riding ok, the bike should be capable of aleast 55mph but would only get up to around 35 on flat ground and 40 downhill, i noticed milky oil so did a water pump rebuild.The bike is now back together, i went for a short ride a few days ago to test it out, it was riding fine until i got to a downhill sectioon, i rode the bike slightly aggressively and it died going about 40mph in 3rd or 4th gear.i had to pull over and tried kickstarting it felt like i had a sudden loss of compression and it wouldnt start even after about 30 kicks varying between having choke on and off.I pushed it home and left it for a few days before trying again, i noticed i was out of fuel so went to get moe but put in way too much 2 stroke oil which i thought might of caused me not being able to start it (later on) so i drained all the petrol and put in the correct ratio.I tried it out again and got about half a mile before it stalled in first, after stalling it wouldnt start at all with choke on or off, so i tried bumping it and it wasnt starting and again it felt as though i had lost compression so i walked it home and wrote this, any advice would be very much appreciated as im completely lost.

modifications:

unrestricted CDI

"Big one" exhaust

19mm polini carb

carbon fibre reeds

main jet:90

pilot jet: 40