Toppingcat

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

hey sorry i completely forgot about this forum i actually got a polini carb about a week ago and fitted it as the phva was leaking anyway, just wanted to thankyou for your reply i did cut those bits off the manifold and im glad it was the right thing to do thankyou very much for the reply and sorry for the late reply

lowered the jet to 72 and it ran like crap, so put the 88 back in and it worked better so we went up to a 95 and its the same as an 88, dont think the problem is jet related we are thinking maybe cdi related?

Ok thanks i will try lowering the jet, im fairly confident this isnt the issue however as i think around 70 is the standard, any other advice will also be greatly appreciated

im not entirely sure what the standard is i think it is 68 but with the aftermarket jet i thought up jetting was the right thing to do, i do have a rev counter but it dosent work properly it sometimes works sometimes dosent im not sure why

Hi i have just bought a 50cc derbi senda sm xtreme 2008 model. when i bought it there were a few problems such as exhaust leaking, air filter being in pieces and jets were too big (82). i put on a "big one" aftermarket exhaust and downjetted to 72.The guy i bought it from said that he had recently had a top end rebuild on the bike. when you get up to about 35mph it bogs out, it also sometimes has trouble starting up.any advice on how to fix this will be much appreciated