I have had this happen several times for at least two different reasons:
(1)The air valve (a pin-hole) in the gas cap is plugged thus creating a vacuum in the gas tank causing the fuel to not flow efficiently. If the cap is plugged, Just clean out the valve hole (actually, I used a small drill bit to make the hole larger in mine).
(2) The air filter can be very dirty/plugged .... thus carbuerator not getting the air it needs to handle the extra load of the blade being on. Clean or buy a new filter and wash/rinse out filter sponge with soap and hot water .... this is the sponge that wraps around the air filter. Dry it then put a bit of oil on it and then squeeze the excess oil out before replacing back around the filter.
(3) A final possibility might be that your carburator may be real dirty .... and needs to be disassembled and cleaned with solvent, etc. ... OR it may possibly just need to be adjusted.
Hope this helps ......Good luck!
JPMM, June 2010
