Must be more pulse pressure in the Shindaiwa...Try weakening the small spring under the inlet needle so it takes almost no pressure to open it...They work from atmospheric pressure on the diaphragm, and a really weak spring sometimes works better..It normally takes anyhwhere from 10 to 15 or more pounds to unseat the needle, but if you can make it weaker it might work better.....You need only enough pressure to keep it from leaking when the engine is not running..We set the pressure at about 5 lbs on our methanol fuel race engines....Weaker springs are available from Walbro, or you can carefully clip the spring a little at a time...