Up until around year 2K the Walbro GSS307 and GSS340 shared all the same parts. The only difference was that the GSS340 had a heavier spring in its pressure relief valve. This allowed the GSS340 to operate at higher pressures before the valve would open to dump fuel back in the tank. People soon realized that by shimming / modifying the spring on the GSS307 the same performance could be had at a lesser price. The pressure relief valve is an important safety feature which prevents dangerous pressures being built up in the fuel system should the pump's outlet become restricted. Many vendors and customers started modifying the valve which must have been one of the contributing factors to Walbro's design changes to these pumps. Racetronix has seen performance tests conducted on GSS307 pumps many years ago where a shimmed GSS307 would outperform a GSS340. This data would be accurate in its day when both pumps shared the same armature but this no longer holds true. The sad part is that certain vendors use this dated information to sell customers on modified GSS307s just for the sake of putting a few extra dollars in their pockets. Current production GSS307 and GSS340 pumps no longer have an opening in the cap allowing access to the valve's spring. The current GSS307 has an armature design which is different from all of the GSS34x pumps in Walbro's lineup. This encapsulated armature is better suited to the lower pressure applications (under 60PSI) for which the GSS307 was originally intended. When compared to a GSS340 the GSS307 will draw more current to produce the same pressure. Many would ask why offer the GSS307 if the GSS340 can provide better performance all around? Perhaps the original idea was the price point? At one time normal retail on a Walbro GSS307 pump was around $200US. Today it is not uncommon to see the same product being sold for around $100.00. The cost difference between the two pumps is only a few dollars. Racetronix has therefore decided to discontinue offering the GSS307. Where applicable current product will be bundled with GSS340 pumps only. We believe this is in the best interest of our customers. 

Please see our  info on Walbro's release of the F20000169 pump which was designed to replace the GSS340M which is a GSS340 with a machined inlet.