Originally Posted by earlwb
I had to replace the regulator diaphragm as it softened up and stretched out over time and stopped regulating, same thing for the pump diaphragm too, as it got all stretched out too. So I suspect the stock NGH rubber diaphragms are made from a rubber compound that doesn't do well with our American pump gasoline over time. If you use SEF or TRU-Fuel the rubber parts might last longer. Anyway it was easy to swap out some Walbro carb diaphragms to fix the problem from a Walbro carb repair kit This might be what makes people think that the fuel inlet valve is stuck or something, when it may really be the diaphragm has softened up and stretched out on them. I had swapped out a second pump/regulator unit that worked well previously and it did the same thing. That was what prompted me to replace the diaphragms then.
I have noticed a difference in the diaphragms manufactured in China vs Japan. I am
testing with 87 octane unleaded regular, and Yamalube 2R oil. I will keep an eye on
the rubber parts. In fact, I think I'll incorporate an hr meter into my data acquisition
Note: Does anybody know what California adds to our fuel blends that may harm rubber parts
faster than other states?