carb kit pump diaphragm, differing materials

[flatsfisher]

did a carb kit for my 028 Super. used a Walbro branded kit. in the kit there are 2 different pump diaphragms, a black rubberish one and a plastic blue one (also one that looks like kevlar but doesn't have the flaps so let's forget that one). I used the black one because that was what was in the carb when I opened it. of course, this carb has likely been kitted multiple times in the last 38 so who knows if it was right. what is the difference between the black one and the blue one? is one for ethanol and one for non eth? thanks.

in the photo, the black one is the one I took out in case you notice its used.

 

[hotshot]

That’s the right black diaphragm for your 028S. The blue came out later & supposed to resist ethanol better & have a longer life if you have no choice but to run ethanol laced gas.

Strange to see that tan teflon backer gasket in there, Walbro should put a teflon type pump diaphragm in their kits too.

This pic was posted a while back from an aviation site for RC planes…the material is described right, but I think the black nitrile has the highest pump rate or volume.

https://www.arboristsite.com/threads/carb-diaphragm-materials.359235/unread

 

[flatsfisher]

great info, thanks! all I use is non eth except for my vehicle.