Carb purge bulb air leak woes

[Dan Maynard]

It's a while but I used to do some mechanical design.

 

Measuring the groove rather than the Oring is wise, there's a standard to fit bores and another for shafts. You should need a 5mm diameter, 1mm thick ring. This will compress slightly between the 3.2 and 5 (groove depth 0.9) but not fill the groove sideways. 

[peatff]

ID is internal diameter CS cross section is the thickness of the rubber so OD outside diameter is ID plus two times CS.

[Dan Maynard]

https://simplybearings.co.uk/shop/p80406/1mm-Section-3mm-Bore-NITRILE-70-Shore-Rubber-O-Rings/product_info.html

 

These would be a standard, you might want to investigate materials for ethanol fuel, or might find a softer shore in something like silicone rubber. Bit of trial and error.

[kram]

Nitrile is no good with modern fuels. I believe it is supposed to be Viton for fuel/ethanol resistance?
 The original was black and I'm assuming nitrile as it didnt last long.

 

Anyway I have gone with the fast option, 9am Sunday delivery.. pack of 25 for a fiver.

 

sourcing map Fluorine Rubber O Rings, 5mm OD, 3mm Inner Diameter, 1mm Width, Seal Gasket Black 25Pcs : Amazon.co.uk: DIY & Tools

WWW.AMAZON.CO.UK

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Free delivery and returns on all eligible orders. Shop sourcing map Fluorine Rubber O Rings, 5mm OD, 3mm Inner Diameter, 1mm Width, Seal...

 

They fit well, purge bulb instantly works and squirts the remaining water that was left in the carb, put it back together and ready to reassemble the saw.

 

I'll attempt to check over the KM111R later.

 

Edited December 8 by kram

[Dan Maynard]

Yes viton is what we used to put in pharmaceutical jobs as better chemical resistance, or silicone rubber. Also in that case to do with alcohol resistance and subsequent not leaching chemicals back out.