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.

 

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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, 2024 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.

[kram]

Have not yet reassembled the cs340 although the carb appears to work, that can wait.

 

Started on the KM111R, needed a lot of cleaning! New purge bulb and will need a new air filter. Starts and idles well enough.

Only thing I notice, if I release the purge bulb quickly, its sucking in air bubbles from somewhere, bubbles up the hole in centre. If I release slow, over 10 seconds or so, no air gets in. Not enough to cause problems but any idea where from?

 

 

 

 

 

[kram]

Km111R is now fixed. Adjusted the valves which were loose. One issue left is the choke butterfly shaft was not returning freely and needed a clean. I got the circlip off ok, but the return spring has sprong somewhere in the distance but it was likely broken anyway. Part I need is out of stock everywhere, 4180 122 3008. Cleaned up the corrosion and oiled the shaft so it moves free and reassembled without it.. not really needed just for the user to turn it back after starting.

 

It starts much better and easier with the valves correctly adjusted!

 

Edited January 7 by kram