Walbro WJ carb without a check valve?

[bmp01]

I think this will be of little interest to most but I’m wondering if there is anyone with interest and knowledge of old Walbro WJ carburettor’s….

I have this Partner 7000 pro saw, bit tatty but it’s all there and has frightening compression. It will pop with some fuel thrown down the intake so I headed to the carb to see what’s what.

Well all looks surprisingly good, no fuel rot, no dirt in filter, diaphragm and pump all good blar, blar…. But the main jet check valve, didn’t work (surprisingly given general condition). And here’s where I ran into ‘issues’ - it seems like it was never supposed to work…. there is nothing in there that looks like it could act as a check valve. See picture of items that came out.

 

 

[bmp01]

I happened across some WJ parts list that suggest the WJ carb had the option of not having a check valve.

 

[bmp01]

Items 56 filter, 1 retaining ring, 23 plug are the same as mine ( I shouldn’t have removed the jet (LH part in my pic above) apparently 🙄

Item 20 check valve is an alternative fit part (that’s why it’s not highlighted).

 

Weird, a carb with the option of no check valve ??? 🤔🤔

 

[openspaceman]

3 hours ago, bmp01 said:

Items 56 filter, 1 retaining ring, 23 plug are the same as mine ( I shouldn’t have removed the jet (LH part in my pic above) apparently 🙄

Item 20 check valve is an alternative fit part (that’s why it’s not highlighted).

 

Weird, a carb with the option of no check valve ??? 🤔🤔

 

I haven't got a proper hang of these check valves but the main jet venturi is only under higher pressure  than the diaphragm chamber when the throttle is shut and the downstream idle outlet is  subject to full manifold depression.

 

I still wonder  if blocking this would overcome the problem at the expense of idling??

 

I still have a strimmer with  the problem of air getting into the chamber via a leaky check valve to fix, along with a heap of other engines that need attention. Will probably have to wait till spring.